Molecular phylogenetics and classification of Euphorbia subgenus Chamaesyce (Euphorbiaceae)

Abstract

Euphorbia subg. Chamaesyce contains around 600 species and includes the largest New World radiation within the Old World-centered genus Euphorbia. It is one of the few plant lineages to include members with C3, C4 and CAM photosynthesis, showing multiple adaptations to warm and dry habitats. The subgenus includes North American-centered groups that were previously treated at various taxonomic ranks under the names of “Agaloma ”, “Poinsettia ”, and “Chamaesyce ”. Here we provide a well-resolved phylogeny of Euphorbia subg. Chamaesyce using nuclear ribosomal ITS and chloroplast ndhF sequences, with substantially increased taxon sampling compared to previous studies. Based on the phylogeny, we discuss the Old World origin of the subgenus, the evolution of cyathial morphology and growth forms, and then provide a formal sectional classification, with descriptions and species lists for each section or subsection we recognize

Full text

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IntroductIon
Euphorbia L. (Euphorbiaceae) has about 2000 species
worldwide and is well known for the remarkable diversity of
succulent and non-succulent plants that are avidly grown by
horticultural enthusiasts. The entire genus is characterized
by the presence of a cyathium, a unique inflorescence type
(Prenner & Rudall, 2007; Prenner & al., 2011). The genus ap-
pears to have originated in the Old World (Steinmann & Porter,
2002), with multiple New World groups embedded in it. The
largest New World lineage consists of more than 500 species
that are characterized by the presence of petaloid appendages
subtending the cyathial glands, although this feature has been
subsequently lost a number of times. This petaloid appendage-
bearing, New World group is deeply nested within Old World
groups, and together they constitute Euphorbia subg. Chamae-
syce Raf. (Steinmann & Porter, 2002; Bruyns & al., 2006; Horn
& al., 2012a). Subgenus Chamaesyce is best known for its leafy,
non-succulent, ornamental species, such as the Christmas Poin-
settia (E. pulcherrima Willd. ex Klotzsch), one of the most
profitable potted plants in the world. Other widely cultivated
members are “Snow-on-the-Mountain” (E. marginata Pursh.)
and “Diamond Frost” (a cultivar of E. graminea Jacq.). It also
includes a large number of cosmopolitan weedy species such
as the spotted spurge (E. maculata L., Fig. 1E).
Among the four subgenera of Euphorbia, Euphorbia subg.
Chamaesyce is the second-most species-rich, encompassing
around 600 species worldwide. It is highly diverse in growth
forms, including annual and perennial herbs, shrubs, trees,
and pencil-stem succulents (Fig. 1A–E). Notably, it is the only
plant lineage at or below the level of genus that has all known
photosynthetic types: C

, C

and CAM (Webster & al., 1975),
plus a C

system that represents an early stage of C

to C

transition (Sage & al., 2011). C

photosynthesis evolved once
within Euphorbia subg. Chamaesyce sect. Anisophyllum, and
this C

group subsequently diversified into approximately 350
species worldwide (Yang & Berry, 2011); C

photosynthesis
also evolved once, again in sect. Anisophyllum, and is present
in two species restricted to southwestern United States and
northern Mexico (Sage & al., 2011). CAM photosynthesis, in
contrast, evolved multiple times in subg. Chamaesyce in both
the Old World and the New World (Horn & al., 2012b).
Due to widespread convergence in growth forms and
cyathial characters, subgeneric classification within Euphor-
bia has been notoriously contentious. The current scheme of
four subgenera is based on molecular evidence. All molecular
phylogenetic studies to date support all cyathium-bearing spe-
cies as forming a monophyletic Euphorbia s.l. (Steinmann &
Porter, 2002; Bruyns & al., 2006, 2011; Park & Jansen, 2007;
Zimmer mann & al., 2010; Horn & al., 2012a). These studies
Molecular phylogenetics and classification of Euphorbia subgenus
Chamaesyce (Euphorbiaceae)
Ya Ya n g,1 Ricarda Riina,2 Jeffery J. Morawetz,3 Thomas Haevermans,4 Xavier Aubriot4 & Paul E. Berry1,5
1 Department of Ecology and Evolutionary Biology, Universit y of Michigan, Ann Arbor, 830 North University Avenue, Ann Arbor,
Michigan 48109-1048, U.S.A.
2 Real Jardín Botánico, CSIC, Plaza de Murillo 2, Madrid 28014, Spain
3 Rancho Santa Ana Botanic Garden, Claremont, California 91711, U.S.A.
4 Muséum National d’Histoire Naturelle, Département Systématique et Evolution, UMR 7205 CNRS/MNHN Origine, Structure
et Evolution de la Biodiversité, CP 39, 57 rue Cuvier, 75231 Paris cedex 05, France
5 University of Michigan Herbarium, Department of Ecology and Evolutionary Biology, 3600 Varsity Drive, Ann Arbor,
Michigan 48108, U.S.A.
Author for correspondence: Paul E. Berry, peberry@umich.edu
Abstract
Euphorbia subg. Chamaesyce contains around 600 species and includes the largest New World radiation within the
Old World-centered genus Euphorbia. It is one of the few plant lineages to include members with C

, C

and CAM photosyn-
thesis, showing multiple adaptations to warm and dry habitats. The subgenus includes North American-centered groups that
were previously treated at various taxonomic ranks under the names of “Agaloma ”, “Poinsettia ”, and “Chamaesyce ”. Here
we provide a well-resolved phylogeny of Euphorbia subg. Chamaesyce using nuclear ribosomal ITS and chloroplast ndhF
sequences, with substantially increased taxon sampling compared to previous studies. Based on the phylogeny, we discuss the
Old World origin of the subgenus, the evolution of cyathial morphology and growth forms, and then provide a formal sectional
classification, with descriptions and species lists for each section or subsection we recognize.
Key Words
C

; CAM; Euphorbia subgenus Chamaesyce; Euphorbiaceae; ITS; ndhF
Supplementary Material
The alignment files are available in the Supplementary Data section of the online version of this article
(http://www.ingentaconnect.com/content/iapt/tax).

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also support the monophyly of four major clades within Eu-
phorbia, which were informally named by Steinmann & Porter
(2002) as clades A, B, C and D. Among them, clade D was later
recognized by Bruyns & al. (2006) as subg. Chamaesyce Raf.
These studies either have limited taxon sampling within subg.
Chamaesyce, or else they have low statistical support within
subg. Chamaesyce. Steinmann & Porter (2002) sampled 82 of
the 600 species in subg. Chamaesyce for nuclear ribosomal in-
ternal transcribed spacer (ITS), among which 40 also had ndhF
sequences. Using maximum parsimony, they found that the
majority of deep nodes within the genus received low statistical
support. Four subsequent genus-wide molecular phylogenetic
studies each added only a small number of species within subg.
Chamaesyce, and relationships among major groups of the sub-
genus remained poorly supported (Bruyns & al., 2006, 2011;
Park & Jansen, 2007; Zimmermann & al., 2010). This problem
was partly addressed by the “backbone” phylogeny of Horn &
al. (2012a), which sampled 176 species across Euphorbia using
ten loci, including nuclear, mitochondrial and chloroplast re-
gions, with 31 representative species within subg. Chamaesyce.
This study had much improved support values within subg.
Chamaesyce, and it highly supported the monophyly of subg.
Chamaesyce, as well as its sister relationship to Euphorbia
subg. Euphorbia. Of all six previous genus-wide molecular
studies, three of them support a monophyletic, primarily New
World clade nested in a basal Old World grade (Steinmann &
Porter, 20 02; Zimmer mann & al., 2010; Horn & al., 2012a). The
other three studies lack statistical support for deep nodes within
subg. Chamaesyce (Bruyns & al., 2006, 2011; Park & Jansen,
2007). In addition to these studies, Yang & Berry (2011) con-
structed a robust phylogeny of Euphorbia subg. Chamaesyce
sect. Anisophyllum, which corresponds to the former segregate
genus Chamaesyce S.F. Gray. In their analysis, 138 ingroup
species were sequenced with two nuclear loci and three chlo-
roplast loci, and the monophyly of sect. Anisophyllum was well
supported. Taking all seven previous molecular studies into
account, about a third of the species in subg. Chamaesyce were
sampled, and most species outside of sect. Anisophyllum only
have ITS sequences available.
With the international collaborative network established
by the Euphorbia Planetary Biodiversity Inventory (Euphorbia
PBI) project (www.euphorbiaceae.org), we have been able to
greatly expand our worldwide taxon sampling to reconstruct a
well-sampled, and well-supported molecular phylogeny. The
main purpose of this paper is to propose a revised sectional and
subsectional classification of Euphorbia subg. Chamaesyce in
light of the updated phylogeny we have produced. This will
provide a stable nomenclatural base for subsequent research.
MaterIals and Methods
Taxon sampling. —
Silica-preserved leaf samples were
collected in all major areas where Euphorbia occurs dur-
ing 2006–2009. Sampling was supplemented by leaf mate-
rials taken from herbarium sheets. To include as many taxa
as possible belonging to subg. Chamaesyce, we conducted a
preliminary maximum parsimony analysis in PAUP* (Swof-
ford, 2003), using ndhF sequences to assign each taxon to one
of the four subgenera in Euphorbia. In addition, all sequences
in GenBank that belong to subg. Chamaesyce were included.
In total, our taxon sampling covered 291 out of the total of
600 species in the subgenus, with all previously recognized
sections and most subsections represented. Since the mono-
phyly and subclade structure within sect. Anisophyllum was
well established in an earlier study (Yang & Berry, 2011), we
reduced taxon sampling within sect. Anisophyllum to 15 species
representing all major subclades. About 80 DNA accessions
that grouped together with conspecific sequences during our
prelimi nar y analysis were excluded. In total, our final matrices
include 174 taxa (163 ingroup taxa and 11 species represent-
ing the other three subgenera of Euphorbia as outgroups). All
taxa sampled for the molecular phylogeny are associated with
herbarium voucher specimens and are listed in the Appendix.
DNA extraction, amplification, and sequencing. —
DNA
extraction and PCR amplification of the ITS region were car-
ried out following Yang & Berry (2011). The chloroplast NADH
dehydrogenase F (ndhF) coding region was PCR-amplified in
two pieces: the 5ʹ half was amplified using primers 536 and
1318R (Olmstead & Sweere, 1994), and the 3ʹ half using prim-
ers 972 (Olmstead & Sweere, 1994) and 2110Ri (Steinmann &
Porter, 2002). The PCR mixture contained 0.15 μL of 5 units/μL
Ex Ta q (Takara Bio Inc., Otsu, Shiga, Japan), 2.5 μL 10× Ex
Taq Buffer, 2.0 μL dNTP (2.5 mM), 1.0 μL of each primer (10
μM), 2 μL of diluted template DNA (dilution varies from 1/20
to 1/80), and ddH

O to bring the final volume to 25 μL. The
PCR profile consisted of an initial 4 min denaturing step at
95°C followed by 40 cycles of 45 s denaturing at 95°C, 45 s
annealing at 53.6°C, and 2 min “slow and cold” extension at
65°C (Shaw & al., 2007). PCR products were purified with
ExoSap-IT (USB Corporation, Cleveland, Ohio, U.S.A.), or
QIAquick PCR Purification Kit (Qiagen, Valencia, California,
U.S.A.). Cleaned PCR products were sequenced at the Univer-
sity of Michigan DNA Sequencing Core using the respective
PCR primers.
Phylogenetic analyses. —
Chromatograms were as-
sembled and edited in the program Sequencher v.4.10.1 (Gene
Codes, Ann Arbor, Michigan, U.S.A.). Sequence alignments
were performed in the program MUSCLE v.3.8 (Edgar, 2004)
using the default parameters, and manually adjusted in the
program MacClade v.4.08 (Si mmons, 2004; Maddison & Mad-
dison, 2005). The full-length data matrices are in the online
supplementary data, and sequences are deposited in GenBank
(Appendix).
Phylogenetic analyses using maximum likelihood (ML)
and Bayesian inference (BI) were conducted on the ITS and
ndhF matrices separately, with gaps treated as missing data.
Congruence between the resulting ITS and ndhF trees was
visually inspected before concatenating them into a combined
matrix. ITS, ndhF and the combined matrices were each sub-
jected to the analyses described below.
Maximum likelihood analyses were carried out in the pro-
gram RAxML v.7.0.3 (Stamatakis, 2006), partitioning ITS vs.
ndhF regions. The nucleotide substitution model was set to

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Fig. 1.
Euphorbia subg. Chamaesyce:
A–E,
representative growth forms;
F–K,
cyathial morphologies;
L–Q,
seed morphologies.
A,
Euphorbia
plagiantha, a broom-like tree (sect. Plagianthae; Do rs ey 164, MICH);
B,
E. burmannii, a stem-succulent shrub with opposite or dichotomous
branching and terminal cymes (sect. Articulofruticosae; Becker & Moller 1141, UNIN);
C,
E. subpeltata, a herb with indeterminate main shoots
and axillary cymes (sect. Alectoroctonum; Steinmann 5585, IEB);
D,
E. gumaroi, a stem-succulent herb with alternate branching and single,
terminal cyathia (sect. Alectoroctonum; Steinmann 5813, MICH);
E,
E. maculata, a prostrate herb with early termination of main shoots typi-
cal of sect. Anisophyllum;
F,
E. guerichiana, showing exappendiculate glands (sect. Espinosae; Becker & Moller 929, U NI N);
G,
E. petiolata,
showing pectinate cyathial glands (sect. Cheirolepidium; Zarre & Salmaki 39514, TUH);
H,
E. eriantha, showing gland appendages arching over
and concealing the glands (sect. Erianthae; field photo, California);
I,
E. subpeltata, showing cyathial appendages with finger-like lobes (sect.
Alectoroctonum; Steinmann 5585, IEB);
J,
E. sphaerorhiza, showing cyathial morphology typical in sect. Alectoroctonum (Yang 110, MICH);
K,
E. heterophylla, showing single, stalked and cupped glands typical of sect. Poinsettia subsect. Stormieae (Riina 1825, VEN);
L,
E. espinosa
(sect. Espinosae; Lea ch 159 38 , UNIN);
M,
E. petiolata (sect. Cheirolepidium; Zarre & Salmaki 39514, TUH);
N,
E. cheirolepis (sect. Cheirolep-
idium);
O,
E. mundii (sect. Articulofruticosae; L eac h 17110 , UNIN);
P,
E. goyazensis (sec t. Crossadenia; Caruzo 139, HUEFS);
Q,
E. sonorae
(sect. Alectoroctonum; Fishb ei n 2455, RSA). — Photo credits: A, B.L. Dorsey; B & F, A. Moller; C, D, I & J, V.W. Steinmann; E, P.E. Berry;
G & M, Y. Salmaki and S. Zarre; H, S. Matson; K, R. Riina; L, O & Q, B. Wagner; N, A.H. Pahlevani; P, J.J. Morawetz.
◄
GTR + G as recommended by the RAxML manual; 500 ML
bootstrap replicates were performed, followed by a thorough
search for the best tree. Bayesian inference was conducted in
the program MrBayes v.3.1.2 (Huelsenbeck & Ronquist, 2001;
Ronquist & Huelsenbeck, 2003). Two independent runs (four
for the combined dataset) of four chains each (three heated, one
cold), starting from random trees, using the default temperature
of 0.2, were run for 15 million generations. Trees were sampled
every 1000 generations. Each analysis was conducted using the
nucleotide substitution model GTR + I + G as selected by Akaike
information criterion (AIC) in the program MrModeltest v.2.3
(Nylander, 2004). To prevent unrealistically long branches, “br
lenspr=unconstrained:exponential(100.0)” was applied (Brown
& al., 2010; Marshall, 2010). The relevant parameters for con-
vergence were visually examined in the program Tracer v.1.5
(Rambaut & Drummond, 2007) to verify stationary status.
Trees from the first 2.5 million generations were discarded as
burn-in; the remaining trees were used to compute the majority-
rule consensus tree and support statistics.
res u lt s
Overall statistics of the gene regions sequenced for this
study are summarized in Table 1. Results of phylogenetic analy-
ses are shown in Figs. 2 and 3 and are summarized in Fig. 4. For
each of the three analyses (ITS, ndhF, combined ITS + ndhF ),
BI and ML results are congruent for nodes with ML bootstrap
support (MLB) ≥ 50 and Bayesian posterior probability (PP)
≥ 0.80; monophyly of subg. Chamaesyce and its sister relation-
ship to Euphorbia subg. Euphorbia are both highly supported
(MLB ≥ 80; PP = 1). Groups are numbered consistently across
Figs. 2–4, and labels for sections, subsections, and subclades
are shown on the combined tree only in Fig. 3.
ITS dataset. —
The ITS dataset has a relatively high pro-
portion of variable sites compared to ndhF (71.1% vs. 45.1%,
Table 1). The alignment required some manual adjustment in
parts, and all characters were included in the subsequent phy-
logenetic analysis. Monophyly of each section is strongly sup-
ported by MLB ≥ 70 (not shown) and PP = 1 (Fig. 2), except
that sect. Gueinziae (11) is nested in sect. Crossadenia (12) with
MLB = 72 (not shown) and PP = 0.81.
ndhF dataset. —
The ndhF coding region could be unam-
biguously aligned, with relatively fewer variable sites compared
to ITS (Table 1). Monophyly of each section is supported by
MLB ≥ 81 (not shown) and PP ≥ 0.88 (Fig. 2), except for sect.
Poinsettia, where E. jaliscensis is sister to sect. Poinsettia (14)
+ sect. Alectoroctonum (15) with MLB = 62 (not shown) and
PP = 0.75 (Fig. 2).
Combined ITS + ndhF dataset. —
Analysis of the combined
dataset produced a well-resolved phylogeny (Fig. 3). Mono-
phyly of each section is supported by MLB ≥ 92 and PP ≥
0.92, except for sect. Crossadenia, which has sect. Gueinziae
nested within it. Relationships within each clade are well re-
solved in general, except for certain nodes in sect. Alectoroc-
tonum and sect. Articulofruticosae. There are five instances of
moderately (thin continuous lines) to strongly supported (thick
lines) incongruence between the ITS and ndhF datasets, and
such incongruences affect the combined analysis in different
ways (Figs. 2, 3). (1) In sect. Alectoroctonum, the two clades
marked with an asterisk ( * ) are strongly supported as sister to
each other in the combined analysis and in the ndhF phylog-
eny, while ITS strongly supports them forming a paraphyletic
grade. (2) Euphorbia jaliscensis is strongly supported as nested
Table 1.
Summary statistics for the aligned molecular data matrices.
ndhF ITS combined ndhF + ITS
No. of accessions 147 172 182
Range of raw length

[bp] 762–1480 336–651 584–2123
Aligned length 1547 714 2261
Variable characters (proportion) 697 (45.1%) 508 (71.1%) 1205 (53.3%)

Lower ends of raw lengths are from partial sequences that the full-length sequences failed to amplify or sequence.

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within sect. Poinsettia in the combined analysis and with ITS,
but not with the ndhF data alone. (3) Euphorbia gueinzii is
nested within sect. Crossadenia in the ITS analysis wit h strong
support, while ndhF provides low support (dashed line) for
E. gueinzii being sister to sect. Crossadenia; the combined
analysis is congruent with the ITS topology in this case but
with weaker support values. (4) Euphorbia salota is strongly
supported by the combined and ndhF analyses to be nested
within the Madagascar clade, while ITS places it sister to sect.
Cheirolepidium + sect. Eremophyton with moderate support,
separated from the rest of the Madagascan species. (5) Within
sect. Articulofruticosae, results from ITS either conflict with
ndhF or are poorly resolved, and the combined tree is also
poorly resolved.
dIscussIon
Our results are consistent with all six previous genus-wide
molecular phylogenetic studies and support subg. Chamaesyce
being monophyletic and sister to subg. Euphorbia (Steinman n
& Porter, 2002; Bruyns & al., 2006, 2011; Park & Jan sen, 2007;
Zimmermann & al., 2010; Horn & al., 2012a). Three of these
six previous studies supported a single origin of New World
taxa from an Old World grade within subg. Chamaesyce, with
the eastern Brazilian clade sect. Crossadenia being sister to
the rest of the New World group (Steinmann & Porter, 2002;
Zimmermann & al., 2010; Hor n & al., 2012a). Our results differ
somewhat in that they support an Old World–eastern Brazilian
clade sister to a New World clade, and together these are nested
in a paraphyletic Old World grade (Fig. 4).
Bruyns & al. (2006) made an attempt to provide a sec-
tional classification of subg. Chamaesyce based on molecular
data. They recognized four sections within the subgenus: (1)
“sect. Chamaesyce”, which included the New World clade + Old
World–eastern Brazilian clade + sect. Ten ell ae, sharing petaloid
cyathial appendages (the “petaloid appendage clade”, Fig. 4;
Horn & al., 2012a); (2) sect. Frondosae, a diverse Old World
group; (3) sect. Articulofruticosae, a group of pencil-stem suc-
culents from southern Africa that is both molecularly and mor-
phologically distinct; and (4) sect. Espinosae, a clade of two
shrubby or tree-forming species from Africa; they left E. tan-
nensis unplaced. Among the four sections that they recogn ized,
we agree with their naming and circumscription for all but the
0.05
scatorhiza
punicea
exilis 2
lumbricalis
gentilis
albipollinifera
spinea
pirottae
herrei
arceuthobioides
breviarticulata
juttae 1
chersina
goetzei
mundii
acanthothamnos
karroensis
barbicollis
platyclada
rhombifolia 2
suffulta
espinosa
einensis
exilis 1
burmannii
aequoris 1
guerichiana
pervilleana
rhombifolia 3
gymnonota
stapelioides
brachiata
phosphorea
parvicaruncula
tannensis subsp. tannensis
caterviflora
juttae 2
aequoris 2
tannensis subsp. eremophila
salota
cheirolepis
royleana
crotonoides
rhombifolia 1
hinkleyorum
ephedroides
bemarahaensis
leistneri
petiolata
agowensis
helioscopia
1
0.82
0.64
0.99
1
1
0.74
0.53
0.9
0.91
1
1
1
1
0.97
0.85
1
1
1
1
0.69
0.98
1
1
1
1
1
0.64
1
1
0.74
1
0.7
1
0.58
0.96
0.98
0.02
barbicollis
punicea
mundii
crotonoides
aequoris 1
royleana
brachiata
acanthothamnos
exilis 2
burmannii 2
espinosa
platyclada
plagiantha
juttae 2
spinea
gentilis
ephedroides
burmannii 1
salota
denisii
juttae 1
gymnonota
tannensis subsp. tannensis
goetzei
pirottae
herrei
polyantha
petiolata
breviarticulata
albipollinifera
spartaria
rhombifolia 3
einensis
helioscopia
planiticola
caterviflora
guerichiana
pervilleana
rhombifolia 2
rhombifolia 1
quaitensis
scatorhiza
chersina
hinkleyorum
leistneri
aequoris 2
giessii
phosphorea
kabridarensis
1
0.88
1
0.98
1
0.54
0.98
1
1
0.77
1
1
1
0.9
1
1
0.99
1
1
1
1
0.64
1
1
0.91
1
1
1
0.77
0.99
1
0.99
1
1
1
1
1
Joins Fig. 2B Joins Fig. 2B
ITS ndhF
5
7
9
1
2
4
5
7
9
1
2
4
3
3
6
8
8
Fig. 2A
Fig. 2.
Majority-rule consensus trees recovered from Bayesian analyses of the nuclear ITS and the chloroplast ndhF coding regions. Numbers be-
low the branches indicate Bayesian posterior probabilities (PP). Thick branches indicate maximum likelihood bootstrap percentages (MLB) ≥ 70
and PP ≥ 0.95, and branches in dashed lines have MLB < 50 and PP < 0.80. Branch length scale on lower left of each tree. Numbers correspond
to numbered sections in Fig. 3 and in the taxonomic treatment. 1 = sect. Espinosae; 2 = sect. Articulofruticosae; 3 = sect. Cheirolepidium; 4 =
sect. Eremophyton; 5 = sect. Scatorhizae; 6 = sect. Denisiae; 7 = sect. Bosseriae; 8 = sect. Plagianthae; 9 = sect. Frondosae; 10 = sect. Tenellae;
11 = sect. Gueinziae; 12 = sect. Crossadenia; 13 = sect. Anisophyllum; 14 = sect. Poinsettia; 15 = sect. Alectoroctonum.

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0.05
scandens
sphaerorhiza 1
sessilifolia
ocymoidea
capitellata
subreniformis
delicatula
flaviana
cotinifolia
bicolor
colorata
crossadenia
xanti
lagunensis
ixtlana
humayensis
oaxacana
sarcodes
guatemalensis
leucocephala
bilobata
ceroderma
corollata
lacera
glanduligera
phylloclada
setosa
guadalajarana
subpeltata
francoana
equisetiformis
radians
lycioides
sp. nov. 2
florida
gumaroi
rzedowski
colletioides
alata
sp. nov. 3
pediculifera
schlechtendalii
chersonesa
arteagae
angusta
exstipulata
fulgens
zonosperma
innocua
segoviensis
eriantha
maculata
acuta
sonorae
sp. nov. 4
whitei
cassythoides
sphaerorhiza 2
acerensis
gueinzii
humifusa
eglandulosa
aaron-rossii
pumicicola
celastroides
sp. nov. 1
graminea
ariensis
guiengola
pulcherrima
strigosa
sp. nov. 5
polyphylla
cornastra
graminea
hindsiana
macropus
thymifolia
caperata
sinaloensis
misera
bifurcata
hirta
poeppigii
gentryi
dioscoreoides
tresmariae
calcicola
soobyi
albomarginata
pinetorum
succedanea
appariciana
rossiana
cuphosperma
mexiaea
sciadophila
setiloba
californica
pentadactyla
cymosa
goyazensis
heterophylla
misella
gradyi
hainanensis
hyssopifolia
gymnoclada
macropodoides
macvaughii
dentata
adiantoides
ipecacuanhae
polygonifolia
hormorrhiza
marginata
antisyphilitica
hexagona
insulana
jaliscensis
cyathophora
1
1
0.97
1
1
0.92
1
0.97
0.97
0.7
0.64
0.81
1
0.59
1
0.98
1
0.98
10.91
0.65
0.53
0.52
1
1
1
1
0.7
0.87
1
1
0.51
1
0.92
1
1
1
1
11
0.84
0.7
1
0.84
1
1
0.99
0.97
1
0.97
1
0.93
0.65
1
1
0.63
0.61
1
0.98
0.97
1
0.83
0.81
0.99
1
0.99
1
1
0.81
1
0.57
1
1
1
1
1
1
1
1
1
1
1
0.64
1
0.83
1
1
0.92
1
1
0.73
0.8
0.98
1
0.99
1
1
1
1
1
1
1
1
1
1
0.99
0.64
1
1
0.99
1
0.02
pediculifera
colletioides
strigosa
misera
exstipulata
alata
insulana
hexagona
dentata
hirta
dioscoreoides
succedanea
thymifolia
setosa
mexiaea
subreniformis
arteagae
scandens
cornastra
bifurcata
misella
phylloclada
goyazensis
pumicicola
hindsiana
delicatula
maculata
humayensis
polygonifolia
pulcherrima
ocymoidea
soobyi
graminea
sp. nov. 5
innocua
radians
xanti
graminea
gumaroi
macropus
marginata
cymosa
eriantha
leucocephala
florida
heterophylla
ceroderma
sonorae
sp. nov. 3
sphaerorhiza 2
subpeltata
bilobata
lycioides
gymnoclada
hormorrhiza
cotinifolia
hyssopifolia
guiengola
macropodoides
oerstediana
corollata
guadalajarana
californica
sphaerorhiza 1
sinaloensis
glanduligera
fulgens
polyphylla
setiloba
antisyphilitica
caperata
sessilifolia
acuta
sp. nov. 2
albomarginata
ixtlana
appariciana
colorata
jaliscensis
sarcodes
cyathophora
chersonesa
sciadophila
francoana
pinetorum
capitellata
cuphosperma
celastroides
gueinzii
sp. nov. 1
xalapensis
tresmariae
angusta
schlechtendalii
sp. nov. 4
gradyi
humifusa
acerensis
1
0.75
0.91
1
1
1
0.85
1
1
1
1
1
0.98
1
0.97
1
1
1
1
1
1
1
0.98
1
1
1
1
1
1
1
1
0.76
0.88
0.88
0.66
1
1
0.82
1
1
0.53
0.61
0.94
0.81
0.75
1
0.62
1
1
0.62
0.99
1
1
1
0.53
0.91
1
1
1
1
0.81
1
1
0.67
0.72
0.83
0.97
1
1
1
0.99
1
0.92
1
0.57
1
1
1
ITS ndhF
Joins Fig. 2A Joins Fig. 2A
*
*
*
*
10
11 and 12
13
14
15
10
12
13
14
15
11
Fig. 2B

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Version of Record (identical to print version).
first one. In that case, we propose that their “sect. Chamae-
syce” needs to be divided into six sections: sect. Tenellae, sect.
Gueinziae, sect. Crossadenia, sect. Anisophyllum, sect. Poin-
settia, and sect. Alectoroctonum. In addition, we designate six
additional Old World sections to accommodate species that were
either unsampled or unplaced by Bruyns & al. (2006), namely,
sect. Cheirolepidium, sect. Eremophyton, sect. Scatorhizae,
sect. Denisiae, sect. Bosseriae, and sect. Plagianthae. In the
following discussion, we focus on comparing our results to the
marker-rich but relatively taxon-poor “backbone” analysis of
Horn & al. (2012a).
The Old World grade. —
In Fig. 4, clades from sect. Espi-
nosae up to sect. Te n ell ae are entirely Old World, forming
the early diverging Old World grade in subg. Chamaesyce.
Within this group, BI analysis of ITS places sect. Eremophy-
ton + sect. Cheirolepidium as sister to the petaloid appendage
clade, similar to the placement in Bruyns & al. (2006), which
was also based on BI of ITS alone (Fig. 2A). However, ML
analysis of ITS, and both BI and ML analyses of ndhF, all
support this clade as sister to the Madagascar clade. The cause
of this incongruence between BI and ML is unknown, but it
could be because BI is more prone to long-branch attraction
(Kolaczkowski & Thornton, 2009).
Our results conflict with those of Horn & al. (2012a)
as to the earliest branching event within the clade of subg.
Chamaesyce (Fig. 4). Our combined analysis recovered sect.
Fig. 3.
Majority-rule consensus tree recovered from Bayesian analyses of the combined dat aset (I TS + ndhF ) with desig nated names of ta xonomic
units. Numbers above the branches indicate maximum likelihood bootstrap percentages (MLB), and numbers below the branches are Bayes-
ian posterior probabilities (PP). Thick branches indicate MLB ≥ 70 and PP ≥ 0.95, and branches in dashed lines have MLB < 50 and PP < 0.80.
Branch length scale on lower left. Numbers next to each section correspond to numbers in Fig. 2 and in the taxonomic treatment. Subgroups
within sect. Alectoroctonum are indicated with hyphenated numbers.
0.03
rhombifolia 1
juttae 1
hainanensis
goyazensis
gueinzii
planiticola
guerichiana
ephedroides
lumbricalis
goetzei
petiolata
polyantha
brachiata
glanduligera
tannensis subsp. eremophila
platyclada
burmannii 1
giessii
juttae 2
hinkleyorum
rhombifolia 2
scatorhiza
punicea
phosphorea
burmannii 2
exilis 2
flaviana
sessilifolia
helioscopia
rhombifolia 3
gentilis
sarcodes
lycioides
aequoris 2
salota
bemarahaensis
spinea
espinosa
einensis
stapelioides
phylloclada
breviarticulata
denisii
pirottae
agowensis
caterviflora
crotonoides
albipollinifera
pervilleana
parvicaruncula
kabridarensis
appariciana
leistneri
chersina
gymnoclada
tannensis subsp. tannensis
exilis 1
barbicollis
herrei
crossadenia
quaitensis
arceuthobioides
suffulta
plagiantha
aequoris 1
mundii
acanthothamnos
spartaria
royleana
gymnonota
cheirolepis
1
1
0.74
0.97
1
0.66
1
1
0.72
0.73
1
0.97
1
0.75
0.7
1
0.98
1
1
1
1
1
0.85
1
1
0.53
0.92
1
1
1
1
1
1
1
0.95
0.99
1
1
0.75
1
1
0.78
1
0.51
1
1
0.65
1
1
0.79
1
1
1
0.8
1
100
98
100
96
60
98
100
81
82
50
100
95
100
81
97
100
100
98
100
95
73
100
99
68
100
99
100
92
Joins Fig. 3B
100
--
100
85
57
100
70
78
100
63
100
100
95
73
99
77
100
100
85
100
--
--
--
--
--
100
sect. Crossadenia (12)
sect. Tenellae (10)
sect. Scatorhizae (5)
sect. Cheirolepidium (3)
sect. Articulofruticosae (2)
sect. Espinosae (1)
sect. Eremophyton (4)
sect. Frondosae (9)
sect. Plagianthae (8)
sect. Denisiae (6)
sect. Bosseriae (7)
subg. Euphorbia
subg. Rhizanthium
subg. Esula
subsect. Apparicianae
subsect.
Sarcodes
sect. Gueinziae (11)
Petaloid
appendage clade
Madagascar
clade
ITS + ndhF
Fig. 3A

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61 (4) • August 2012: 764–789
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macropus
ceroderma
thymifolia
rossiana
celastroides
graminea 1
sciadophila
sphaerorhiza 2
lagunensis
fulgens
pulcherrima
guatemalensis
cuphosperma
subreniformis
capitellata
calcicola
sonorae
innocua
setosa
humifusa
pumicicola
poeppigii
bicolor
gentryi
sphaerorhiza 1
florida
scandens
sp. nov. 5
sp. nov. 3
guiengola
gradyi
acuta
pentadactyla
segoviensis
cassythoides
sinaloensis
lacera
macropodoides
rzedowskii
californica
bilobata
sp. nov. 4
polygonifolia
ocymoidea
insulana
bifurcata
zonosperma
gumaroi
angusta
delicatula
dioscoreoides
aaron-rossii
schlechtendalii
acerensis
pinetorum
maculata
subpeltata
misera
setiloba
xalapensis
whitei
succedanea
hyssopifolia
cymosa
antisyphilitica
pediculifera
soobyi
dentata
xanti
hormorrhiza
sp. nov. 1
corollata
guadalajarana
equisetiformis
oerstediana
strigosa
polyphylla
ixtlana
albomarginata
cotinifolia
hexagona
chersonesa
sp. nov. 2
mexiaea
tresmariae
cyathophora
oaxacana
francoana
ariensis
arteagae
macvaughii
colletioides
marginata
adiantoides
humayensis
colorata
heterophylla
ipecacuanhae
leucocephala
exstipulata
caperata
jaliscensis
radians
cornastra
graminea 2
eglandulosa
hindsiana
hirta
alata
misella
eriantha
1
1
1
1
0.73
0.71
0.9
1
1
1
0.86
1
0.7
1
0.62
0.63
1
0.82
1
1
1
1
1
1
1
1
0.99
1
1
1
1
1
1
0.87
0.87
1
1
1
1
1
1
0.73
0.98
0.98
1
0.91
0.97
1
1
0.81
0.89
1
0.96
1
1
0.99
0.84
1
0.75
1
1
1
1
1
1
0.94
0.87
1
0.98
0.9
1
1
1
0.74
0.74
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0.56
0.98
1
1
1
1
1
1
1
0.97
1
1
0.5
0.89
0.61
74
52
56
100
100
100
98
86
92
92
98
100
93
95
89
85
100
100
100
97
89
98
100
98
99
98
100
99
--
--
--
--
--
100
66
100
100
94
90
59
83
100
79
84
100
100
55
95
62
99
98
100
80
90
99
100
100
100
54
100
83
83
99
100
51
100
100
77
90
98
96
100
85
100
78
99
98
85
100
100
100
100
100
60
94
50
100
100
100
100
100
100
52
92
96
100
100
89
--
--
--
--
--
--
15-8
15-7
15-6
15-5
sect.
Alectoroctonum (15)
sect. Poinsettia (14)
subsect. Exstipulatae
subsect. Lacerae
subsect. Erianthae
sect. Anisophyllum (13)
subsect.
Hypericifoliae
subsect. Acutae
15-12
15-9
Joins Fig. 3A
*
*
subsect. Stormieae
15-10
15-2
15-4
15-3
15-1
15-13
0.03
ITS + ndhF
15-11
Fig. 3B

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Articulofruticosae + sect. Espinosae as sister to the rest of the
subgenus with moderate support. However, Horn & al. (2012a)
recovered sect. Cheirolepidium + sect. Eremophyton + sect.
Scatorhizae + the Madagascar clade + sect. Frondosae as sis-
ter to the rest of subg. Chamaesyce. The latter received much
stronger statistical support and may be more accurate because
of their deeper molecular sampling.
Our results also disagree with Park & Jansen’s (2007)
placement of E. cuneata. The E. cuneata sequence retrieved
from GenBank (specimen/voucher Park 24023) was nested in
our sect. Scatorhizae (not shown). However, our own field-
collected sample of E. cuneata is placed within Euphorbia
subg. Rhizanthium (Riina & al., in prep.), as was another collec-
tion sequenced by Bruyns & al. (2011). Park & Jansen’s (2007)
E. cuneata has the same sequence as the E. polyantha ndhF se-
quence by Steinmann & Porter (2002), except that Park’s ndhF
sequence has a 9-bp deletion in the middle. Because of this, we
believe that Park & Jansen (2007) misidentified E. polyantha
as E. cuneata in their paper.
Among the ten sections we recognize in the Old World
grade, sect. Tenellae is of particular interest because some of
its members share petaloid gland appendages (though they are
vestigial or absent in some species—see later descriptions) with
the Old World–eastern Brazilian clade + the New World clade.
Petaloid appendages (Fig. 1I–J) likely evolved in the common
ancestor of sect. Tenellae + Old World–eastern Brazilian clade
+ the New World clade, and together they form the “petaloid
appendage clade” (Fig. 4; Horn & al., 2012a), which also corre -
sponds to the “Agaloma alliance” of Steinmann & Porter (2002).
The Old World– eastern Brazilian clade. —
With substan-
tially increased taxon sampling compared to all previous stud-
ies, our analyses recovered two Old World species, E. hainan-
ensis Croizat and E. gueinzii Boiss., that group together with
the Brazilian sect. Crossadenia rather than with any other Old
World group (Figs. 2, 3). However, we still consider the posi-
tion of E. hainanensis to be doubtful. It is a shrub endemic
to Hainan Island of southern China, and it is distinctive in
having three cyathial glands and has been postulated to be
closely related to species from tropical Australasia that belong
to Euphorbia subg. Euphorbia (Croizat, 1940; Dorsey & al.,
subm.). This is a rare island endemic species, and we were
only able to obtain a single ITS sequence. On the other hand,
the placement of E. gueinzii is more reliable, with both ITS
and ndhF sequences placing it close to sect. Crossadenia. The
phylogenetic placement of a separate accession of E. gueinzii,
sequenced for ITS at the Smithsonian Institution, was congru-
ent with our results (K.J. Wurdack, pers. comm.).
Although ITS data places E. gueinzii within sect. Cross-
adenia with moderate support, ndhF data moderately supports
its sister relationship to sect. Crossadenia. The combined
analysis places it within sect. Crossadenia, but the support for
this is weak. Because of its distinctive morphology and widely
disjunct South African distribution compared to the otherwise
entirely Brazilian sect. Crossadenia, the ndhF placement is
more likely to reflect the relationships of E. gueinzii. Conse-
quently, we propose a new section for E. gueinzii, based on its
position as sister to sect. Crossadenia in the ndhF tree. In the
case of the enigmatic E. hainanensis, we leave it unplaced unt il
more data are available.
Given the pattern of distribution summarized in Fig. 4 and
the postulated age of Euphorbia (36 Ma) that would exclude
Gondwa nan vicariance (Br uyns & al., 2011), a possible biogeo-
graphic scenario is that New World groups in subg. Chamae-
syce did not have a single origin from the Old World, but that
sect. Crossadenia became established in Brazil first, and then
there was a separate introduction accounting for the rest of the
New World clade. Alternatively, there could have been a single
long-distance dispersal from the Old World to the New World,
followed by back-dispersal to the Old World. It is unclear which
scenario is more likely until further information on E. gueinzii,
E. hainanensis and their close relatives is available.
The (largely) New World cla de. —
Sister to the Old World–
eastern Brazilian clade is a largely New World clade of more
than 500 species. This mainly New World clade consists of
three major subclades [1(2,3)]: (1) Section Anisophyllum is dis-
tinctive in being mostly C

and having a specialized growth
form with early abortion of the main shoot. It is most preva-
lent in warm, semi-desert regions and disturbed areas world-
wide, with its greatest diversity in the New World. (2) Section
Poinsettia is characterized by reduction or loss of petaloid
Fig. 4.
Cladograms comparing major clades from this study and the “backbone” phylogeny (Horn & al., 2012a). Numbers above the branches
indicate maximum likelihood bootstrap percentages (MLB), and numbers below the branches are Bayesian posterior probabilities (PP). Thick
branches indicate MLB ≥ 70 and PP ≥ 0.95, and branches in dashed lines have MLB < 50 and PP < 0.80.
100
86
100
77
99
100
100
66
85
1
1
1
1
1
0.96
0.96
0.95
--
Outgroup
sect. Crossadenia + sect. Gueinziae
sect. Tenellae
sect. Espinosae
Madagascar clade
sect. Scatorhizae
sect. Frondosae
99
50
100
68
81
82
--
1
1
1
0.72
0.78
0.66
0.95
sect. Articulofruticosae
sect. Cheirolepidium
sect. Anisophyllum
sect. Alectoroctonum
Outgroup
sect. Poinsettia
100
1
78
0.73
85
0.99
Old World - Eastern Brazil
Old World
New World
sect. Eremophyton
100
1
sect. Crossadenia
sect. Tenellae
sect. Anisophyllum
sect. Alectoroctonum
sect. Poinsettia
sect. Espinosae
sect. Articulofruticosae
Madagascar clade
sect. Scatorhizae
sect. Frondosae
sect. Eremophyton
Petaloid
appendage
clade
Petaloid
appendage
clade
This study
Horn & al., 2012a

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61 (4) • August 2012: 764–789
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gland appendages and the development of brightly colored
leafy bracts subtending congested terminal synflorescences,
with the whole structure resembling a large blossom. It oc-
curs mainly in forests and desert scrub of subtropical North
America. (3) Section Alectoroctonum corresponds largely to
the former subg. Agaloma (Raf.) House and is predominantly
composed of herbs and shrubs, but also has some pencil-stem
succulents with CAM photosynthesis. All species in this group
have petaloid cyathial gland appendages, and sometimes they
are quite showy. This group occurs in desert scrub to moist
montane forests and prairies in subtropical to temperate areas
throughout the Americas.
Within this New World clade there has been a consider-
able divergence of classification schemes. Bruyns & al. (2006)
opted to lump the entire “petaloid appendage clade” into a
single section “Chamaesyce ”. On the other hand, within the
New World clade alone, there are three well-supported clades,
each or part of which have been treated previously at the rank
of subgenus or even genus (e.g., “Chamaesyce ”, “Poinsettia ”,
and “Agaloma ”; see Dressler, 1961; Koutnik , 1984; Ward, 2001).
If we were to follow this tendency and recognize genera or
subgenera here, we would have to break up groups in the Old
World grade into separate genera or subgenera as well in order
to preserve monophyly. Instead, we choose to recognize three
sections within the New World clade: sect. Poinsettia, sect.
Anisophyllum, and sect. Alectoroctonum.
● Section Poinsettia. – In view of our molecular results and
a re-evaluation of the morphological characters of the group, we
propose a broader circumscription of sect. Poinsettia compared
to the previous treatments by Dressler (1961) and Mayfield
(1997). These authors restricted the application of the name
“Poinsettia ” to what we recognize here as subsect. Stormieae
Croizat, namely those species with deeply cup-shaped involu-
cral glands that lack petaloid appendages and are usually one
or few in number (Fig. 1K). Other characteristic features com-
monly found in these species include colored bracts subtending
the congested terminal cymes; pandurately lobed to linear,
often heteromorphic leaves with at least some serration on the
margins; glandular stipules; and coarsely tuberculate seeds,
sometimes with a deeply sunken caruncular facet.
The three other subsections that we recognize in sect. Poin-
settia are successively sister to subsect. Stormieae, beginning
with subsect. Exstipulatae, followed by subsect. Erianthae, and
then subsect. Lacerae (Fig. 3B). These three subsections all have
some kind of involucral gland appendage, but that character is
variable within the entire section, and two species nested in
subsect. Stormieae, E. chersonesa and E. cornastra, have been
reported to have a rudimentary appendage on the outer lip of the
glands (Huft, 1984; Mayfield, 1997). In the case of E. bifurcata,
which is placed here in subsect. Exstipulatae, it would be an
otherwise indistinguishable member of subsect. Stormieae if
not for the whitish appendage of its usually single cupular gland.
Except for E. eriantha, which was placed by Boissier (1862) in
sect. Poinsettia, the species in the three new subsections pro-
posed here were previously included in sect. Zygophyllidium
(Boissier, 1862; Dressler, 1961; Huft, 1984), which is included
within sect. Alectoroctonum in our classification.
In addition to the molecular evidence, which strongly sup-
ports the monophyly of an expanded sect. Poinsettia (PP 1;
MLB 100), there are morphological characters that support
the inclusion of the additional species in sect. Poinsettia, and,
conversely, their exclusion from sect. Alectoroctonum. First are
the serrate leaf margins, which are evident in all species of sect.
Poinsettia, except E. pinetorum, E. colorata, E. restiacea (all
in subsect. Stormieae), and E. eriantha (subsect. Erianthae),
although teeth can usually be seen in the latter two species
under magnification. These four species all have linear leaves,
and their teeth may have become inconspicuous or obsolete as
the leaves became narrower. On the other hand, serrate leaves
are very rare in sect. Alectoroctonum. Both species of sub-
sect. Lacerae, which is sister to the other three subsections of
sect. Poinsettia, have serrate, heteromorphic and/or pandurate
leaves, which are usually considered to be hallmarks of sect.
Poinsettia s.str. The feathery gland appendages of subsect.
Erianthae (Fig. 1H) are unique in the genus and bear little
resemblance to any of those in sect. Alectoroctonum. Likewise,
the two-horned gland appendages in E. lacera are very dif-
ferent from the petaloid appendages in sect. Alectoroctonum.
Another factor that may have confounded the recognition
of an expanded sect. Poinsettia distinct from sect. Alectoroc-
tonum in the past was the erroneous placement of E. bilobata
in sect. Poinsettia in the molecular phylogeny of Steinmann
& Porter (2002). Euphorbia bilobata is a true member of sect.
Alectoroctonum, as shown by its placement in this study close
to E. hexagona (the type species of Boissier’s sect. Zygophyl-
lidium; Fig. 3B); a review of its morphological features shows
that they are fully consistent with its placement in sect. Alec-
toroctonum. Thus the position of E. bilobata in Steinmann &
Porter (2002) was likely due to an error.
In summary, we see no overriding morphological conflicts
with sect. Alectoroctonum in expanding the circumscription of
sect. Poinsettia to include the five additional species in three
subsections recognized here. Within the context of the “petaloid
appendage clade” (Horn & al., 2012a) to which sect. Poinsettia
belongs, it is not surprising that the earliest diverging subsec-
tions in section Poinsettia would have petaloid appendages
and that these were subsequently lost in subsect. Stormieae.
● Section Anisophyllum. – Boissier (1862) proposed eight
subdivisions within sect. Anisophyllum. Since then, due to the
relatively homogenous morphology and wide distribution of
this group, Boissier’s classification scheme remained largely
unchanged except for some minor modifications (Binojkumar
& Balakrishnan, 2010). Yang & Berry’s (2011) analyses of
chloroplast markers strongly supported three major subclades
within sect. Anisophyllum [1(2,3)]: (1) the Acuta clade, with
only three species endemic to southwestern U.S.A. and north-
ern Mexico that have C

and C

photosynthesis and glandular
stipules; (2) the Peplis clade, consisting of mainly glabrous,
perennial herbs wit h entire leaf margins that all have C

photo-
synthesis and mostly endemic to the southwester n U.S.A. and
northern Mexico; and (3) the Hypericifolia clade, consisting
of annual and perennial herbs to woody perennials, often with
toothed leaf margins and usually with some kind of pubes-
cence, distributed worldwide, and which are also all C

. Since

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no character or character sets can readily distinguish species
in the latter two clades, and nuclear markers indicate that there
has been widespread reticulate evolution among members of
these two clades, here we only recognize two subsections in
subsect. Anisophyllum: the Acuta clade constituting subsect.
Acutae, and all remaining species comprising subsect. Hy-
pericifoliae.
● Section Alectoroctonum. – Classification within sect.
Alectoroctonum is difficult due to its diversit y of grow th forms
and the incompletely resolved phylogeny we obtained. Shrubs
have evolved several times from herbaceous ancestors (Horn &
al., 2012a), and mor pholog ically similar species repeatedly tur n
out to belong to distinct groups in our molecular phylogeny. In
addition, the majority of the deep branches in the section are
short and are poorly or only moderately supported (Fig. 3B),
and some well-supported branches conflict among markers
(Fig. 2B). Between our ITS and ndhF results (Fig. 2B), the two
clades marked with an asterisk are sister to each other in the
ndhF analysis but form a grade in the ITS analysis, with each
placement being well-supported. Additional gene regions such
as nuclear ribosomal ETS, chloroplast matK, and the nuclear
low-copy coding region exon 9 of EMB2765 revealed even
more extensive conflicts among well-supported clades (data
not shown). Therefore, additional markers, expanded taxon
sampling, and careful morphological studies are needed to bet-
ter resolve relationships within sect. Alectoroctonum and to
formally circumscribe subsections. Here we discuss informal
species groups that are well supported by both morphological
and molecular data, and then point out ambiguities that will
require further investigation.
Clades 15-1 to 15-4 together form the basal grade of sect.
Alectoroctonum (Fig. 3B). The majority of species in th is grade
occupy mid-elevation pine-oak forests in Mexico, while clade
15-1 and E. acerensis of clade 15-3 occur in the Caribbean and
South America. Euphorbia graminea, also part of clade 15-3,
is a widespread and variable species across warm regions of
North and South America. Species in clade 15-1 are distinctive
in having only two glands per cyathium (sometimes three in
E. insulana). Clade 15-2 is endemic to Mexico and has distinc-
tive globose-tuberous roots (Huft, 1979). However, E. macro-
pus, which is another Mexican species with globose roots, is
placed in clade 15-4 in our analysis, and it indeed shares mor-
phological characters with both clade 15-2 and 15- 4. Clade 15-3
is distinctive in having stalked glands and four or five glands
per cyathium (sometimes also two or three in E. graminea); leaf
shape is highly variable, and leaf margins are sometimes sinu-
ate, instead of being entire as in most of sect. Alectoroctonum.
Both E. graminea and E. ariensis share white, showy bracts.
Euphorbia graminea is very similar to both species of clade 15-1
in gross morphology, but it differs from them in having glabrous
in stead of densely pubescent capsules (Ward, 2001). Euphorbia
graminea is the type of sect. Cyttarospermum Boiss., but other
species that were placed in that section by Boissier (1862) are
spread over many separate clades within sect. Alectoroctonum.
Species in clade 15-4 are characterized by opposite leaves and
branches, four or five glands per cyathium, green gland append-
ages, and all are confined to Mexico.
Euphorbia misella appears in an isolated position, sister to
clades 15-5 to 15-8 (Fig. 3B). It is a tiny fall annual herb native
to high elevation pine-oak forests in Mexico. It is very similar
to E. sinaloensis and E. succedanea of clade 15-5 in morphol-
ogy, growth form, habitat and distribution. However, these
three Mexican annuals do not form a monophyletic group in
our analysis. Clade 15-5 contains mostly shrubs. Species from
E. misera to E. californica have alternate branches and spirally
arranged leaves on short shoots, and they all occur in desert
scrub of the Sonoran Desert. In contrast, species from E. cotini-
folia to E. macvaughii have verticillate leaves and branches
and occupy tropical forests from Mexico to South America.
Clade 15-6 corresponds to subsect. Petaloma R af. ex Pax; both
E. marginata and E. bicolor are annual herbs that are widely
cultivated as ornamentals for their showy, white-margined
bracts. Clade 15-7 corresponds to sect. Arthro thamnus sub-
sect. (noted as “ § ” in Boissier, 1862) Americanae Boiss., and is
characterized by dioecious pencil-stem shrubs, with opposite or
whorled, ridged branches; the leaves are scale-like or caducous,
and they lack stipules. Both E. alata and E. cassythoides occur
in the Greater Antilles (Cuba and Jamaica, respectively). The
closely related Galápagos endemic E. equisetiformis is also a
leafless opposite-stemmed shrub, yet these three species do
not form a monophyletic group in our analyses. Euphorbia
innocua occurs in an isolated position sister to clade 15-8; it is
a prostrate herb with four glands that superficially resembles
sect. Anisophyllum; it was treated by Webster (1967) as the
sole representative of sect. Tithymalopsis subsect. Innocuae
G.L. Webster. Webster (1967) considered it to be intermedi-
ate between sect. Alectoroctonum and sect. Anisophyllum, but
such a relationship is not supported by our analyses. Clade
15-8 largely corresponds to sect. Tithymalopsis subsect. Ipe-
cacuanhae Boiss. (Huft, 1979; Holmgren & Holmgren, 1988).
It represents the northernmost distribution for sect. Alecto-
roctonum, extending from the eastern United States north to
southern Canada. Species in this group are perennial herbs
with leaves that are rounded at the apex and with ovoid seeds
that are rounded in cross-section, smooth or shallowly pitted
on the surface, and lacking a caruncle (Huft, 1979).
Both species in clade 15-9, E. leucocephala and E. cape-
rata, are shrubs with verticillate leaves and five involucral
glands (Fig. 3B). They differ from other shrubs of sect. Alec-
toroctonum in having showy, entirely white bracts. Both spe-
cies have carunculate seeds, which is otherwise rare in sect.
Alectoroctonum. Clade 15-10 includes three species that are
densely branched pencil-stem shrubs with a waxy surface,
with cyathia in axillary cymes, five involucral glands with
well-developed appendages, and seeds that are ovoid with a
smooth surface. Between clades 15-10 and 15-11, there are two
species that form part of a polytomy and whose exact affini-
ties are unclear. One of these, E. fulgens (“scarlet plume”), is
cultivated for its large and showy gland appendages. In the
weakly supported clade 15-11, E. bilobata and E. hexagona
both have only opposite leaves and branches and were formerly
treated as part of sect. Zygophyllidium Boiss. The remain-
ing species of sect. Zygophyllidium as defined by Boissier
(1862) are scattered in other parts of sect. Alectoroctonum

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and in sect. Poinsettia in our analyses. The other two species
of clade 15-11, E. soobyi and E. segoviensis, are morphologi-
cally consistent with clade 15-13 and may prove to belong to
that clade with additional data. Clade 15-12 includes shrubs
with verticillate leaves and branches, deciduous leaves, and
cyathia that are clustered in dense cymes and have five or six
cyathial glands. Between clades 15-12 and 15-13, E. gumaroi
is a small succulent, decumbent species that was compared to
E. antisyphilitica in its original description (Meyrán García,
2000), but such an affinity is not supported by our molecular
data. Cyathia in E. gumaroi are single and ter m inal rather than
in axillary cymes as in E. antisyphilitica. Finally, clade 15-13
is a group of about 25 species of herbs and shrubs from warm
parts of North and South America. Some species in this clade
were treated as part of sect. Cyttarospermum Boiss. (Boissier,
1862), but the type of that section (E. graminea) belongs in
clade 15-3. Species in clade 15-13 are characterized by hav-
ing petioles that are longer than the leaf blades, five cyathial
glands, often deeply lobed gland appendages, and ecarunculate
seeds that are deeply pitted, with protrusions on distinctive
honeycombed ridges (Fig. 1Q).
Evolution of growth forms and photosynthetic types.
—
The basic structure of a Euphorbia plant is shown in Fig.
5A. Annual members of the genus best exemplify this architec-
ture, as various parts of the plant may die back in perennials.
Distal to the cotyledonary node, the plant sometimes develops
nodes with opposite leaves and side branches. Further up the
main shoot, both leaves and branches switch to being alter-
nate. Either, neither, or both of the opposite/alternate vegetative
sections can be absent. Later, the main shoot terminates with
a whorl of leaves and usually an equal number of branches,
concomitant with a switch to reproductive growth, which is
typically a pleiochasium of cymes. In this scheme, the synflo-
rescence in Euphorbia typically has three levels of organization
(Fig. 5A): (1) the cyathium itself bearing tightly packed male
and/or female flowers, (2) the cyathia arranged in cymes, and
(3) the cymes arranged in pleiochasia at the point of apical ter-
mination of the main stem. Despite various terminologies that
have been applied to these three organization levels, here we
call the leaves (or bracts when they are not green) that directly
subtend a single cyathium “subcyathial bracts”, leaves/bracts
at lower nodes of the synf lorescence “dichasial bracts”, and
the lowest whorl of leaves associated with the synflorescence
“pleiochasial bracts” (Fig. 5A; Molero & Rovira, 1992).
One notable modification of the basic plant structure in
Euphorbia is the lack of apical grow th of the main shoot (Figs.
1E, 5B; Hayden, 1988). This growth form is a synapomorphy
for sect. Anisophyllum, in which essentially the entire plant
body resembles a synflorescence. Together with juvenile flow-
ering, copious seed production, and C

photosynthesis, sect.
Anisophyllum has been very successful in colonizing warm
and semi-desert areas and disturbed habitats worldwide. How-
ever, both E. remyi and E. halemanui, two ascending shrubs
endemic to the Hawaiian Archipelago, develop main shoots
with continued apical growth and opposite leaves (Koutnik,
1987). In E. potentilloides, and occasionally in E. angusta and
E. viscoides, the annual growth terminates in a whorl of three
or more leaves before producing the terminal synflorescence
(Simmons & Hayden, 1997).
Another notable example of modification in growth form
is the continued elongation of main shoots with alternate or
verticillate leaves and branches (Fig. 5C). In this growth form,
cyathial cymes are axillary instead of arranged in a terminal
whorl. This type is seen in all members of clades 15-12 and
most of 15-13 of sect. Alectoroctonum (Figs. 1C). A further
modification of this growth form occurs when stems become
fleshy and photosynthetic, and leaves are deciduous or re-
duced; then the plants become stem succulents with alternate
Fig. 5.
Diversity of growth forms in Euphorbia subg. Chamaesyce.
A,
The basic growth form variations in Euphorbia, with the three synflores-
cence organization levels (Wheeler, 1941: pl. 655; Molero & Rovira, 1992).
B–E,
Modifications of the basic growth form:
B,
early termination
of the main shoot;
C,
main shoot indeterminate and cymes axillary;
D,
similar to C but stems become succulent; and
E,
stem succulents with
terminal cymes.
Cotyledons
Opposite leaves and side branches
(may be absent)
Alternate leaves and side branches
(may be absent)
Shoot terminates with a whorl of
pleiochasial bracts and branches
Subcyathial bracts
Dichasial bracts
AB
ED
C
Organization level 3:
pleiochasium of cymes
Organization level 1:
cyathium of flowers
Organization level 2:
cymes of cyathia

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branching and axillary cyathia or cyathial cymes (Figs. 5D).
This type of growth form is seen in sect. Plagianthae (E. pla-
giantha, Fig. 1A) and sect. Alectoroctonum (all members of
clade 15-10, and E. gradyi of clade 15-13).
A second ty pe of stem succulence of sepa rate origi n occurs
when the main shoot terminates with a pleiochasial cyme, and
both the vegetative section and the synflorescence (except for
the cyathia themselves) become succulent. This way the plants
have mostly dichotomous or whorled branching, with termi-
nal cyathia or cyathial cymes (Fig. 5E). This growth form is
found in all species of sect. Articulofruticosae (Fig. 1B), sect.
Bosseriae, part of sect. Crossadenia (subsect. Apparicianae +
E. gymnoclada), and part of sect. Alectoroctonum (clade 15-7
+ E. equisetiformis). Perhaps a third type of succulent growth
form is evident in Euphorbia gumaroi, which is a Mexican
member of sect. Alectoroctonum that is unique in having alter-
nate succulent branches with single, terminal cyathia (Fig. 1D;
Meyrán García, 2000).
Euphorbia is extremely diverse in succulent growth
forms, and most of the diversity in succulence is found in subg.
Euphorbia and subg. Rhizanthium. Still, in subg. Chamaesyce,
stem succulence has evolved at least six times, with multiple
origins in both the Old World (southern Africa, Madagascar)
and the New World (eastern Brazil, North America). Occur-
rences of stem succulence are usually associated with CAM
photosynthesis. Stable isotope ratios (δ13C) have been tested
in sect. Articulofruticosae, within which both E. ephedroides
and E. rhombifolia have values ty pical of CAM plants. In sect.
Bosseriae, E. platyclada was tested for δ13C and has a typical
CAM value; in sect. Crossadenia, E. appariciana has a ratio
consistent with weak or facultative CAM expression; and in
sect. Alectoroctonum, E. ceroderma (clade 15-10) has a value
consistent with CAM photosynthesis (Horn & al., 2012b).
Conclusions. —
Euphorbia subg. Chamaesyce has been
recircumscribed here based on molecular data. With taxon
sampling covering nearly half of the ingroup species and a
well-resolved phylogeny, we can now begin to understand evo-
lutionary trends in a worldwide lineage with diverse growth
forms and photosynthetic types. In the following treatment, we
circumscribe fifteen sections that are each morphologically and
geographically distinctive. This updated sectional and subsec-
tional classification of subg. Chamaesyce includes descriptions
and lists of accepted species for each section or subsection.
taxonoMIc treatMent
Species with molecular sequence data available in Gen-
Bank, either published here or previously, are shown in bold in
the “Included species” lists under each section or subsection.
A searchable and downloadable list of accepted names, their
synonymies, type information and distribution for Euphorbia is
available online at http://app.tolkin.org/projects/72/taxa (Riina
& Berry, 2012).
Euphorbia subg. Chamaesyce Raf. in Amer. Monthly Mag.
& Crit. Rev. 2: 119. 1817 – Lectotype: E. supina Raf.
(= E. maculata L.), designated by Wheeler in Contr. Gray
Herb. 127: 59. 1939.
Rafinesque did not include E. chamaesyce L. in his cir-
cumscription of the subgenus, therefore Art. 22.6 of the ICBN
does not apply here.
Annual or perennial herbs, shrubs or trees; rarely geo-
phytes. Stems and leaves sometimes more or less fleshy to
succulent, but not cactus-like. Taproot slender or variously
thickened, cylindrical to globose. Branches few to many,
prostrate, decumbent, or upright; alternate, opposite and/or
ternate; sometimes the apices become spine-like. Leaves alter-
nate, opposite and/or ternate, glabrous or variously pubescent,
sometimes dark green veins visible on species with C

photo-
synthesis; stipules glandular, linear, subulate, triangular, or
inconspicuous. Cyathia bisexual, rarely unisexual, solitary or
in cymes, axillary or terminal, sometimes subtended by green
or brightly colored bracts, actinomorphic or slightly zygomor-
phic; glands (1–)4–5(–7), often with petaloid appendages, less
often appendages horn-like, linear, or missing; ovary glabrous
or pubescent; styles 3, connate or free at the base, bifid or
entire. Capsules 3-lobed or less often subglobose. Seeds ovoid
or oblong, 4-angled, less often 3-angled or rounded in cross-
section; surface variously sculptured or smooth, carunculate
or ecarunculate.
Discussion. – Within Euphorbia subg. Chamaesyce, a total
of 566–574 (see discussion for sect. Articulofruticosae) spe-
cies are recognized and distributed among 15 sections, with
E. hainanensis Croizat sampled but left unplaced as to sec-
tion. There are another 20 or so species in the process of being
formally described, and there are still some unplaced species
in Euphorbia that may prove to belong to this subgenus with
further study.
Due to the high level of homoplasy of morphological char-
acter states in Euphorbia (Horn & al., 2012a), a key to the
sections of subg. Chamaesyce that is of practical value needs
to begin with the entire genus, in which sections can be keyed
out directly instead of keying to the subgenera first. Since the
taxonomic revisions for the other three subgenera are in dif-
ferent stages of completion, it would be premature to attempt
such a key at this point.
1. Euphorbia sect. Espinosae Pax & K. Hof fm. in Engler, Veg.
Erde 9 [Pflanzenw. Afrikas] 3, 2: 149. 1921 ≡ Euphorbia
subsect. Espinosae (Pax & K. Hoffm.) Pax & K. Hoffm.
in Engler & Prantl, Nat. Pflanzenfam., ed. 2, 19c: 213.
1931 – Type: E. espinosa Pax.
Shrubs to small trees, stems with a shiny or papery bark,
the stem apices often drying and becoming spine-like. Leaves
alternate, shortly petiolate; stipules glandular, conspicuous.
Cyathia bisexual, solitary, axillary, subsessile, or on lateral
short shoots, surrounded at the base by a cluster of small leaf-
like or scarious bracts; glands 5, entire, yellow-green, exap-
pendiculate (Fig. 1F); ovary subtended by a 3-lobed perianth;
styles joined at the base, with spreading, bifid apices. Capsules
well-exserted on a reflexed pedicel, deeply 3-lobed, glabrous.
Seeds ovoid, slightly dorsiventrally compressed, smooth, with
a cap-like caruncle.

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Distribution and habitat. – Southern and eastern Africa
(Angola, Botswana, Namibia, northern South Africa, Kenya,
Malawi, Tanzania, Zambia, Zimbabwe); hilly, deciduous wood-
lands, 300–1400 m.
Included species (2). – E. espinosa Pax and E. guerichi-
ana Pax.
Discussion. – There are several other sections that resem-
ble sect. Espinosae in their shrubby habit, coppery bark, and
sometimes spinose branches. These include E. sect. Somalica
S. Carter, E. sect. Lyciopsis Boiss., the E. balsamifera group
(all in subg. Rhizanthium, also from Africa); and E. sect. Pla-
gianthae (subg. Chamaesyce, from Madagascar).
2. Euphorbia sect. Articulofruticosae Bruyns in Taxon 55:
416. 2006 – Type: E. aequoris N.E. Br.
Generally dioecious, semi-woody to succulent shrubs;
branches dichotomous or opposite, usually much-branched
from the base; branches cylindrical or variously ridged, api-
ces drying spine-like in some species. Leaves opposite, small
and often scale-like, quickly deciduous leaving a calloused
scar; stipules apparently absent or glandular and conspicuous.
Cyathia or cyathial cymes terminal (sometimes appearing to
be axillary when borne on apex of short shoots); cymes branch-
ing few to many times, internodes progressively shorter above;
subcyathial bracts and dichasial bracts spathulate or similar
to the leaves, deciduous. Cyathia small, usually unisexual,
subsessile; glands 5, entire, exappendiculate; styles connate at
the base and free above, bifid at the tip. Capsules subsessile or
exserted and recurved, glabrous or pubescent. Seeds conical,
obtusely 4-angled, surface finely tuberculate, ecarunculate
(Fig. 1O).
Distribution and habitat. – Most diverse in the arid winter-
rainfall region of western South Africa and southern Namibia,
extending into southern Angola and Bot swana and east to Kwa-
Zulu-Natal, South Africa. Growing in sandy soils or on rock
outcrops, in low shrublands to deserts and consolidated dunes,
from sea level to ca. 2000 m.
Included species (18–26). – E. aequoris N.E. Br. [= E. jut-
tae sensu Bruyns], E. angrae N.E. Br., E. arceuthobioides
Boiss. [= E. tenax sensu Bruyns], E. brachiata E. Mey. ex
Boiss. [= E. rhombifolia sensu Br uyns], E. burmannii E. Mey.
ex Boiss., E. caterviflora N.E. Br. [= E. rhombifolia sensu
Br uyns], E. chersina N.E. Br. [= E. rhombifolia sensu Bruyns],
E. einensis G. Will. [= E. angrae sensu Bruyns], E. ephe-
droides E. Mey. ex Boiss., E. exilis L.C. Leach, E. gentilis
N.E. Br., E. giessii L.C. Leach, E. herrei A.C. White, R.A. Dyer
& B. Sloane, E. juttae Dinter, E. lavranii L.C. Leach, E. lum-
bricalis L.C. Leach [= E. stapelioides sensu Bruy ns], E. mundii
N.E. Br. [= E. rhombifolia sensu Bruy ns], E. muricata Thunb.,
E. negromontana N.E. Br., E. rhombifolia Boiss., E. spartaria
N.E. Br., E. spinea N.E. Br., E. stapelioides Boiss., E. suffulta
Bruyns, E. tenax Burch., E. verruculosa N.E. Br.
Discussion. – This is a very well characterized group of
pencil-stemmed succulents with greatly reduced and caducous
leaves, and they are readily distinguished by their opposite
or dichotomous branching and mostly unisexual cyathia (Fig.
1B). However, species limits in this section are unclear, and the
group is in need of a taxonomic revision. Bruyns & al. (2011)
and Br uyns (in press) recognized only 18 species in this section,
but we are tentatively including here a number of names that
are treated as synonyms in those publications. According to the
age estimates of Bruyns & al. (2011), this section diversified in
southern Africa during the past 12 Ma.
3. Euphorbia sect. Cheirolepidium Boiss. in Candolle, Prodr.
15(2): 9, 70. 1862 ≡ Euphorbia subsect. Cheirolepidium
(Boiss.) Pax & K. Hoffm. in Engler, Nat. Pflanzenfam.,
ed. 2, 19c: 213. 1931 ≡ Cystidospermum Prokh., Consp.
Syst. Tithymalus Asiae Mediae: 25. 1933 ≡ Euphorbia
subg. Cystidospermum (Prokh.) Prokh. in Komarov & al.,
Flora U.R.S.S. 14: 480. 1949 – Type: E. cheirolepis Fisch.
& C.A. Mey.
= Dematra Raf., Autik. Bot.: 96. 1840 ≡ Euphorbia sect. Dema-
tra (Raf.) Prok h. in Komarov & al., Flora U.R.S.S. 14: 476.
1949 – Type: D. sericea Raf. (= E. petiolata Bank s & Sol.).
= Euphorbia subsect. Crotonopsideae Boiss. in Candolle,
Prodr. 15(2): 101. 1862 – Type: E. petiolata Banks & Sol.
= Ctenadenia Prokh., Consp. Syst. Tithymalus Asiae Mediae:
28. 1933 – Type: C. lanata (Sieb.) Prokh. (= E. petiolata
Banks & Sol.).
Annual erect herbs, well branched. Leaves and branches
opposite at the base, alternate in the mid-section before the
termination of apical growth and switch to dichotomous
branching, with each fork subtended by dichasial bracts;
leaves linear-lanceolate to elliptic or ovate, densely villous to
subglabrous, margin distinctively spinulose-dentate; stipules
subulate. Cyathia solitary between the forks of dichotomous
branches, or few-clustered in axillary cymes; both dichasial and
subcyathial bracts leaf-like but much reduced in size; glands
4 per cyathium, with deep finger-like to linear lobes, stalked
(E. cheirolepis) or not (E. petiolata), yellow-green, sometimes
turning red with age; styles 3, free or connate at the base, tip
entire; ovary densely pubescent, 3-lobed. Capsule exserted,
pubescent. Seeds 4-angled, surface tuberculate; caruncle large
and stipitate in E. petiolata (Fig. 1M), or distinctively ligulate
with two long flaps in E. cheirolepis (Fig. 1N).
Distribution and habitat. – From northern Africa through
Central Asia; fallow fields and dry, open habitats, 500–1500 m.
Included species (2). – E. cheirolepis Fisch. & C.A. Mey.,
E. petiolata Banks & Sol.
Discussion. – These two species have been variously
treated as members of subg. Esula, and they are indeed anom-
alous geographically among the remaining groups of subg.
Chamaesyce (excluding sect. Anisophyllum). However, the
presence of stipules and the pectinate cyathial glands distin-
guish both species from members of subg. Esula. The ligulate
caruncle in E. cheirolepis is unique in Euphorbia (Fig. 1N,
Pahlevani & Akhani, 2011). However, it is caducous, and seeds
may appear to be ecarunculate on herbarium sheets.
The pectinate protrusions appear to extend directly from
the rim of the glands (Fig. 1G), unli ke the petaloid appendages
in the “petaloid appendage clade”, which appear to extend
from the involucre and emerge from below the glands (Fig.
1I, J).

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4. Euphorbia sect. Eremophyton Boiss. in Candolle, Prodr.
15(2): 9, 70. 1862 ≡ Euphorbia subg. Eremophyton (Boiss.)
L.C. Wheeler in Amer. Midland Naturalist 30: 483. 1943 ≡
Euphorbia subsect. Eueremophyton (Boiss.) Pax in Engler
& Prantl, Nat. Pflanzenfam. 3(5): 107. 1891 ≡ Euphorbia
sect. Eremophila Benth. & F. Mueller, Fl. Austral. 6: 45.
1873, nom. illeg. (Art. 52.1) – Lecto type: E. eremophila
A. Cunn. (≡ E. tannensis subsp. eremophila (A. Cunn.)
D.C. Hassall), designated by Wheeler in Amer. Midland
Naturalist 30: 483. 1943.
Annual or perennial herbs to small shrubs, glabrous to
sparsely pubescent. Stems erect, multibranched; leaves and
branches opposite at the base, alternate in the mid-section be-
fore the termination of apical growth and then switching to
dichotomous branching, with each fork subtended by dichasial
bracts. Leaves linear-lanceolate to ovate, margins serrate; stip-
ules glandular or subulate. Cyathia solitary between the forks of
dichotomous branches or few-clustered in axillary cymes, with
dichasial and subcyathial bracts leaf-like but much reduced in
size; glands 4, yellow, ovate, margins entire (exappendiculate)
or crenate to palmatifid, ovary glabrous; styles 3, connate at
the base, bifid at the tips. Capsules exserted, erect, 3-lobed.
Seeds more or less 4-angled, surface tuberculate to reticulate;
caruncle present, variously shaped.
Distribution and habitat. – Australia, New Caledonia,
Vanuatu; coastal sands to inland desert and scrub, sea level
to 600 m.
Included species (3). – E. parvicaruncula D.C. Hassall,
E. planiticola D.C. Hassall, E. tannensis Spreng.
Discussion. – Boissier (1862) first established sect.
Eremophyton to include three Old World species, but they
now belong to three different sections in subg. Chamaescyce.
Besides the lectotype of this section, E. eremophila A. Cunn.,
the African E. agowensis is placed by our analyses in se ct. Sca-
torhizae, while the third species, the South African E. gueinzii,
is placed in sect. Gueinziae. Wheeler (1943) broadened the
concept of sect. Eremophyton and elevated it to the rank of
subgenus, but this was a very heterogeneous assemblage of
species that is not supported by molecular data.
Hassall (1977) treated five native Australian Euphorbia
species as forming a natural group within Euphorbia subg.
Eremophyton. However, our molecular data strongly reject the
monophyly of all five species: E. stevenii and E. boophthona
are both nested in E. subg. Euphorbia (Dorsey & al., subm.),
whereas the other three form a monophyletic group in subg.
Chamaesyce, as treated here in a more restricted sect. Ere-
mophyton. The placement of E. boophthona in subg. Chamae-
syce by Zimmermann & al. (2010) was most likely an error.
5. Euphorbia sect. Scatorhizae Y. Yang & P.E. Berry, sect.
nov. – Type: E. scatorhiza S. Carter.
Annual or perennial herbs, or shrubs; when woody often
with peeling bark; with or without tubers. Leaves alternate
basally, opposite distally, petiolate, margin entire or undulate,
sometimes with gland-tipped marginal teeth at the base; stip-
ules glandular or subulate. Cymes in 2–3-branched umbels or
cyathia solitary; subcyathial bracts small to well-developed.
Cyathia sessile or subsessile, glands 4 or 5, elliptic to subcircu-
lar, exappendiculate; styles connate at the base, bifid at the tip.
Ovary and capsule sessile or exserted on a recurved pedicel,
3-lobed, glabrous or pubescent. Seeds ovoid to oblong, more
or less 4-angled in cross-section, dorsal-ventrally f lattened,
face smooth, wrinkled, or tuberculate; ecarunculate (E. kab-
ridarensis) or with a large cap-like caruncle (E. applanata,
E. agowensis, E. polyantha, E. scatorhiza, E. trichiocyma).
Distribution and habitat. – Africa (Angola, Ethiopia,
Kenya, Somalia, Tanzania), Arabia (Saudi Arabia, Yemen),
India; rocky or sandy scrub or deserts, 200–1850 m.
Included species (7). – E. agowensis Hochst. ex Boiss.,
E. kabridarensis Thulin, E. polyantha Pax, E. scatorhiza
S. Carter, E. trichiocyma S. Ca rter. Species that may also belong
here: E. applanata Thulin & Gifri, E. suborbicularis Thulin.
Discussion. – Section Scatorhizae is characterized by
non-succulent herbs to shrubs, sessile or subsessile cyathia,
and f lattened, 4-angled seeds. All five carunculate members
have been treated in Euphorbia subg. Eremophyton (Boiss.)
L.C. Wheeler (Carter & Radcliffe-Smith, 1988; Thulin & Al-
Gifri, 1995), while the ecarunculate E. kabridarensis has been
treated in sect. Lyciopsis Boiss. (Carter, 1992).
6. Euphorbia sect. Denisiae T. Haevermans & X. Aubriot,
sect. nov. – Type: E. denisii Oudejans.
Nonsucculent, low, densely branched dwarf shrubs to small
trees, with rhizomes. Branches numerous, alternate, brownish
green with transverse linear darker patches, twigs slightly suc-
culent to ligneous. Leaves arranged spirally on short shoots,
deciduous; blade obcordate to rounded, subpeltate with a cylin-
drical petiole, margin entire; stipules small, deciduous. Cyathia
subsessile, bisexual, subterminal, subcyathial bracts present
but extremely reduced, pubescent; glands 5, yellow-green,
broadly ovate (E. denisii ) or erect with the upper margin re-
clined (E. subpeltatophylla), exappendiculate; styles connate at
base, bifid at the tip; ovary and capsule subsessile, erect, emerg-
ing from the cyathium at maturity; 3-lobed, surface smooth
and glabrous. Seeds ovoid, more or less 4-angled, apex acute,
surface smooth, with a small, reniform caruncle.
Distribution and habitat. – Southern Madagascar, in xero-
phytic vegetation, sea level to 200 m.
Included species (2). – E. denisii Oudejans, E. subpel-
tatophylla Rauh.
Discussion. – Species from southern Madagascar in the
E. tetraptera clade of subg. Euphorbia superficially resemble
E. denisii and have been incorrectly identified as this species
(Haevermans, 2003: 137, 166).
7. Euphorbia sect. Bosseriae T. Haevermans & X. Aubriot,
sect. nov. – Type: E. bosseri Leandri.
Perennial, creeping to sprawling herbs, stems succulent,
with purplish dark blotches; branching monochasial or dicha-
sial. Leaves nonsucculent, rounded and petiolate, or reduced
to scales, alternate to subopposite; stipules glandular. Cyathia
bisexual, solitary, terminal, pubescent, subcyathial bracts ap-
parently lacking; glands 4 or 5, yellow-green to brown, el-
liptic to ovate, margin entire, exappendiculate; ovary sparsely

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pubescent, subsessile and included in the cyathium cup at ma-
turity (E. bosseri, E. platyclada) or exserted on a recurved
pedicel, impairing the development of the covered gland (E. be-
marahaensis); styles 3, connate at the base, bifid almost to the
base. Capsule 3-lobed, subsessile, sparsely pubescent, surface
smooth. Seeds tuberculate and pointed in E. platyclada ; un-
known in the other two species; caruncle unknown in all three
species.
Distribution and habitat. – Southwestern and southern
Madagascar, in xerophytic vegetation, ca. 50–500 m.
Included species (3). – E. bemarahaensis Rauh & R. Man-
gelsdorff, E. bosseri Leandri, E. platyclada Rauh.
Discussion. – These three species grow in remote areas of
Madagascar and are locally rare endemics. Rauh & Mangels-
dorff (1999) placed these three species in their informal “groupe
d’E. bosseri ” but without a clear idea of its affinities. Cremers
(1984) believed E. bosseri and E. platyclada were related to
taxa like E. enterophora subsp. enterophora (subg. Euphorbia
sect. Tirucalli ), due to the presence of flattened twigs in both.
However, this relationship is not supported by our molecular
evidence.
8. Euphorbia sect. Plagianthae T. Haevermans & X. Aubriot,
sect. nov. – Type: E. plagiantha Drake.
Broom-like dioecious shrubs or trees with coppery-shiny
bark peeling in papyraceous rings. Branches alternate, densely
aggregated. Leaves scale-like and quickly deciduous (E. pla-
giantha) or developed and elongate (E. salota), distributed
all along the twigs; stipules minute. Pistillate cyathia usually
single, staminate cyathia in few-flowered cymes, on axillary
branches (reduced in E. plagiantha, elongated in E. salota);
subcyathial bracts green, inconspicuous in E. plagiantha, leaf-
like in E. salota; involucre rounded, with a sunken rim and
(4–)5(–6) inconspicuous glands with an entire margin, exap-
pendiculate; ovary glabrous; styles connate at the base, bifid
at the tip. Capsules 3-lobed, smooth and glabrous, oriented
upward; surface smooth, green. Seeds ovoid, apex pointed,
surface smooth, ecarunculate.
Distribution and habitat. – Southern Madagascar, in xero-
phytic and semi-xerophytic vegetation; sea level to 1000 m.
Included species (2). – E. plagiantha Drake, E. salota
Leandri.
Discussion. – Euphorbia plagiantha is a striking tree with
coppery, peeling bark and leafless, photosynthetic stems (Fig.
1A), whereas E. salota is a broom-like shrub. Euphorbia pla-
giantha is widely distributed in semi-xerophytic forests and
shrublands, whereas E. salota is restricted to a few ridges
around Betroka, northwest of Fort Dauphin. Both species share
the features of peeling bark, dioecy, and capsules oriented up-
wards regardless of twig orientation. They also have cyathia
with a shrunken rim bearing tiny reduced glands, and the cy-
athia are borne laterally on the distal part of the twigs, while
the vegetative branching occurs on the basal part of the twigs.
Euphorbia plagiantha, the only Madagascan species featuring
2n = 14 chromosomes (Schill, 1971), was previously grouped
with E. tirucalli (Cremers, 1984), but E. tirucalli belongs to
subg. Euphorbia (Bruyns & al., 2006).
9. Euphorbia sect. Frondosae Bruyns in Taxon 55: 416. 2006
– Type: E. goetzei Pax.
Annual or perennial herbs, or shrubs, tuberous in perennial
species. Stems terete and semi-succulent to succulent, green
and photosynthetic. Leaves alternate at base, opposite above,
glabrous or pubescent, deciduous, margin entire; stipules glan-
dular, mainly on young growth (or absent). Synflorescence of
3–5-branched terminal umbels of cymes with internodes on
primary rays up to 6–12 cm long, bracts similar to leaves in
size and shape; cyathial glands 4(5), usually bilobed (sometimes
entire), or with 2–4 suberect linear processes (E. barbicollis,
E. goetzei ); ovary glabrous or pubescent; styles free or connate
at the base, bifid up to half their length. Capsules exserted on a
reflexed pedicel; 3-lobed. Seeds ovoid to oblong, apex pointed,
4-angled in cross-section; surface wrinkled to tuberculate, with
or without a caruncle; caruncle shape and size varies.
Distribution and habitat. – Eastern to southern Africa
(Angola, Botswana, Ethiopia, Kenya, Malawi, Mozambique,
Namibia, South Africa, Tanzania, Uganda, Zambia, Zimbabwe)
and the Arabian Peninsula (Oman, Saudi Arabia, Yemen); open
to dense bushland, forest, 400–2700 m.
Included species (7). – E. barbicollis P.R.O. Bally, E. eng-
leri Pax, E. goetzei Pax, E. leistneri R.H. Archer, E. pirottae
N. Terrac., E. quaitensis S. Carter, E. transvaalensis Schltr.
Discussion. – This group is characterized by being fleshy,
stem photosynthetic herbs and shrubs. The umbellate rays are
well-spaced with long internodes. Other species that might
belong in this section include E. dolichoceras S. Carter and
E. ruficeps S. Carter. Both have ecarunculate, tuberculate seeds
and different kinds of cyathial gland appendages, but their
placements need to be further investigated.
10. Euphorbia sect. Ten ella e Pax & K. Hoffm. in Engler,
Veg. Erde 9, [Pflanzenw. Afrikas] 3, 2: 147. 1921 – Type:
E. glaucella Pax (= E. glanduligera Pax).
= Euphorbia subsect. Capensis Boiss. in Candolle, Prodr.
15(2): 66. 1862 – Type: E. phylloclada Boiss.
Annual or perennial herbs, stems decumbent or erect,
branches few to many. Leaves all opposite, narrow to subcor-
date, glabrous, margin entire or denticulate; stipules subulate
or inconspicuous. Cymes forking many times, bracts leaf-like.
Cyathial glands 4, with petaloid appendages or exappendic-
ulate (they may have a very thin rim on the glands); ovary
glabrous or pubescent; styles free or connate at the base, tip
bifid, 3-lobed. Capsule exserted on a recurved pedicel. Seeds
oblong, 4-angled in cross-section, tuberculate to smooth, with
a cap-like caruncle.
Distribution and habitat. – Southern Africa (Angola,
Botswana, Namibia, South Africa, Zimbabwe); in open desert
areas, exposed gravelly or sandy soils and rocky slopes, ca.
100 –1100 m.
Included species (4). – E. claytonioides Pax, E. glanduligera
Pax (incl. E. pfeilii Pax), E. macra Hiern., E. phylloclada Boiss.
Discussion. – This is a small, but very significant section
because it is sister to the rest of the mostly New World petaloid
appendage clade. Pax (1921: 147) recognized its similarities to
sect. Anisophyllum, and Koutnik (1984) placed E. glanduligera

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in Chamaesyce S.F. Gray (= sect. Anisophyllum) and also won-
dered whether E. pfeilii should belong here as well. Euphorbia
pfeilii was treated as distinct from E. glanduligera by Ca rter &
Leach (2001), but examination of a range of specimens shows
that they are all part of a single, distinctive species. We there-
fore include it under E. glanduligera. Apart from its extremely
slender leaves, E. macra is similar to E. glanduligera, but it has
a woody, perennial base.
Boissier (1862) placed E. phylloclada in E. [subg. Euphor-
bia] sect. Stachydium, presumably because the subcyathial
bracts are so congested, but in sect. Stachydium the plants
tend to be monochasial and the leaves enclose the cyathia more
completely than in E. phylloclada. Later, Pax (1921) placed
E. phylloclada in E. sect. Pseudacalypha Boiss., presumably
because of its axillary cyathia and herbaceous habit, but the
rest of sect. Pseudacalypha is now placed in subg. Rhizanthium
(Steinmann & Porter, 2002; Horn & al., 2012a). Euphorbia
claytonioides has subcordate leaves similar to E. phylloclada,
but its cyathial features and the glands in the leaf axils closely
resemble those of E. glanduligera. Euphorbia macra appears
to be the only perennial species in this group.
11. Euphorbia sect. Gueinziae Riina, sect. nov. – Type:
E. gueinzii Boiss.
Geophyte with tuberous roots and deciduous leaves, gla-
brous to densely pubescent; stems simple or multiple, branching
dichotomously. Leaves usually alternate on lower portion of
stem, opposite at the bifurcations of the upper branches, sub-
sessile, lanceolate to ovate-lanceolate; stipules inconspicuous,
glanduliform. Cyathia bisexual, sometimes unisexual, in termi-
nal cymes or solitary at the bifurcation of branches; glands 5,
trapezoidal or oblong-ovate, the margin entire to crenulate,
without petaloid appendages; ovar y usually pubescent; styles 3,
connate at the base, tips bifid and spreading. Capsule exserted,
subglobose, 3-lobed. Seeds oblongoid, more or less 4-angled,
obscurely sculptured, pale grayish, ecarunculate.
Distribution and habitat. – South Africa (Mpumalanga,
Free State, KwaZulu-Natal, Eastern Cape), Lesotho, and Swa-
ziland; grasslands on rocky slopes and above sandstone cliffs,
200–2000 m.
Included species (1). – E. gueinzii Boiss.
Discussion. – In his treatment of E. gueinzii in Flora
Capensis, Brown & al. (1915) characterized this species as
dioecious; however, Hargreaves (1992) contended that it is
monoecious, sometimes presenting unisexual cyathia as well
as bisexual ones. The molecular data indicate that E. gueinzii is
related to the Brazilian E. sect. Crossadenia (Figs. 2, 3), which
is consistent with its cyathial morphology and five glands, al-
though E. gueinzii is quite distinct in its geophytic habit and
inconspicuous cyathial glands. In the Euphorbia Seed Atlas
(Morawetz & al., 2010), the seed shown of E. gueinzii was
misidentified, and likely belongs to subg. Rhizanthium.
12. Euphorbia sect. Crossadenia Boiss. in Candolle, Prodr.
15(2): 9, 64. 1862 – Lectotype: E. sarcodes Boiss., desig-
nated by Wheeler in Amer. Midland Naturalist 30: 481. 1943.
= Euphorbia sect. Ephedropeplus Müll. Arg. in Martius, Fl.
Bras. 11(2):
668. 1874 ≡ Euphorbia subsect. Ephedropeplus
(Müll. Arg.) Müll. Arg. ex Pax in Engler & Prantl, Nat.
Pf lanzenfam. 3(5): 106. 1891 – Ty pe: E. gymnoclada Boiss.
Perennial herbs, small leafy shrubs, or pencil-stem shrubs,
glabrous or pubescent, stems branching dichotomously or ver-
ticellately. Leaves opposite to alternate (spiral) on the lower
stem, whorled at the base of umbellate rays, and opposite
above, either rudimentary, minute, and soon deciduous, or
well developed and persistent; stipules inconspicuous, glandu-
liform, rarely subulate. Cyathia terminal and axillary, arranged
in short cymes or umbellate cymose rays, subtended by a pair
of scale-like or foliose dichasial bracts. Involucres unisexual
or bisexual, with 4 or 5 yellowish to green, appendiculate or
exappendiculate glands; when present, gland appendages are
short crenulate-dentate or long deeply cleft to fimbriate; ovary
glabrous or pubescent; styles 3, basally connate, tips entire or
bifid. Capsule well-exserted, subglobose to deeply 3-lobed.
Seeds subglobose to ovoid, more or less 4-angled, apex mucro-
nate, surface shallowly to obscurely tuberculate, rarely smooth,
tubercles usually rounded (Fig. 1P), covered by a crustaceous,
hydrophylic layer, ecarunculate.
Discussion. – The characteristic ornamentation of the seed
coat, with low and rounded tubercles, may be a synapomor-
phy for this group. Boissier (1862) described the seeds of sect.
Crossadenia as having a crustaceous caruncle, but our obser-
vations indicate that the apical part of the seed does not have
a true caruncle; rather, the mucronate apex is an extension of
the seed coat. The whitish layer on the outside of the seeds is
hydrophilic and becomes mucilaginous when wet, much like
seeds in sect. Anisophyllum. Both molecular data (Figs. 2 &
3) and morphological characters support the division of this
group into two subsections.
Key to the subsections of E. sect. Crossadenia
1 Involucral glands 5, lacking appendages or with crenulate
to dentate appendages < 0.2 mm long .....................
..................................12a. subsect. Apparicianae
1 Involucral glands 4 (5 in E. gymnoclada), with multiple
finger-like appendages 2–4 mm long .....................
....................................... 12b. subsect. Sarcodes
12a. Euphorbia subsect. Apparicianae Riina, subsect. nov. –
Type: E. appariciana Rizzini.
Stem leaves rudimentary and soon deciduous. Involucral
glands 5, gland appendages crenate to dentate, teeth < 0.2 mm
long, or appendages lacking (E. flaviana).
Distribution and habitat. – Endemic to the state of Bahia,
Brazil, growing on granitic domes (inselbergs) or sandstone
outcrops, 250–1200 m.
Included species (3). – E. appariciana Rizzini, E. flaviana
Carn.-Torres & Cordeiro (Carneiro-Torres & al., 2012), E. teres
M. Machado & Hofacker.
12b. Euphorbia subsect. Sarcodes Riina, subsect. nov. – Type:
E. sarcodes Boiss.
Stem leaves usually well developed and persistent (rudi-

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mentary and deciduous in E. gymnoclada). Involucral glands 4
(5 in E. gymnoclada) with white, finger-like appendages, teeth
2–4 mm long.
Distribution and habitat. – Endemic to eastern-central
Brazil (Bahia, Goiás, Minas Gerais, Distrito Federal, Pernam-
buco, Piauí), in “campo rupestre” vegetation on sandy sub-
strates and coastal “restinga”, sea level to 1400 m.
Included species (6). – E. crossadenia Pax & K. Hoffm.,
E. goyazensis Boiss., E. gymnoclada Boiss., E. lycioides
Boiss., E. sarcodes Boiss., E. sessilifolia Klotzsch ex Boiss.
13. Euphorbia sect. Anisophyllum Roep. in Duby, Bot. Gall.,
ed. 2, 1: 412. 1828 ≡ Anisophyllum Haw., Syn. Pl. Succ.:
159. 1812, nom. illeg., non Jacq. 1763 ≡ Chamaesyce
Gray, Nat. Arr. Brit. Pl. 2: 260. 1821 ≡ Euphorbia subg.
Chamaesyce (Gray) Caesalp. ex. Rchb., Deut. Bot. Herb.-
Buch.: 193. 1841, nom. illeg., non Raf. 1817 – Lectotype:
Euphorbia peplis L. (≡ Anisophyllum peplis (L.) Haw. ≡
Chamaescye maritima Gray, nom. illeg., Art. 52.1) desig-
nated by Wheeler in Rhodora 43: 111. 1941.
= Aplarina Raf., New Fl. 4: 99. 1838 – Lectotype: A. prostrata
Raf. (= E. prostrata Aiton), designated by Wheeler in Rho-
dora 43: 111. 1941.
= Ditritra Raf., Sylva Tellur.: 115. 1838 – Lectotype: D. hirta
(L.) Raf. (≡ E. hirta L.), designated by Wheeler in Amer.
Midland Naturalist 30: 464. 1943.
= Endoisila Raf., Sylva Tellur.: 114. 1838 – Type: Endoisila
myrsinites Raf. (= E. myrtillifolia L.). See Wheeler (in
Amer. Midland Naturalist 30: 465. 1943) for explanation
of Rafinesque’s confusion over the specific epithet of the
type species.
= Xamesike Raf., Fl. Tellur. 4: 115. 1838 – Lectotype: X. vul-
garis Raf. (= E. chamaesyce L.), designated by Wheeler
in Amer. Midland Naturalist 30: 476. 1943.
Annual or perennial herbs, rarely subshrubs to shrubs.
Branches many, dichotomous, prostrate or ascending, rarely
erect; main shoot aborts above the cotyledon node (less often
continues growing for a few more nodes) and lateral shoots
branch dichotomously. Leaves opposite, glabrous or pubescent,
base often asymmetrical; sometimes dark green veins are visible
on leaf blades; margins entire or serrate; stipules interpetiolar,
glandular, linear, or subulate to triangular. Cyathia solitary
at the bifurcation of branches or clustered in axillary cymes;
glands 4, rarely 5–7; appendages present or absent, petaloid
when present; styles 3, free or connate at the base, tip bifid,
rarely entire; ovary and capsule glabrous or pubescent. Seed sur-
face with transverse ridges, smooth, or with irregular wrinkles;
4-angled (rarely 3-angled or rounded), ecarunculate. C, C or
C photosynthesis.
Distribution and habitat. – Warm, arid and semi-arid veg-
etation or disturbed habitats, and summer annuals of temperate
areas; nearly worldwide, sea level to 4000 m.
Discussion. – Section Anisophyllum is characterized by
its specialized growth form with early abortion of the main
shoot and with the lateral shoots producing exclusively opposite
leaves. All but three species in the section have C

photosyn-
thesis.
Key to the subsections of E. sect. Anisophyllum
1 Stipules glandular; leaf cross-section without typical
Kranz anatomy; cyathial gland appendages crenate and
fan-shaped; Texas, New Mexico, and northern Mexico .
..........................................13a. subsect. Acutae
1 Stipules subulate, triangular or ciliate, non-glandular; leaf
cross-section with Kranz anatomy; cyathial gland append-
ages absent or present (varioulsy shaped); widespread dis-
tribution ...................... 13b. subsect. Hypericifoliae
13a. Euphorbia subsect. Acutae Boiss. in Candolle, Prodr.
15(2): 18. 1862 – Type: E. acuta Engelm.
Perennial, pubescent herbs with a thickened woody taproot.
Stems prostrate, arching, ascending to erect. Leaves opposite, or
occasionally annual shoots terminate with a whorl in E. angusta ;
margin entire; stipules glandular. Cyathia solitary at the bifurca-
tion of branches; glands 4, appendages fan-shaped, equ al in size;
ovary and capsule pubescent, 3-lobed; styles bifid. Seeds ovoid,
4-angled; face smooth, with irregular shallow depressions, or
obscurely transversely rugose. C

or C

photosynthesis.
Distribution and habitat. − U.S.A. (western Texas) and
Mexico (Coahuila, Durango, Tamaulipas); grassland to desert
scrub in and around the Chihuahuan Desert on sandy or grav-
elly limestone substrates, 200–1500 m.
Included species (3). − E. acuta Engelm., E. angusta
Engelm., E. johnstonii Mayfield.
Discussion. – Subsection Acutae is diagnosed within the
section by having glandular stipules and lacking C

photosyn-
thesis.
13b. Euphorbia subsect. Hypericifoliae Boiss. in Candolle,
Prodr. 15(2): 20. 1862 – Type: E. hypericifolia L.
= Euphorbia subsect. Chamaesyce Boiss. in Candolle, Prodr.
15(2): 27. 1862, nom. illeg. per ICBN Art. 53.4 – Type:
E. chamaesyce L.
= Euphorbia subsect. Cheloneae Boiss. in Candolle, Prodr.
15(2): 16. 1862 – Lectotype: E. nummularia Hook. f., des-
ignated by Wheeler in Rhodora 43: 111. 1941.
= Euphorbia subsect. Elegantes Boiss. in Candolle, Prodr.
15(2): 18. 1862 – Type: E. elegans Spreng.
= Euphorbia subsect. Gymnadeniae Boiss. in Candolle, Prodr.
15(2): 11. 1862 ≡ Chamaesyce subsect. Gymnadeniae
(Boiss.) Koutnik in Allertonia 4: 338. 1987 – Lectotype:
E. clusiifolia Hook. & Arn., designated by Wheeler in
Amer. Midland Naturlist 30: 480. 1943.
= Euphorbia subsect. Pleiadeniae Boiss. in Candolle, Prodr.
15(2): 50. 1862 – Lectot ype: E. selloi (Klotzsch & Garcke)
Boiss., designated by Wheeler in Amer. Midland Naturalist
30: 480. 1943.
= Euphorbia subsect. Sclerophyllae Boiss. in Candolle, Prodr.
15(2): 12. 1862 ≡ Euphorbia sect. Sclerophyllae (B ois s.)
Binojk. & N.P. Balakr., Genus Euphorbia India: 201. 2010
≡ Chamaesyce G ray sect. Sclerophyllae (Boiss.) Hurusawa
in J. Fac. Sci. Univ. Tokyo, Sect. 3, Bot. 6: 275. 1954 – Lec-
totype: E. atoto G. Forst., designated by Wheeler in Amer.
Midland Naturalist 30: 480. 1943.

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= Euphorbia sect. Longistylae Binojk. & N.P. Balakr., Genus
Euphorbia India: 178. 2010 – Type: E. longistyla Boiss.
Annual or perennial herbs, rarely subshrubs to shrubs.
Branches many, dichotomous, prostrate or ascending, rarely
erect; main shoot aborts above the cotyledon node (less of-
ten continues elongation) and lateral shoots branch dichoto-
mously. Leaves opposite, glabrous or pubescent, base often
asymmetrical; sometimes dark green veins are visible on leaf
blades (Kranz anatomy); margins entire or serrate; stipules
interpetiolar, linear, subulate to triangular. Cyathia solitary
at the bifurcation of branches, or clustered in axillary cymes;
glands 4, rarely 5–7; appendages present or absent, petaloid
when present, equal or unequal in size; styles 3, free or connate
at the base, tip bifid, rarely entire; ovary and capsule glabrous
or pubescent. Seed surface with transverse ridges, smooth, or
with ir regular wrin kles; 4-angled (rarely 3-angled or rou nded).
C

photosynthesis.
Distribution and habitat. − Warm, arid and semi-arid veg-
etation or disturbed habitats, and summer annuals in temperate
areas; worldwide, from sea level to 4000 m.
Included species (365). – E. abdita (D.G. Burch) Radcl.-
Sm., E. abdulghafooriana Abedin, E. abramsiana L.C.
Wheeler, E. adenoptera Bertol., E. alainii Oudejans, E. alato-
caulis V.W. Steinm. & Felger, E. albomarginata Torr. &
A. Gray, E. allocarpa S. Carter, E. alsiniflora Baill., E. al-
sinifolia Boiss., E. amandi Oudejans, E. amplexicaulis Hoo k . f. ,
E. anisopetala (Prokh.) Prokh., E. anthonyi Brandegee,
E. anychioides Boiss., E. apatzingana McVau gh, E. apicata
L.C. Wheeler, E. arabica Hochst. & Steud. ex Anderson,
E. arabicoides N.E. Br., E. arenarioides Gagnep., E. argillosa
Chodat & Hassl., E. arizonica Engelm., E. armstrongiana
Boiss., E. arnottiana Endl., E. articulata Aubl., E. astyla En-
gelm. ex Boiss., E. atoto G. Forst., E. atrococca A. Heller,
E. australis Boiss., E. austro occidentalis Thell., E. bahiensis
(Klotzsch & Garcke) Boiss., E. balakrishnanii Binojk. & Go-
palan, E. bartolomaei Greene, E. baueri Engelm. ex Boiss.,
E. berteroana Balb. ex Spreng., E. besseri (Klot zsch & Ga rcke)
Boiss., E. biconvexa Domin, E. bifida Hook. & Arn., E. bind-
loensis (Stewart) Y. Yang, E. blodgettii Engelm. ex Hitchc.,
E. boliviana Rusby, E. bombensis Jacq., E. bracteolaris Boiss.,
E. brandegeei Millsp., E. bruntii (Proctor) Oudejans,
E. burchellii Müll. Arg., E. burmanica Hook. f., E. calderoniae
V.W. Steinm., E. camagueyensis (Millsp.) Urb., E. capillaries
Gagnep., E. capitellata Engelm., E. carissoides F.M. Bailey,
E. carunculata Waterf., E. catamarcensis (Croizat) Subils,
E. cayensis Millsp., E. celastroides Boiss., E. centralis
B.G. Thomson, E. centunculoides Kunth, E. chaetocalyx
(Boiss.) Tidestr., E. chamaerrhodos Boiss., E. chamaesyce L.,
E. chamaesycoides B. Nord., E. chamberlinii I.M. Johnst.,
E. chamissonis (Klotzsch & Garcke) Boiss., E. cinerascens
Engelm., E. clarkeana Hook. f., E. clavidigitata Gage, E. clu-
siifolia Hook. & Arn., E. coccinea B. Heyne ex Roth, E. cogh-
lanii F.M. Bailey, E. compressa Boiss., E. concanensis
M.K. Janarth. & S.R. Yadav, E. conferta (Small) B.E. Sm.,
E. convolvuloides Hochst. ex Benth., E. cordifolia Elliott,
E. corrigioloides Boiss., E. cowellii (Millsp. ex Britton) Oude-
jans, E. cozumelensis Millsp., E. crassinodis Urb., E. crepitata
L.C. Wheeler, E. crepuscula (L.C. Wheeler) V.W. Steinm. &
Felger, E. cristata B. Heyne ex Roth, E. cumbrae Boiss., E. cu-
mulicola (Small) Oudejans, E . dallachyana Baill., E. decca-
nensis V.S. Raju, E. degeneri Sherff, E. delicatissima S. Car ter,
E. deltoidea Engelm. ex Chapm., E. densiflora (Klotzsch and
Garcke) Klotzsch, E. dentosa I.M. Johnst., E. deppeana Boiss.,
E. derickii V.W. Steinm., E. diminuta S. Carter, E. dioeca
Kunth, E. drummondii Boiss., E. duckei (Croizat) Oudejans,
E. eichleri Müll. Arg., E. eleanoriae (D.H. Lorence &
W.L. Wagner) Govaerts, E. elegans Spreng., E. engelmannii
Boiss., E. erythroclada Boiss., E. eylesii Rendle, E. feddemae
McVaugh, E. fendleri Torr. & A. Gray, E. fischeri Pax,
E. flindersica Halford & W.K. Harris, E. f loribunda Engelm.
ex Boiss., E. florida Engelm., E. foliolosa Boiss., E. fosbergii
(J. Florence) Govaerts, E. fruticulosa Engelm. ex Boiss.,
E. galapageia B.L. Rob. & Greenm., E. garanbiensis Hayata,
E. garberi Engelm. ex Chapm., E. gaudichaudii Boiss., E. gey-
eri Engelm. & A. Gray, E. glyptosperma Engelm., E. goliana
Comm. ex Lam., E. golondrina L.C. Wheeler, E. gracillima
S. Watson, E. grammata (McVaugh) Oudejans, E. grandidieri
Baill., E. granulata Forssk., E. guanarensis Pittier, E. hajhi-
rensis Radcl.-Sm., E. halemanui Sherff, E. heleniana Thell. &
Stapf, E. helwigii Urb. & Ekman, E. hepatica Urb. & Ekman,
E. herbstii (W.L. Wagner) Oudejans, E. heyneana Spreng.,
E. hildebrandtii Baill., E. hirta L., E. hirtella Boiss., E. hispida
Boiss., E. hooveri L.C. Wheeler, E. hsinchuensis (S.C. Lin &
S.M. Chaw) C.Y. Wu & J.S. Ma, E. humbertii Denis, E. hu-
mifusa Willd., E. humistrata Engelm. ex A.Gray, E. hunzikeri
Subils, E. hypericifolia L., E. hyssopifolia L., E. inaequilatera
Sond., E. inaguaensis Oudejans, E. inappendiculata Domin,
E. incerta Brandegee, E. indica Lam., E. indivisa (Engelm.)
Tidestr., E. infernidialis V.W. Steinm., Euphorbia inflexa Urb.
& Ekman, Euphorbia jaegeri V.W. Steinm. & J. André, E. jame-
sonii Boiss., E. jejuna M.C. Johnst. & Warnock, E. jodhpuren-
sis Blatt. & Hallb., E. karibensis S. Carter, E. katrajensis Gage,
E. kerstingii Pax, E. kilwana N.E. Br., E. kimberleyensis
B.G. Thomson, E. kischenensis Vierh., E. klotzschii Oudejans,
E. kuriensis Vierh., E. kuwaleana O. Deg. & Sherff, E. la-
ciniata Panigrahi, E. laredana Millsp., E. lasiocarpa Klotzsch,
E. lata Engelm., E. lawsonii Binojkumar & Dwarakan, E. lech-
eoides Millsp., E. leonardii (D.G. Burch) Radcl.-Sm., E. lep-
toclada Balf.f., E. leucantha (Klotzsch & Garcke) Boiss.,
E. leucophylla Benth., E. lineata S. Watson, E. linguiformis
McVaugh, E. lissosperma S. Carter, E. liukiuensis Hayata,
E. livida E. Mey. ex Boiss., E. loandensis N.E. Br., E. longin-
sulicola S.R. Hill, E. longistyla Boiss., E. lupatensis N.E. Br.,
E. lutulenta (Croizat) Oudejans, E. luzoniensis Mer r., E. mac-
gillivrayi Boiss., E. machrisiae Steyerm., E. maconochieana
B.G. Thomson, E. maculata L., E. magdalenae Benth.,
E. makinoi Hayata, E. marayensis Subils, E. meganaesos
Featherman, E. melanadenia Torr. & A. Gray, E. mendezii
Boiss., E. mertonii Fosberg, E. mesembryanthemifolia Jacq.,
E. meyeniana Klotzsch, E. microcephala Boiss., E. micromera
Boiss., E. minbuensis Gage, E. minutula Boiss., E. missurica
Raf., E. mitchelliana Boiss., E. mossambicensis (Klotzsch &
Garcke) Boiss., E. mossamedensis N.E. Br., E. muelleri Boiss.,
E. multiformis Gaudich. ex Hook. & Arn., E. multinodis Urb.,

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E. myrtillifolia L., E. neocaledonica Boiss., E. neopolycne-
moides Pax & K. Hoffm., E. nocens (L.C. Wheeler)
V.W. Steinm., E. nodosa Houtt., E. notoptera Boiss., E. num-
mularia Hook. f., E. nutans Lag., E. obliqua F.A. Bauer ex
Endl., E. occidentaustralica Radcl.-Sm. & Govaerts, E. ocel-
lata Durand & Hilg., E. olowaluana Sherff, E. ophiolitica
(P.I. Forst.) Y. Yang, E. ophthalmica Pers., E. oranensis
(Croizat) Subils, E. orbiculata Kunth, E. orbifolia (Alain)
Oudejans, E. origanoides L., E. oxycoccoides Boiss., E. pan-
cheri Baill., E. parciflora Urb., E. paredonensis (Mi llsp.) Oude-
jans, E. parishii Greene, E. parkeri Binojkuma r & N.P. Balakr.,
E. parryi Engelm., E. parva N.E. Br., E. parviflora L., E. pe-
diculifera Engelm., E. pellegrinii Leandri, E. peninsularis
I.M. Johnst., E. peplis L., E. perennans (Shinners) Warnock
& M.C. Johnst., E. pergamena Small, E. pergracilis P.G. Mey.,
E. perlignea McVaugh, E. peruviana L.C. Wheeler, E. petrina
S. Watson, E. picachensis Brandegee, E. pilosissima S. Carter,
E. pionosperma V.W. Steinm. & Felger, E. platysperma
Engelm. ex S. Watson, E. podadenia Boiss., E. polycarpa
Benth., E. polycnemoides Hochst. ex Boiss., E. polygonifolia
L., E. pondii Millsp., E. porteriana (Small) Oudejans, E. por-
tucasadiana (Croizat) Subils, E. potentilloides Boiss., E. po-
tosina Fernald, E. proctori (D.G. Burch) Correll, E. prostrata
Aiton, E. psammogeton P.S. Green, E. pueblensis Brandegee,
E. punctulata Andersson, E. pycnostegia Boiss., E. quitensis
Boiss., E. radioloides Boiss., E. ramosa Seaton, E. rayturneri
V.W. Steinm. & E. Jercinovic, E. reconciliationis Radcl.-Sm.,
E. recurva Hook. f., E. remyi A. Gray ex Boiss., E. reniformis
Blume, E. revoluta Engelm., E. rhytisperma (Klotzsch &
Garcke) Boiss., E. riebeckii Pax, E. rivae Pax, E. rochaensis
(Croizat) Alonso Paz & Marchesi, E. rockii C.N. Forbes, E. ro-
sea Retz., E. rubriflora N.E. Br., E. ruiziana (Klotzsch &
Garcke) Boiss., E. ruizlealii Subils, E. rutilis (Millsp.) Standl.
& Steyerm., E. sabulicola Boiss., E. sachetiana (J. Florence)
Govaerts, E. salsicola S. Carter, E. salsuginosa ( McVaug h)
Radcl.-Sm. & Govaerts, E. sanmartensis Ru sby, E. scabrifolia
Kurz, E. schizolepis F. Muell. ex Boiss., E. schlechteri Pax,
E. schultzii Benth., E. schumannii Radcl.-Sm., E. schwein-
furthii Balf.f., E. scopulorum Brandegee, E. scordiifolia Jacq.,
E. sebastinei Binojk. & N.P. Balakr., E. seleri Donn. Sm.,
E. selloi (Klotzsch & Garcke) Boiss., E. selousiana S. Carter,
E. senguptae N.P. Balakr. & Subr., E. serpens Kunth, E. ser-
pyllifolia Pers., E. serratifolia S. Carter, E. serrula Engelm.,
E. setiloba Engelm. ex Torr., E. setosa (Boiss.) Müll. Arg.,
E. sharkoensis Baill., E. simulans (L.C. Wheeler) War nock &
M.C. Johnst., E. skottsbergii Sherff, E. sparrmanii Boiss.,
E. sparsiflora A. Heller, E. spellenbergiana Mayfield &
V.W. Steinm., E. spissiflora S. Carter, E. standleyi (Mil lsp.)
Oudejans, E. stictospora Engelm., E. stoddartii Fosberg,
E. subterminalis N.E. Br., E. sumbawensis Boiss., E. taihsien-
sis (Chaw & Koutnik) Oudejans, E. taluticola Wiggins, E. ta-
manduana Boiss., E. tamaulipasana (Millsp.) Oudejans, E. tet-
tensis Klotzsch, E. theriaca L.C. Wheeler, E. thymifolia L.,
E. tinianensis Hosok., E. tomentella Engelm. ex Boiss., E. to-
mentulosa S. Watson, E. torralbasii Urb., E. trachysperma
Engelm., E. trancapatae (Croizat) J.F. Macbr., E. trialata
(Huft) V.W. Steinm., E. trichophylla Baker, E. trinervia
Schumach. & Thonn., E. tumistyla (D.G. Burch) Radcl.-Sm.,
E. turpinii Boiss., E. umbellulata Engelm. ex Boiss., E. vagi-
nulata Griseb., E. vallis-mortae (Millsp.) J.T. Howell, E. vau-
thieriana Boiss., E. velleriflora (Klotzsch & Garcke) Boiss.,
E. velligera Schauer, E. vermiculata Raf., E. vestita Boiss.,
E. vezorum Leandri, E. viatilis Ule, E. villifera Scheele,
E. viminea Hook. f., E. viridula Cordem. ex Radcl.-Sm., E. vis-
coides Boiss., E. wheeleri Baill., E. yucatanensis (Millsp.)
Standl., E. zambesiana Benth.
Discussion. – Old World species of subsect. Hypericifoliae
are relatively understudied and there may be additional species
to be descr ibed as well as others to be placed in synony my. Cur-
rently David Halford (BRI) is revising the group in Australia
and has numerous new species he plans to name and publish
as part of that revision.
The following combinations are made here to recognize
the taxa at the appropriate rank within Euphorbia:
Euphorbia bindloensis (Stewart) Y. Yang, comb. nov. ≡ Eu-
phorbia articulata var. bindloensis Stewar t in Proc. Calif.
Acad. Sci., ser. 4, 1: 91. 1911 ≡ Chamaesyce bindloensis
(Stewart) D.G. Burch in Ann. Missouri Bot. Gard. 56: 176.
1969 – Type: Ecuador. Galapagos: Bindloe Island, Stewart
1968 (holotype: GH).
Euphorbia deltoidea subsp. serpyllum (Small) Y. Yang, comb.
nov. ≡ Chamaesyce serpyllum Small, Fl. Florida Keys: 81.
1913 ≡ Chamaesyce deltoidea subsp. serpyllum (Small)
D.G. Burch in Ann. Missouri Bot. Gard. 53: 99. 1966 ≡ Eu-
phorbia deltoidea var. serpyllum (Small) Oudejans in Phy-
tologia 67: 45. 1989 – Type: U.S.A. Florida: Big Pine Key,
Monroe County, J.K. Small 3811 (holotype: NY). — This
new combination is made to be consistent in recognizing
four subspecies within the Euphorbia deltoidea complex.
Euphorbia ophiolitica (P.I. Forst.) Y. Yang, comb. nov. ≡
Chamaesyce ophiolitica P.I. Forst. in Austrobaileya 5: 711.
2000 – Type: Australia. Queensland: Port Curtis District,
P.I. Forster 15042 (holotype: BRI).
14. Euphorbia sect. Poinsettia (Graham) Baill., Étude Eu-
phorb.: 284. 1858 ≡ Poinsettia Graham in Edinburgh New
Philos. J. 20: 412. 1836 ≡ Euphorbia subg. Poinsettia (Gra-
ham) House in Bull. New York State Mus. Nat. Hist. 254:
473. 1924 – Type: Poinsettia pulcherrima (Willd.) Graham
(≡ E. pulcherrima Willd.).
= Cyathophora Raf., Fl. Tellur. 4: 117. 1838 – Type: C. hetero-
phylla (Raf.) L. (≡ E. heterophylla L.).
= Pleuradena Raf., Atlantic J. 1: 182. 1833 ≡ Euphorbia subg.
Pleuradena (Raf.) Croizat in Revista Sudamer. Bot. 6: 10.
1939 – Type: Pleuradena coccinea Raf. (= E. pulcherrima
Willd.).
Annual or perennial herbs, shrubs, or small trees, from a
taproot or tuber. Earliest developing leaves and branches op-
posite, middle to upper nodes alternate or opposite/whorled,
blades usually markedly to finely serrate, rarely entire, some-
times markedly heteromorphic; stipules minute, glanduliform,

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often inconspicuous. Cyathia few to many in usually con-
gested, terminal cymes, sometimes appearing corymbiform,
leafy bracts sometimes whitish to bright red at the base or on
the entire blade; cyathial glands 1–5(–8), slightly concave to
deeply cupped, bilabiate, or circular, appendages lacking or
present and variously shaped; styles 3, free or connate at the
base, tip entire or bifid; ovary and capsule glabrous or pubes-
cent, 3-lobed. Seeds 4-angled to rounded, sharply 4-angled to
somewhat rounded in cross-section, usually truncate apically,
variously tuberculate, with or without a caruncle.
Discussion. – Species of the first two diverging subsec-
tions (subsects. Lacerae and Erianthae) are distinct in their
large caruncles and sharply 4-angled seeds. The seeds of sub-
sect. Exstipulatae, in contrast, are similar to many of those in
subsect. Stormieae, which have a coarsely tuberculate surface,
more ovoid shape, and are either carunculate or ecarunculate.
See additional discussion in the main text for an expanded jus-
tification for the broadened circumscription of sect. Poinsettia.
Key to the subsections of E. sect. Poinsettia
1 Leaves linear, mostly entire; involucral glands densely
appressed-pubescent, with laciniate, pubescent append-
ages that arch upwards and inwards over the gland ......
..................................... 14b. subsect. Erianthae
1 Leaves linear to pandurate and usually toothed (entire in
E. colorata); involucral glands either lacking appendages
or the appendages not covering the glands .............. 2
2 Involucral glands 4, appendages either horned or petal-
oid and green with crenate margins; styles entire; seeds
sharply 4-angled, finely tuberculate, with a prominent
stipitate caruncle nearly as wide as the seed itself .......
........................................ 14a. subsect. Lacerae
2 Involucral glands 1–5(–8), lacking appendages or, if
present, then appendages whitish (green and obsolete in
E. chersonesa), petaloid and not horned; styles bifid; seeds
not sharply 4-angled, apically depressed on the ventral
side, coarsely tuberculate, either ecarunculate or with a
small caruncle much narrower than the seed ............ 3
3 Involucral glands with whitish appendages ..............
................................... 14c. subsect. Exstipulatae
3 Involucral glands without appendages (or obsolete greenish
appendages in E. chersonesa) ...14d. subsect. Stormieae
14a . Euphorbia subsect. Lacerae Y. Yang & P.E. Berry, sub-
sect. nov. – Type: Euphorbia lacera Boiss.
Annual herbs from a taproot. Leaves linear-lanceolate to
pandurate, often heteromorphic, noticeably serrate, opposite
at lowest nodes, then alternate in the mid-section, the shoot
terminating with a whorl of leaves below the fertile branches;
stipules absent or glandular. Cyathia in terminal, congested,
few-cyathiate cymes, subtended by opposite leaves; glands 4,
stipitate, laterally compressed and concave; appendages horned,
or petaloid and green with crenate margins; styles entire; ovary
and capsule oblong-ovoid. Seeds 4-angled, apically angled,
finely tuberculate, with a prominent stipitate caruncle nearly
as wide as the seed itself.
Distribution and habitat. – Central and western Mexico;
xerophytic scrub, wooded ravines, 900–2500 m.
Included species (2). – E. jaliscensis B.L. Rob. & Green m.,
E. lacera Boiss.
Discussion. – The pandurate, serrate leaves of E. jaliscen-
cis are remarkably similar to those found in E. heterophylla
or E. cyathophora, and the leaves of E. lacera are also poly-
morphic. Both species in this section have cupped, stipitate
involucral glands. In both cases, the appendages are green and
somewhat fleshy, although they are much reduced and almost
obsolete in the type of E. jaliscensis var. durangensis Millsp.
Euphorbia lacera was initially placed by Boissier (1862) in
E. sect. Zygophyllidium, together with E. exstipulata in an un-
designated subcategory of § Carunculatae Boiss. The rest of
Boissier’s section consists of § Ecarunculatae Boiss., wit h two
species that belong now to sect. Alectoroctonum, E. bilobata
and E. hexagona.
14b. Euphorbia subsect. Erianthae Y. Yang & P.E. Berr y, sub-
sect. nov. – Type: Euphorbia eriantha Benth.
Annual or short-lived, pubescent, perennial herbs from a
taproot. Branches few to many from the base. Leaves linear,
appearing entire but usually with a few inconspicuous teeth
towards the apex, opposite at basal-most node, alternate in the
mid-section; stipules incon spicuous, minute and glanduliform ,
at the base of the petiole. Cyathia in terminal, congested, few-
cyathiate cymes, subtended by opposite or ternate, leaf-like
bracts; glands (2–)4–5, protruding from the outer, upper edge
of the involucre, shallowly concave; gland appendages elongate,
laciniate, densely covered with white, appressed trichomes,
arching over and concealing the glands (Fig. 1H); styles free
at the base, apex entire, purple; ovary and capsule canescent,
obloid or ovoid. Seeds 4-angled, coarsely tuberculate, covered
with a white, crustaceous coating, with a circular caruncle
about half as wide as the seed.
Distribution and habitat. – Southeastern U.S.A. (Ari-
zona, California, New Mexico, Texas) and northern Mexico
(Baja California, Baja California Sur, Chihuahua, Coahuila,
Durango, Sonora); desert scrub and thorn scrub on rocky slopes
and along washes, sea level to 900 m.
Included species (1). – E. eriantha Benth.
Discussion. – This subsection contains a single species that
is unique because of its unusual cyathial gland appendages that
curl over the gland towards the inside of the cyathium (Fig. 1H).
14c. Euphorbia subsect. Exstipulatae Y. Yang & P.E. Berry,
subsect. nov. – Type: E. exstipulata Engelm.
Small, annual herbs from a slender taproot, with oppo-
site, arcuate branching. Leaves linear to ovate, serrate, oppo-
site throughout or with some alternate leaves in the mid-stem
section in E. bifurcata. Cyathia in terminal, congested few-
cyathiate cymes; glands 1–4(–5), oblong to circular, stipitate,
laterally compressed and concave, appendages entire, undulate,
or divided into triangular segments; styles bifid; ovary and cap-
sule glabrous or pubescent on the keels, 3-lobed. Seeds broadly
ovoid, apically depressed on the ventral side, quadrangular to
rounded in cross-section, coarsely tuberculate with 2 transverse

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ridges and a tiny, reniform caruncle (in E. exstipulata), or
warty-papillate without an evident caruncle (E. bifurcata).
Distribution and habitat. – Southwestern U.S.A. to south-
ern Mexico; desert scrub, grasslands, oak forest, riparian areas,
800–2300 m.
Included species (2). – E. bifurcata Engelm., E. exstipu-
lata Engelm.
Discussion. – Euphorbia bifurcata is very similar to many
species in subsect. Stormieae in its normally single cupulate
gland, some subcyathial bracts that are whitish at the base, and
its ecarunculate, verrucose seeds. Euphorbia exstipulata was
initially placed by Boissier (1862) in E. sect. Zygophyllidium,
together with E. lacera in a subdivision named § Carunculatae
Boiss.
14d. Euphorbia subsect. Stormieae Croizat in Revista Sud-
amer. Bot. 6: 13. 1939 – Type: Euphorbia stormiae Croizat
(≡ E. radians Benth. var. stormiae (Croizat) Rzed. &
Calderón).
Annual or perennial herbs, shrubs or small trees. Branches
opposite; leaves opposite at the epicotyledonary node, leaves
and branches often alternate in the mid-section of plant, and
then opposite or whorled in the synflorescence; leaves sub-
tending the synflorescence often brightly colored. Cyathia in
terminal, usually dense, sometimes monochasial cymes; invo-
lucral glands 1–5(–8), deeply to shallowly cupped and stalked,
exappendiculate; styles 3, free or connate at the base, bifid to
about 1/2 their length from the apex, rarely entire or with only
the very apex forked; ova ry and capsule glabrous or pubescent,
3-lobed. Seeds ovoid, quadrangular or somewhat rounded in
cross-section, usually coarsely and unevenly tuberculate, or
the tubercles disposed in one or more transverse, dorsal rows;
ecarunculate, or caruncle variously shaped.
Distribution and habitat. – Widespread in the New World,
from Canada to Argentina, but with a center of distribution in
Mexico; in a wide variety of habitats from desert scrub to moist
montane forests, sea level to 2700 m.
Included species (21). – E. chersonesa Huft, E. colorata
Engelm., E. cornastra (Dressler) Radcl.-Sm., E. cuphosperma
(Engelm.) Boiss., E. cyathophora Murray, E. davidii Subils,
E. dentata Michx., E. elliptica Lam., E. heterophylla L.,
E. hormorrhiza Radcl.-Sm., E. kurtzii Subils, E. pentadac-
tyla Griseb., E. pinetorum (Small) G.L. Webster, E. pulcher-
rima Willd., E. pumicicola Huft, E. radians Benth., E. restia-
cea Benth., E. schiedeana (Klotzsch & Garcke) Mayfield ex
C. Nelson, E. strigosa Hook. & Arn., E. tubadenia Mayfield
ex Y. Yang, E. zonosperma Müll. Arg.
Discussion. – This subsection is the most diverse in sect.
Poinsettia in terms of distribution, habit, and species number.
It includes the species that Dressler (1961) included in Poinset-
tia, and those in Euphorbia subg. Poinsettia sensu Mayfield
(1997), with the addition of E. chersonesa, which Huft (1984)
thought belonged to sect. Alectoroctonum because of its ves-
tigial involucral gland appendages and relatively flat glands.
Vestigial green gland appendages were reported in E. cher-
sonesa and E. cornastra (Huft, 1984; Mayfield, 1997), but they
are very subtle and difficult for us to see when reexamining
herbarium material of these species. Mayfield (1997) recog-
nized two groups in subg. Poinsettia, the Euphorbia dentata
alliance and “subgenus Poinsettia sens.str.” Our combined
molecular tree (Fig. 3B) indicates that the E. dentata alliance
may be monophyletic, but it is nested within the rest of the
subsection.
In addition to the species listed above, there are four other
species described but not validly published in Mayfield’s (1997)
thesis. In addition, Mayfield (1997) proposed a new name and
status for another species he recognized in subg. Poinsettia.
This name is validated below.
Euphorbia tubadenia Mayfield ex Y. Yang, nom. & stat. n ov.
≡ Euphorbia dentata var. lasiocarpa Boiss. in Candolle,
Prodr. 15(2): 72. 1862 – Type: Mexico. Nuevo León: Tan-
quesillos, Jul-Oct 1842, W.F. von Karwinski s.n. (holotype:
LE). — Since the epithet lasiocarpa is occupied in Euphor-
bia (E. lasiocarpa Klotzsch), a new name is required for
this taxon when elevated to species.
15. Euphorbia sect. Alectoroctonum (Schltdl.) Baill., Étude
Euphorb.: 284. 1858 ≡ Alectoroctonum Schltdl. in Linnaea
19: 252. 1847 – Lectotype: A. scotanum (Schltdl.) Schltdl.
(≡ E. scotanum Schltdl.), designated by Wheeler in Amer.
Midland Naturalist 30: 459. 1943.
= Agaloma Raf., Fl. Tellur. 4: 116. 1838 ≡ Euphorbia subg. Aga-
loma (Raf.) House in
Bull. New York State Mus. Nat. Hist.
254: 471. 1924 – Lectotype: E. corollata L., designated
by Rafinesque in Autik. Bot: 95. 1840.
= Tithymalopsis Klotzsch & Garcke in Monatsber. Königl.
Preuss. Akad. Wiss. Berlin 1859: 249. 1859 ≡ Euphorbia
sect. Tithymalopsis (Klotzsch & Garcke) Boiss. in Can-
dolle, Prodr. 15(2): 9, 66. 1862 – Lectotype: E. corollata L.,
designated by Small in Britton & Brown, Ill. Fl. N.U.S.,
ed. 2., 2: 469. 1913.
= Zalitea Raf., New Fl. 4: 98. 1838 – Type: Z. linearis Raf.
(= E. hexagona Nut t.).
= Euphorbia sect. Zygophyllidium Boiss. in Candolle, Prodr.
15(2): 9, 52. 1862 ≡ Zygophyllidium (Boiss.) Small in Fl.
S.E. U.S.: 714, 1334. 1903 – Lectoype: Z. hexagonum
(≡ E. hexagona Nutt.), designated by Small in Britton &
Brown, Ill. Fl. N.U.S., ed. 2., 2: 468. 1913.
Annual or perennial herbs, shrubs, rarely succulent or
small trees. Stems erect to decumbent, rarely prostrate. Leaves
and branches opposite and/or alternate before the termination
of apical growth, which usually produces a 2–8-rayed pseudo-
umbel and usually equal number of leaves (sometimes there is
no apical termination and the main shoots continue elongat-
ing), and then switching to dichotomous branching, with each
fork subtended by a pair of dichasial bracts. Leaves elliptic,
ovate, obovate to linear, margin entire, rarely crenulate; stipules
mostly minute and glandulifor m, rarely subulate-f iliform. Cy-
athia solitary or in cymes, terminal or axillary; both dichasial
and subcyathial bracts leaf-like, sometimes greatly reduced in
size, or white and showy; glands 5 per cyathium (rarely 2, 3,
4 or 6), flat or shallowly concave, appendages petaloid; styles
free at the base, tip bifid or rarely entire; ovary and capsule

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glabrous or pubescent, capsule exserted at maturity; 3-lobed.
Seeds ovoid, subglobose, or oblong, more or less 4-angled to
rounded; surface smooth or with wart-like protrusions, some-
times distinctively shallowly to deeply pitted, ecarunculate or
rarely carunculate.
Distribution and habitat. – Widespread in the New World
from Canada to Argentina, with a center of diversity in Mexico
and Central America; tropical and subtropical forests, desert
scrub, and disturbed areas, sea level to 3000 m.
Included species (115). – E. aaron-rossii A.H. Holmgren
& N.H. Holmgren, E. acerensis Boiss., E. adiantoides Lam.,
E. alata Hook., E. antisyphilitica Zucc., E. arenaria Kunth,
E. ariensis Kunth, E. armourii Millsp., E. arteagae W.R. Buck
& Huft, E. barnesii (Millsp.) Oudejans, E. bicolor Engelm. &
A. Gray, E. bilobata Engelm., E. calcicola Fernald, E. cali-
fornica Benth., E. caperata McVaug h , E. cassythoides Boiss.,
E. ceroderma I.M. Johnst., E. chenopodiifolia Boiss., E. col-
letioides Benth., E. corollata L., E. cotinifolia L., E. curti-
sii Engelm., E. cymosa Poir., E. defoliata Urb., E. delicatula
Boiss., E. dioscoreoides Boiss., E. discoidalis Chapm., E. du-
gandiana Croizat, E. dwyeri D.G. Burch, E. eglandulosa
V.W. Steinm., E. ellipsifolia Gilli, E. ephedromorpha Bartlett
ex B.L. Rob. & Bartlett, E. equisetiformis A. Stewart, E. este-
vesii N. Zimm. & P.J. Braun, E. exserta (Small) Coker, E. fran-
coana Boiss., E. fraseri Boiss., E. fulgens Karw. ex Klotzsch,
E. gentryi V.W. Steinm. & T.F. Daniel, E. gradyi V.W. Steinm.
& Ram.-Roa, E. graminea Jacq., E. guadalajarana S. Wat-
son, E. guatemalensis Standl. & Steyerm., E. guiengola
W.R. Buck & Huft, E. gumaroi J. Meyrán, E. haematantha
Boiss., E. henricksonii M.C. Johnst., E. hexagona Nutt. ex
Spreng., E. hexagonoides S. Watson, E. hindsiana Benth.,
E. hintonii L.C. Wheeler, E. humayensis Brandegee, E. in-
nocua L.C. Wheeler, E. insulana Vel l., E. ipecacuanhae L.,
E. ixtlana Huft, E. jablonskii V.W. Steinm., E. lagunensis
Huft, E. lancifolia Schltdl., E. leucocephala Lotsy, E. lottiae
V.W. Steinm., E. luciismithii B.L. Rob. & Greenm., E. mac-
ropodoides B.L. Rob. & Greenm., E. macropus (Klotzsch &
Garcke) Boiss., E. macvaughii Carvajal & Lomelí, E. mar-
ginata Pursh, E. mercurialina Michx., E. mexiae Standl.,
E. misella S. Watson, E. misera Benth., E. monantha C. Wright
ex Boiss., E. montereyana Millsp., E. multiseta Benth., E. mus-
cicola Fernald, E. nayarensis V.W. Steinm., E. nephradenia
Barneby, E. oaxacana B.L. Rob. & Greenm., E. ocymoidea
L., E. oerstediana (Klotzsch & Garcke) Boiss., E. oppositifolia
McVaugh, E. petiolaris Sims, E. poeppigii (Klot zsch & Garcke)
Boiss., E. polyphylla Engelm. ex Holz., E. pubentissima Mi-
chx., E. rossiana Pax, E. rzedowskii McVaugh, E. saccharata
Boiss., E. scandens Kunth, E. schlechtendalii Boiss., E. sciad-
ophila Boiss., E. scotanum Schltdl., E. segoviensis (Klotzsch
& Garcke) Boiss., E. sinaloensis Brandegee, E. sonorae Rose,
E. soobyi McVaugh, E. sphaerorhiza Benth., E. spruceana
Boiss., E. strictior Holz., E. subpeltata S. Watson, E. sub-
reniformis S. Watson, E. subtrifoliata Rusby, E. succedanea
L.C. Wheeler, E. surinamensis Lanj., E. tresmariae (Mill sp.)
Standl., E. tricolor Greenm., E. umbrosa Bertero ex Spreng.,
E. verapazensis Standl. & Steyerm., E. violacea Greenm.,
E. viridis (Klotzsch & Garcke) Boiss., E. whitei L.C. Wheeler,
E. wrightii Torr. & A. Gray, E. xalapensis Kunth, E. xanti
Engelm. ex Boiss., E. xbacensis Millsp., E. zierioides Boiss.
Discussion. – Section Alectoroctonum is characterized
by tiny, mostly glanduliform stipules, petaloid gland append-
ages, and usually entire leaves. Schlechtendal (1847) coined the
genus name Alectoroctonum after the Spanish common name
for “rooster killer”, presumably referring to the toxicity of the
species he assigned to the group.
Due to limited resolution in our analysis, incongruence
among markers, and frequent convergence in morpholog y, ad-
ditional markers will be required to better resolve relationships
within sect. Alectoroctonum. Therefore here we are not propos-
ing any formal subsections, but instead some of the distinct
subclades were considered in the discussions.
acknowledgeMents
The authors thank V.W. Steinmann, Y. Ramírez-Amezcua,
R. Becker, A. Moller, S. Ghazanfar, and the Missouri Botanical Garden
for faci lit ati ng field work; T.R. van Devend er, A.L. Reina-G., V.W. Stei n-
mann, P. Carrillo-Reyes, J.W. Horn, B.W. van Ee, K.J. Wurdack, and
B.L. Dorsey for providing plant samples; and curators of the follow-
ing herbaria who allowed us to sample and examine their specimens:
COLO, M, MA, MIC H, MO, and UPS. We thank S. Pereira , H. Draheim,
B.S. Wagner, D.J. Landau, and B. Oyserman for help with lab work;
V.W. Steinmann, J.A. Peirson, J.W. Horn, and B.L. Dorsey for valuable
discussion and help revising the manuscript; and P.V. Bruyns and an
anonymous reviewer for help improving the manuscript. Funding was
provided by the National Science Foundation through a Planetary Bio-
diversity Inventory award (DEB-0616533) to PEB.
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Appendix.
Specimens used in this study.
Taxon, collector, and collection number (herbarium acronym), collection locality, and GenBank accession numbers for ITS and ndhF sequences, respectively.
Sequences without collection infor mation were downloaded from GenBank.
Euphorbia aaron-rossii A.H. Holmgren & N.H. Holmgren, AF537396, –; Euphorbia acanthothamnos Heldr. & Sart. ex Boiss., Riina 1563 (MICH), Greece:
Crete, JQ750879, JQ750756; Euphorbia acerensis Boiss., Van Ee 648 (MICH, SI, US), Argentina: Córdoba, JQ750872, JQ750757; Euphorbia acuta Engelm.,
AF537450, AF538176; Euphorbia adiantoides Lam., AF537395, –; Euphorbia aequoris N.E. Br. 1, Becker 1167 (MICH, PRE, UNIN), South Africa: Western
Cape, JQ750873, JQ750758; Euphorbia aequoris N.E. Br. 2, Becker 1277 (MICH, PRE, UNIN), South Africa: Northern Cape, JQ750874, JQ750759; Euphor-
bia agowensis Hochst. ex Boiss., AF537419, –; Euphorbia alata Hook., Campbell s.n . (FTG), U.S.A.: cultivated at Fairchild Tropical Botanical Garden,
#2009-0138, originally from Jamaica: Cockpit country, JQ750875, JQ750760; Euphorbia albipollinifera L.C. Leach, Marx 209 (from the field, MA) and Riina
1611 (from living collection, MICH), Netherlands: private living collection of R. van Veldhuisen, originally from South Africa: Eastern Cape, JQ750870,
JQ750761; Euphorbia albomarginata Torr. & A. Gray, Reina-G. 20 06-389 (MICH), Mexico: Sonora, HQ645221, JQ750762; Euphorbia angusta Engelm.,
Yang 41 (MICH), U.S.A.: Texas, HQ645222, JQ750763; Euphorbia antisyphilitica Zucc., Yang 8 (MICH), U.S.A.: Texas, JQ750876, JQ750764; Euphorbia
appariciana Rizzini, Caruzo 138 (HUEFS), Brazil: Bahia, JQ750877, JQ750765; Euphorbia arceuthobioides Boiss., AM040758, –; Euphorbia arie nsis Kunth,
AF537409, –; Euphorbia arteagae W.R. Buck & Huft, Steinmann 2354 (MICH), Mexico, JQ750878, JQ750766; Euphorbia barbicollis P.R.O. Bally, Horn s.n.
(Arid Lands Nursery), U.S.A.: Cultivated at Arid Lands Nursery, Tucson, Arizona, originally from Somalia., JQ750881, JQ750767; Euphorbia beharensis
Leandri, Yang 188 (MICH), U.S.A.: Cultivated at Fairchild Tropical Botanical Garden, #2006-1173*A, originally from Madagascar, JQ750890, JQ750768;
Euphorbia bemarahaensis Rauh & R. Mangelsdorff, AJ508984, –; Euphorbia bicolor Engelm. & A. Gray, AF537386, –; Euphorbia bifurcata Engelm.,
AF537434, AF538173; Euphorbia bilobata Engelm., Van Devender 2007-1036 (MICH), Mexico: Sonora, JQ750882, JQ750769; Euphorbia brachiata (E. Mey
ex Klotzsch & Garcke) Boiss., Morawetz. 280 (MICH), South Africa: Western Cape, JQ750883, JQ750770; Euphorbia breviarticulata Pax, Morawet z 375
(EA, MICH, MO), Kenya, JQ750885, JQ750771; Euphorbia burmannii (Klotzsch & Garcke) E. Mey. ex Boiss. 1, Morawetz 266 (MICH, NBG), South Africa:
Easter n Cape, JQ750884, JQ750772; Euphorbia burmannii (Klotzsch & Garcke) E. Mey. ex Boiss. 2, Becker 873 (PRE, UNIN), South Africa: Western Cape,
JQ750933, JQ750823; Euphorbia calcicola Fernald, AF537385, –; Euphorbia californica Benth., Sanchez 06 -050 (MICH), Mexico: Sonora, JQ750892,
JQ750773; Euphorbia caperata McVau gh, Steinmann 5891 (IEB), Mexico, JQ750893, JQ750774; Euphorbia capitellata Engelm., Reina- G. 2006-539 (MICH),
Mexico: Sonora, HQ645237, JQ750775; Euphorbia cassythoides Boiss., AF537387, –; Euphorbia caterviflora N.E. Br., Becker 1126 (MICH, PRE, UNIN),
South Africa: Nor thern Cape, JQ750894, JQ750776; Euphorbia celastroides Boiss., Berry 7864 (MICH), U.S.A.: cultivated at the Huntington Botanical
Gardens, California, originally from U.S.A.: Hawaii, JQ750895, JQ750777; Euphorbia ceroderma I.M. Johnst., AF537389, AF538153; Euphorbia cheirolepis
Fisch. & C.A. Mey. ex Karelin, AF537424, –; Euphorbia chersina N.E. Br., Becker 903 (PRE, UNIN), South Africa: Norther n Cape, JQ750896, JQ750778;
Euphorbia chersonesa Huft, AF537436, AF538174; Euphorbia colletioides Benth., Reina-G. 2006-1314 (MICH), Mexico: Sonora, JQ750897, JQ750779;
Euphorbia colorata Engelm., Van Devender 2006-1031 (MICH), Mexico: Sonora, JQ750898, JQ750780; Euphorbia cornastra (Dressler) Radcl.-Sm., Berry
7840 (MICH), U.S.A.: cultivated at the Ecke Ranch, Encinitas, California, JQ750899, JQ750781; Euphorbia corollata L., Berry 7764 (MICH), U.S.A.: Indiana,
JQ750900, JQ750782; Euphorbia cotinifolia L., Riina 1587 (VEN), Venezuela: Edo. Vargas, JQ750901, JQ750783; Euphorbia crossadenia Pax & K. Hoffm.,
Giulietti 2417 (HUEFS), Brazil: Bahia, JQ750902, –; Euphorbia crotonoides subsp. crotonoides Boiss., Morawetz 456 (DSM, K, MICH, MO, NHT), Tanza-
nia: Rukwa Region, JQ750871, JQ750784; Euphorbia cuphosperma (Engelm.) Boiss., Yang 44 (MICH, IEB), Mexico: Guanajuato, JQ750903, JQ750785;
Euphorbia cyathophora Murray, Yang 129 (MICH), U.S.A.: Florida, JQ750904, JQ750786; Euphorbia cymosa Poir., Van Ee 761 (MICH), Jamaica: St. Andrew,
JQ750905, JQ750787; Euphorbia delicatula Boiss., AF537393, AF538152; Euphorbia de nisii Oudejans, Dorsey 184 (MICH, TAN, MO), Madagascar: Toliara,
–, JQ750788; Euphorbia dentata Michx., Van Ee 627 (MICH, SI, US), Argentina: Córdoba, JQ750906, JQ750789; Euphorbia dioscoreoides subsp. attenuata
V.W. Steinm., Reina-G. 2006-562 (MICH), Mexico: Sonora, JQ750907, JQ750790; Euphorbia eglandulosa V.W. Steinm., AF537394, –; Euphorbia einensis
G. Will., Becker 911 (PRE, UNIN), South Africa: Northern Cape, JQ750908, JQ750791; Euphorbia ephedroides E. Mey. ex Boiss., Becker 908 (PRE, UNIN),
South Africa: Northern Cape, JQ750909, JQ750792; Euphorbia equisetiformis A. Stewart, AF537388, –; Euphorbia eriantha Benth., AF537440, AF538167;
Euphorbia espinosa Pax, AF537416, AF538190; Euphorbia exilis L.C. Leach 1, AM040767, –; Euphorbia exilis L.C. Leach 2, Becker 894 (PRE, UNIN),
South Africa: Northern Cape, JQ750913, JQ750798; Euphorbia exstipulata Engelm., Reina-G. 2006 -674 (MICH), Mexico: Sonora, JQ750910, JQ750793;
Euphorbia flaviana Carneiro-Tor res & Cordeiro, AF537457, –; Euphorbia florida Engelm., Reina-G. 2006- 476 (MICH), Mexico: Sonora, HQ645268, JQ750794;
Euphorbia francoana Boiss., Steinmann 2083 (MICH), Mexico: Michoacan, JQ750911, JQ750795; Euphorbia fulgens Karw. ex Klotzsch, AF537404, AF538154;
Euphorbia gentilis N.E. Br., Becker 1188 (MICH, PRE, UNI N), South Africa: Western Cape, JQ750912, JQ750796; Euphorbia gentryi V.W. Steinm. & T.F.
Daniel, AF537406, –; Euphorbia giess ii L.C. Leach, Becker 1366 (WIND, MICH, PRE, UNIN), Namibia: Erongo, –, JQ750797; Euphorbia glanduligera Pax,
AF537426, AF538178; Euphorb ia goetzei Pax, AF537413, AF538185; Euphorbia goya zensis Boiss., Caruzo 139 (HUEFS), Brazil: Bahia, JQ750914, JQ750799;
Euphorbia gradyi V.W. Steinm. & Ram.-Roa, AF537407, AF538151; Euphorbia graminea Jacq. 1, Berry 7843 (MICH), U.S.A.: cultivated at the Ecke Ranch,
Encinitas, California, JQ750915, JQ750800; Euphorbia graminea Jacq. 2, Christenhusz 3297 (MICH), Jamaica, JQ750945, JQ750801; Euphorbia guadala-
jarana S. Watson, Carrillo-Reyes 5902 (IEB), Mexico: Jalisco, JQ750916, JQ750802; Euphorbia guatemalensis Standl. & Steyerm., AF537408, –; Euphorbia
gueinzii Boiss., Hobson 2141 (PRE), Swaziland, JQ750917, JQ750803; Euphorbia guerichiana Pax, Becker 929 (PRE, UNIN), South Africa: Northern Cape,
JQ750918, JQ750804; Euphorbia guiengola W.R. Buck & Huft, Berry 7753 (MICH), U.S.A.: cultivated at the green house of UC-Davis, California, #B76.047,
JQ750919, JQ750805; Euphorbia gumaroi J. Meyrán, Steinmann 5813 (MICH, IEB), Mexico: Hidalgo, JQ750920, JQ750806; Euphorbia gymnoclada Boiss.,
Caruzo 130 (HUEFS), Brazil: Bahia, JQ750921, JQ750807; Euphorbia gymnonota Boiss., Yang 185 (MICH), U.S.A.: Cultivated, JQ750886, JQ750808; Eu-
phorbia hainanensis Croizat, Gilbert 501 (MO, K), China: Hainan, JQ750922, –; Euphorbia helioscopia L., Riina 1607 (MICH), Spain: Castilla y Leon,
JQ750880, JQ750809; Euphorbia herrei A.C. White, R.A. Dyer & B. Sloane, Becker 937 (PRE, UNIN), South Africa: Nor thern Cape, JQ750923, JQ750810;
Euphorbi a heterophylla L., Riina 1596 (VEN), Venezuela: Barinas, JQ750924, JQ750811; Euphorbia hexagona Nutt. ex Spreng., Clark 1793 (COLO), U.S.A.:
Colorado, JQ750925, JQ750812; Euphorbia hindsiana Benth., Steinmann 6438 (IEB, MICH), Mexico: Baja California Sur, JQ750926, JQ750813; Euphorbia
hinkleyorum I.M. Johnst., Carrillo-Reyes 5963 (CORD), Argentina: Jujuy, JQ750887, JQ750814; Euphorbia hirta L., Reina-G. 20 06-470 (MICH), Mexico:
Sonora, HQ645278, JQ750815; Euphorbia hormorrhiza Radcl.-Sm., AF537431, AF538165; Euphorbia humayensis Brandegee, Steinmann 1153 (MICH),
Mexico: Sinaloa, JQ750927, JQ750816; Euphorbia humifusa Willd., Schuhwerk 06/511 (MICH), Ger many: Oberpfalz, JQ750928, JQ750817;

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Euphorbi a hyssopifolia L., Van Deven der 2006-463 (MICH), Mexico: Sonora, HQ645283, JQ750818; Euphorb ia innocua L.C. Whe eler, AF537380, AF538161;
Euphorbia insulana Vel l., Riina 1586 (VEN), Venezuela: Dtto. Federal, JQ750930, JQ750819; Euphorbia ipecacuanhae L., AF537397, –; Euphorbia ixtlana
Huft, Car rill o-R eye s 5555 (IEB, MICH), Mexico: Oaxaca, JQ750931, JQ750820; Euphorbia jaliscensis B.L. Rob. & Greenm., AF537442, AF538166; Euphor-
bia juttae Dinter 1, AF537418, AF538188; Euphorbia juttae Dinter 2, Becker 1402 (WIND, MICH, PRE, UNIN), Namibia: Karas, JQ750932, JQ750821;
Euphorbia kabridarensis Thulin, Thulin 11585 (UPS), Ethiopia: Somali National Regional State, –, JQ750822; Euphorbia lacera Boiss., AF537441, –;
Euphorbia lagunensis Huft, AF537379, –; Euphorbia lei stneri R.H. Archer, Morawetz 303 (MICH), South Africa, JQ750934, JQ750824; Euphorbia leuco-
cephala Lotsy, Yang 125 (MICH), U.S.A.: Florida, JQ750935, JQ750825; Euphorbia lumbricalis L.C. Leach, AM040779, –; Euphorbia lycioide s Boiss.,
Farias Castro 2030 (EAC), Brazil: Piaui, JQ750936, JQ750826; Euphorbia macropodoides B.L. Rob. & Greenm., Anderson 4840 (MICH), Mexico: Oaxaca,
JQ750937, JQ750827; Euphorbia macropus (Klotzsch & Garcke) Boiss., Van Devender 2006-1033 (MICH), Mexico: Sonora, JQ750938, JQ750828; Euphor-
bia maculata L., Schuhwerk 6/598 (M), JQ750939, JQ750829; Euphorbia mac vaughii Carvajal & Lomelí, AF537382, –; Euphorbia marginata Pur sh, AJ534787,
AJ534788, EU022037; Euphorbia mexiae Standl., Carrillo-Reyes 5800 (MICH), Mexico: Jalisco, JQ750942, JQ750831; Euphorbia misella S. Watson,
AF537384, AF538160; Euphorbia misera Benth., AF537383, EU022036; Euphorbia mundii N.E. Br., Becker 1147 (MICH, PRE, UNIN), South Africa: West-
ern Cape, JQ750943, JQ750832; Euphorbia oaxacana B.L. Rob. & Greenm., AF537373, –; Euphorbia ocymoidea L., Van Devender 2007-1346 (MICH),
Mexico, JQ750944, JQ750833; Euphorbia oerstediana Klotzsch & Garcke Boiss., –, AF538159; Euphorbia parvicaruncula D.C. Hassall, AJ534809+AJ534810,
–; Euphorbia pediculifera Engelm., Reina-G. 2006- 483 (MICH), Mexico: Sonora, JQ750946, JQ750834; Euphorbia pentadactyla Griseb., AF537428, –;
Euphorbia pervilleana Baill., Dorsey 188 (MICH, TAN, MO), Madagascar: Toliara, JQ750888, JQ750835; Euphorbia petiolata Banks & Sol., AF537422,
AF538180; Euphorbia phosphorea Mart., Caruzo 145 (HUEFS), Brazil: Bahia, JQ750889, JQ750836; Euphorbia phylloclada Boiss., AF537427, AF538179;
Euphorbia pinetorum (Small) G.L. Webster, Yang 168 (MICH), U.S.A.: Florida, JQ750947, JQ750837; Euphorbia pirottae N. Terrac., AF537417, AF538186;
Euphorbia plagiantha Drake, Dorsey 164 (MICH, TAN, MO), Madagascar: Toliara, –, JQ750838; Euphorbia planiticola D.C. Hassall, Gillespie 7324 (MICH),
Australia: New South Wales, –, JQ750839; Euphorbia platyclada Rauh, AF537421, AF538187; Euphorbia poeppigii (Klotzsch & Garcke) Boiss.,
AJ534793+AJ534794, –; Euphorbia polyantha Pax, –, EU022107; Euphorbia polygonifolia L., Berry 7765 (MICH), Canada: Ontario, JQ750948, JQ750840;
Euphorbia polyphylla Engelm. ex Holz., Yang 0158 (MICH), U.S.A.: Florida, JQ750949, JQ750841; Euphorbia pulcherrima Willd. ex Klotzsch, Van Devender
20 07-117 7 (MICH), Mexico, JQ750950, JQ750842; Euphorbia pumicicola Huft, AF537437, AF538164; Euphorbia quaitensis S. Carter, –, EU022061; Eu-
phorbia radians Benth., AF537438, AF538169; Euphorbia rhombifolia Boiss. 1, AF537414, AF538183; Euphorbia rhombifolia Boiss. 2, Becker 864 (PRE,
UNIN), South Africa: Western Cape, JQ750929, JQ750843; Euphorbia rhombifolia Boiss. 3, Becker 1105 (MICH, PRE, UNIN), South Africa: Eastern Cape,
JQ750951, JQ750844; Euphorbia rossiana Pax, AF537374, –; Euphorbia royleana Boiss., Berr y 7739 (MICH), U.S.A.: Cultivated, JQ750891, JQ750845;
Euphorbia rzedowskii McVaugh, AF537399, –; Euphorbia salota Leandri, Aubriot 28 (P, MICH), Madagascar: Androy, JQ750952, JQ750846; Euphorbia
sarcodes Boiss., Caruzo 141 (HUEFS), Brazil: Bahia, JQ750953, JQ750847; Euphorbia scandens Kunth, Carrillo-Reyes 5146 (IEB, MICH), Mexico: Chiapas,
JQ750954, JQ750848; Euphorbia scatorhiza S. Carter, AF537420, AF538181; Euphorbia schlechtendalii Boiss., Steinmann 2172 (MICH, IEB), Mexico:
Michoacan, JQ750955, JQ750849; Euphorbia sciadophila Boiss., Van Ee 650 (MICH, SI, US), Argentina: Córdoba, JQ750956, JQ750850; Euphorbia segov-
iensis (Klotzsch & Garcke) Boiss., AF537400, –; Euphorbia sessilifolia Klotzsch ex Boiss., Caruzo 133 (HUEFS), Brazil: Bahia, JQ750957, JQ750851; Eu-
phorbia setiloba Engelm. ex Torr., Reina-G. 2006-478 (MICH), Mexico: Sonora, HQ645345, JQ750852; Euphorbia setosa (Boiss.) Müll.Arg., Cordeiro 3025
(SP), Brazil: Minas Gerãis, HQ645346, JQ750853; Euphorbia sinaloensis Brandegee, AF537401, AF538156; Euphorbia sonorae Rose, Reina-G. 2006- 830
(MICH), Mexico: Sonora, JQ750958, JQ750854; Euphorbia soobyi McVau gh, Carrillo- Reyes 5895 (MICH), Mexico: Jalisco, JQ750959, JQ750855; Euphorbia
sp. nov. 1, Ramírez-Amezcua 1428 (MICH, IEB), Mexico: Michoacán, JQ750962, JQ750856; Euphorbia sp. nov. 2, Steinmann 6586 (IEB), Mexico: Michoacán,
JQ750960, JQ750857; Euphorbia sp. nov. 3, Van Devender 2006-1030 (MICH), Mexico: Sonora, JQ750961, JQ750858; Euphorbia sp. nov. 4, Linneo 1053
(MO), Bolivia: Santa Cruz, JQ750940, JQ750830; Euphorbia sp. nov. 5, Steinmann 5833 (IEB), Mexico: Querétaro, JQ750970, JQ750869; Euphorbia spartaria
N.E. Br., Becker 1370 (WIND, MICH, PRE, UNIN), Namibia: Khomas, –, JQ750859; Euphorbia sphaerorhiza Benth. 1, Yang 110 (MICH, IEB), Mexico:
Michoacán, JQ750963, JQ750860; Euphorbia sphaerorhiza Benth. 2, Breedlove 63154 (MICH), Mexico: Durango, JQ750941, JQ750861; Euphorbia spinea
N.E. Br., Becker 967 (PRE, UNIN), South Africa: Northern Cape, JQ750964, JQ750862; Euphorbia stapelioides Boiss., AM040790, –; Euphorbia strigosa
Hook. & Arn., AF537439, AF538163; Euphorbia subpeltata S. Watson, Ramírez-Amezcua 1129 (IEB), Mexico, JQ750965, JQ750863; Euphorbia subrenifor-
mis S. Watson, Van Devender 2006-1003 (MICH), Mexico: Sonora, JQ750966, JQ750864; Euphorbia succedanea L.C. Wheeler, AF537403, AF538162; Eu-
phorbia suffulta Bruyns, AM040794, –; Euphorbia tannensis subsp. tannensis Spreng., AF537425, AF538184; Euphorbia tannensis subsp. eremophila (A.
Cunn. ex Hook.) D.C. Hassall, AF537423, –; Euphorbia thymifolia L., Van Devender 20 06-628 (MICH), Mexico: Sonora, JQ750967, JQ750865; Euphorbia
tresmariae (Millsp.) Standl., Steinmann 1089 (MICH, RSA), Mexico: Jalisco, JQ750968, JQ750866; Euphorbia whitei L.C. Wheeler, AF537391, –; Euphorbia
xalapensis Kunth, Steinmann 4221 (MICH, IEB), Mexico: Michoacan, –, JQ750867; Euphorbia xanti Engelm. ex Boiss., Yang 0199 (IEB, MICH), Mexico:
Baja California Sur, JQ750969, JQ750868; Euphorbia zonosperma Müll. Arg., AF537430, –.
Appendix.
Continued.