Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus Tridimeris (Annonaceae)

Abstract

Tridimeris is the only genus of Annonaceae endemic to Mexico, and since its description more than 150 years ago, the genus has been largely ignored. Here, based on herbarium specimens and a comprehensive phylogenomic study involving hundreds of nuclear markers, the first taxonomic revision of the genus Tridimeris (Annonaceae, Malmeioideae, subtribe Sapranthinae) is presented. Ten species are recognized, six of which are newly described here. All the species are exclusively found in Mexico's most humid forests, particularly in the montane cloud forest and the tropical rainforest. The genus Tridimeris is morphologically distinguished from other neotropical genera of the Annonaceae by its leaves with pocket domatia present in the axils of the secondary veins, by its dimerous flowers (two sepals and four petals), basally fused sepals with ciliated margins, by a reduced number of carpels per flower (1–5) and by its large and fleshy fruits (monocarps) with numerous seeds. A highly resolved phylogenetic hypothesis provides strong support for the relationships among Tridimeris species, forming two well-supported clades. Consequently, two new sections are proposed, namely Tridimeris sect. Tridimeris and Tridimeris sect. Zoque. A detailed description of the morphology of the genus is presented, including the description of the pollen, domatia and its phylogenetic relationships. Taxonomic treatments of the species include synonyms, geographic and ecological notes, comparisons with similar species and a preliminary assessment of their conservation status. All species of the genus are potentially threatened with extinction and eight are assessed as Critically Endangered, which makes it the most threatened lineage of Mexican trees. This study emphasizes the importance of scientific collections as invaluable sources of data for current taxonomic revisions and conservation. It is a formal invitation to preserve and support the basic scientific research.

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Vol.:(0123456789)
Plant Systematics and Evolution (2024) 310:47
https://doi.org/10.1007/s00606-024-01929-8
RESEARCH
Taxonomy, systematics andconservation ofthehighly threatened
andendemic Mexican genus Tridimeris (Annonaceae)
AndrésErnestoOrtiz‑Rodriguez1· FrancisJ.Nge2· CarlosRodrigues‑Vaz2,3· VincentSoulé2· GeorgeE.Schatz4·
MaríaFernandaMartínez‑Velarde1· LeopoldoHurtado‑Reveles1· MoisesRangel‑Olguin1· ThomasL.P.Couvreur2
Received: 20 September 2023 / Accepted: 28 October 2024 / Published online: 2 December 2024
© The Author(s) 2024
Abstract
Tridimeris is the only genus of Annonaceae endemic to Mexico, and since its description more than 150years ago, the genus
has been largely ignored. Here, based on herbarium specimens and a comprehensive phylogenomic study involving hundreds
of nuclear markers, the first taxonomic revision of the genus Tridimeris (Annonaceae, Malmeioideae, subtribe Sapranthinae)
is presented. Ten species are recognized, six of which are newly described here. All the species are exclusively found in
Mexico's most humid forests, particularly in the montane cloud forest and the tropical rainforest. The genus Tridimeris is
morphologically distinguished from other neotropical genera of the Annonaceae by its leaves with pocket domatia present in
the axils of the secondary veins, by its dimerous flowers (two sepals and four petals), basally fused sepals with ciliated mar-
gins, by a reduced number of carpels per flower (1–5) and by its large and fleshy fruits (monocarps) with numerous seeds. A
highly resolved phylogenetic hypothesis provides strong support for the relationships among Tridimeris species, forming two
well-supported clades. Consequently, two new sections are proposed, namely Tridimeris sect. Tridimeris and Tridimeris sect.
Zoque. A detailed description of the morphology of the genus is presented, including the description of the pollen, domatia
and its phylogenetic relationships. Taxonomic treatments of the species include synonyms, geographic and ecological notes,
comparisons with similar species and a preliminary assessment of their conservation status. All species of the genus are
potentially threatened with extinction and eight are assessed as Critically Endangered, which makes it the most threatened
lineage of Mexican trees. This study emphasizes the importance of scientific collections as invaluable sources of data for
current taxonomic revisions and conservation. It is a formal invitation to preserve and support the basic scientific research.
Keywords Cloud forest· IUCN red list· Miliuseae· Neotropics· Tropical rainforest
Introduction
Mexico, with around 30,000 species, of which ca. 50%
are endemic (Villaseñor 2016; Sosa etal. 2018; Molina-
Paniagua etal. 2023), is one of the megadiverse countries
in the world. This diversity is linked to its complex relief,
composed of geographic barriers and corridors, and strong
climatic seasonality combined with its prolonged isolation
from Central and South America (Wendt 1993; Ornelas
etal. 2013). Paradoxically, Mexico’s flora is also one of the
most threatened worldwide (see Samain etal. 2023) harbor-
ing three hotspots of biodiversity (Mittermeier etal. 2011).
More than 60% of its endemic trees are endangered (based
on IUCN red list criteria) and threatened by land-use change,
deforestation, unsustainable agriculture and excessive popu-
lation growth (Samain etal. 2023).
Handling Editor: Julius Jeiter.
* Andrés Ernesto Ortiz-Rodriguez
andres.ortiz@ib.unam.mx
1 Departamento de Botánica, Instituto de Biología,
Universidad Nacional Autónoma de México (UNAM),
CiudaddeMexico, Mexico
2 DIADE, Univ Montpellier, CIRAD, IRD, Montpellier,
France
3 Institut de Systématique, Evolution, Biodiversité
(ISYEB), Muséum National d‘Histoire
Naturelle-CNRS-SU-EPHE-UA, Paris, France
4 Missouri Botanical Garden, 4344 Shaw Blvd., St.Louis,
MO63110, USA
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A. E. Ortiz-Rodriguez etal.47 Page 2 of 32
The pantropical family Annonaceae with 110 genera
and ca. 2500 species is the most genus- and the third most
species-rich family within the Magnollidae clade (Couvreur
etal. 2011; Guo etal. 2017). In Mexico, 11 genera [Annona
L., Anaxagorea A. St.-Hil., Cymbopetalum Benth., Desmop-
sis Saff. (now including Stenanona Standl.), Guatteria Ruiz
& Pav., Mosannona Chatrou, Oxandra A. Rich., Sapranthus
Seem., Tridimeris Baill., Unonopsis R.E. Fr. and Xylopia L.]
and around 60 species are distributed, which in percentage
represent 32% of the genera and 6% of Neotropical species
(Erkens etal. 2017). More than half of their recorded spe-
cies and one genus, Tridimeris, are endemic. However, the
Annoanceae family is one of the least studied Magnoliidae
in Mexico and the taxonomic, ecological and phylogenetic
information about its species are scarce. Most of the taxo-
nomic revisions for the genera recorded in the country were
published between 1980 and 2000, often as thesis or scien-
tific articles (Erkens etal. 2017). Additionally, the major-
ity of recorded species were described based on specimens
collected prior to 1970 (based on own unpublished data).
As a result, current estimates of the species richness of the
Annonaceae family in Mexico may not be accurate, as recent
sampling and botanical exploration efforts have not been
taken into consideration.
Tridimeris is the only genus of Annonaceae endemic to
Mexico. However, it has largely neglected since its descrip-
tion by Baillon in 1869. Based on a flowering collection
by Ludwig Hahn (Hahn s.n.) from Veracruz, Mexico, the
genus Tridimeris, was characterized by its dimerous flow-
ers (two sepals and four petals) with one or two carpels, a
unique combination of morphological characteristics among
Neotropical Annonaceae genera (Schatz 1987; Couvreur
etal. 2012). Despite this, Standley (1922) only gave the
genus a cursory mention in his treatment of Annonaceae
for the Trees and Shrubs of Mexico. Then, during critical
revisions of the Neotropical genera of Annonaceae, Fries
(1931) determined another Hahn collection (Hahn 239) as
the fruiting stage of T. hahniana Baill., the type species of
the genus but also the only species described at that time
(Schatz 1987; Turner 2013). It is interesting to note that
the Hahn collection (Hahn 239) was originally identified
as the type specimen of a species named Uvaria hahniana
by Baillon in 1868. To avoid further confusion and provide
clarity in the identification of this species, Schatz (1994)
proposed the name T. baillonii for both Hann collections.
However, Turner (2013) determined that the correct name
for the species is T. hahniana Baill. (1869). This is because
the previously used binomial name, Uvaria hahniana Baill.
(1868), was a different name for the same species, while
T. baillonii G.E.Schatz (1994) is not a valid name (Turner
2013). It was also recognized that the type material comes
from the San Cristóbal hill in Orizaba, Veracruz, Mexico
(Schatz 1987). Thus, for nearly 90years, only the two Hahn
collections were recognized as representatives of the Mexi-
can genus Tridimeris, until a second species, T. chiapensis
M.A.Escobar & Ortiz-Rodr., was described (Ortiz-Rodri-
guez etal. 2016a) followed by T. huatuscoana Marinero-
Sobal & Ortiz-Rodr. (Ortiz-Rodriguez and Marinero-Sobal
2022) both from southern Mexico. These two new species
provided further confirmation that dimerous flowers and the
large, fleshy fruits are distinctive characteristics of Tridim-
eris. They also revealed that the genus diversity had been
previously underestimated.
We conducted a taxonomic revision of this poorly known
genus Tridimeris. We examined historical and recent her-
barium specimen collections and performed a phylogenomic
analysis using a hybrid-capture phylogenomic approach,
which consists of obtaining genetic information of the spe-
cies based on hundreds of nuclear markers designed exclu-
sively for the Annonaceae family (the Annonaceae bait kit;
Couvreur etal. 2019). Specifically, the three objectives of
our study were to (1) determine the species richness of the
genus Tridimeris; (2) infer the relationship between species;
and (3) determine the conservation status of each species.
Materials andmethods
Taxonomic revision
All bibliographic information on the genus Tridimeris was
compiled, including taxonomic revisions (Schatz 1987),
local and regional floras (Standley 1922; Ortiz-Rodriguez
etal. 2015), phylogenies (Ortiz-Rodriguez etal. 2016b) and
description of new species (Ortiz-Rodriguez etal. 2016a;
Ortiz-Rodriguez and Marinero-Sobal 2022). Analysis of this
bibliographic information resulted in a preliminary list of
Tridimeris species in Mexico. The list of species was evalu-
ated through an exhaustive review of herbarium specimens
deposited in the HEM, IEB, MEXU, MO, OAX, P and
XAL herbaria. This review was mainly focused on south-
ern Mexico, as this area is known for the distribution of
Annonaceae species in the country. In this way, synonyms
were detected, names were validated, andthe morphological
limits of each species were established. Also, new taxa were
recognized based on the combination of unique and distinc-
tive characters,a morphological species concept (Donoghue
1985; Stuessy 2009). Thespecies description following ter-
minology presented in Hickey (1973).
We analyzed the pollen, leaf and petals characteristics of
the Tridimeris species using scanning electron microscopy
(SEM) at the Photography and Microscopy of the Biodi-
versity Laboratory 1, Universidad Nacional Autónoma de
México (UNAM). The flowering material for SEM was col-
lected and preserved in alcohol 70%. The material was dehy-
drated with gradual alcohol (ethanol) solutions at 70%, 80%,
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 3 of 32 47
96% and 100%, 24h each. The leaves were analyzed directly
from herbarium specimens. All the material was dried to the
critical point using CO2, placed on aluminum sample holders
and covered with a layer of gold. Finally, specimens were
observed under a scanning electron microscope (Hitachi-
SU1510, Tokyo, Japan) at a voltage of 10 or 15 kw.
Phylogenetic relationships
Phylogenetic relationships among the 10 Tridimeris species
(all species here recognized) were inferred using a hybrid-
capture phylogenomic approach using the Annonaceae-spe-
cific baiting kit for DNA sequencing (Couvreur etal. 2019;
Nge etal. 2024). This kit has been designed to capture 469
orthologous exons that are present in Annonaceae species.
As an outgroup, we included representatives of the genus
Sapranthus Seem, which has been widely supported as the
sister group of the genus Tridimeris (Nge etal. 2024;Ortiz-
Rodriguez etal. 2016b) and the Asian genus Wuodendron
B.Xue, Y.H.Tan & Chaowasku as the sister to the tribe
Sapranthinae. DNA was extracted directly from leaf samples
of herbarium-preserved specimens with a collection year
ranging between 1865 and 2022 (Table1). DNA extrac-
tion, library preparation and sequencing protocols, as well
as the bioinformatic pipelines, are presented in Couvreur
etal. (2019), Brée etal. (2020) and Dagallier etal. (2023).
We used HybPiper v1 (Johnson etal. 2016) to analyze the
read data and eliminate potential paralogues. Briefly, the
reads were mapped onto the corresponding exons, where the
reads successfully assigned to each region were assembled
into contigs. Contigs that showed overlap were combined
into supercontigs. Alignments were trimmed to remove
poorly aligned regions, introns and intergenic regions. Then,
potential paralogs (multiple contigs that map well to a single
reference sequence) were analyzed separately by construct-
ing gene trees and those loci showing conflicting relation-
ships were eliminated.
Two different strategies were used for phylogenetic analy-
sis: a concatenated-based approach and a gene tree approach
(see Dagallier etal. 2023). In each approach, a dataset that
covered 75% of each exon for 75% of all individuals sampled
was used (75/75 ratio; Couvreur etal. 2019). For the analysis
based on the concatenated data matrix, phylogenetic trees
were inferred using the maximum likelihood implemented in
RAxML v.8.2.12 (Stamatakis 2014) with the “-f a” option,
100 bootstrap replicates and the GTRGAMMA model. For
the gene tree approach, we also inferred a phylogenetic tree
for each supercontig using RAxML 8.2.9 (Stamatakis 2014)
under the GTRGAMMA model and 100 bootstrap replicates
Then, we inferred the summary species tree in ASTRAL-III,
v5.5.11 under the multi-species coalescent model (Zhang
etal. 2018). The support at the branches was estimated both
with the quartet support (QS) values (“-t 1” option) and with
the local posterior probabilities (LPP) (default parameters).
The species tree was then rooted on Wuodendron praecox.
Both phylogenetic hypotheses were then plotted and anno-
tated using the ape and phytools R-packages (Paradis and
Schliep 2019; Revell 2024). The paired fastq sequences for
individuals included in this study are available in Genbank
SRA under Bioproject number PRJNA508895 (http:// www.
ncbi. nlm. nih. gov/ biopr oject/ 508895).
Conservation status
The distribution area of each species was determined based
on the geographic information of the collection locations
recorded on the herbarium specimens studied. In this way,
each locality is associated with a collection. We assessed
Table 1 Herbarium specimens
of the species included in the
phylogenetic analyses. The
length in base pairs of the DNA
alignment is provided
Species Specimens Collection year Herbaria Pb alignment
Sapranthus campechianus A.E. Ortiz-Rodríguez 1321 2021 MEXU 361,830
Sapranthus microcarpus A.E. Ortiz-Rodríguez 1320 2021 MEXU 361,750
Sapranthus palanga W.D. Stevens 32796 2012 MO 357,400
Sapranthus violaceus W.D. Stevens 28423 2009 MO 361,577
Sapranthus viridiflorus P.J.M. Maas 9402 2004 U 359,515
Tridimeris chiapensis H. Gómez 3862 2021 MEXU 357,047
Tridimeris crotalocarpa A. Campos 1491 1988 MEXU 360,478
Tridimeris globosa J. I. Calzada 16988 1991 MEXU 360,998
Tridimeris hahniana L. Hahn s.n 1865 P 255,519
Tridimeris huatuscoana E.J. Marinero-Sobal 425 2022 MEXU 362,266
Tridimeris nebulosa G. E. Schatz 1198 1986 MO 361,706
Tridimeris cauliflora J. Rivera 2059 1999 MO 361,465
Tridimeris tuxtlensis G. Ibarra 235 1982 MEXU 362,014
Tridimeris uxpanapensis K. Lagos 16 2019 MEXU 362,110
Tridimeris vilosa G. Ibarra 3779 1992 MEXU 361,017
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A. E. Ortiz-Rodriguez etal.47 Page 4 of 32
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 5 of 32 47
the preliminary conservation status of each species by cal-
culating its extent of occurrence (EOO), area of occupancy
(AOO) and number of localities using the ConR R-package
(Dauby et al. 2017). For this analysis, locations were defined
on the default value of 30 km2 cell size. We used these statis-
tics to carry out a preliminary conservation assessment using
the IUCN Red List criterion B based on the geographic dis-
tribution of species (IUCN 2022).
Results
Taxonomic revision
Ten species of Tridimeris are recognized here, of which six
(T. cauliflora, T. crotalocarpa, T. globosa, T. tuxtlensis, T.
uxpanapensis and T. villosa) are described as new and a new
name (T. nebulosa) is proposed. All species areendemic to
Mexico (Fig.1a).
General morphology
Habit: Small- to medium-sized evergreen trees, usually less
than 10m tall, rarely reaching 25m in T. nebulosa and T.
tuxtlensis. The main trunk is more or less robust, and in the
species for which diameter has been recorded, it is usually
between 10 and 20cm, rarely to 30cm in T. nebulosa. Twigs
and slender branches are sparsely pubescent when young,
becoming glabrous with age. Only in T. villosa, the twigs
remain pubescent in older age.
Leaves: Leaves are simple, entire, petiolate and estipu-
late, arranged alternately in a single plane along lateral
branches (distichous), usually shiny and dark green invivo
and greenish gray or olive green when dry. The petioles are
swollen and canaliculated above, ranging from 2 to 5mm
long, very sparsely to densely covered by golden-brown
hairs, usually darkened when dry. The shape of the lamina
is elliptic to narrowly elliptic, rarely lanceolate in T. cro-
talocarpa (Fig.2a–j). The texture of the lamina is membra-
nous to slightly coriaceous, the surface smooth to slightly or
partially verruculose, sometimes with black or brown dots
(often visible only under stereomicroscope).
The lamina varies in length, from 10 to 25cm in most
species except in T. crotalocarpa and T. globosa which are
smaller than 10cm. The base of the lamina is acute to atten-
uate (sometimes rounded in T. crotalocarpa, T. nebulosa
and T. villosa) and often slightly asymmetric (Fig.2a–j).
The apex of the lamina is generally acute to acuminate, the
acumen up to 35mm long. The primary vein is distinctly
impressed above and raised below. The venation is eucamp-
todromous to weakly brochidodromous with usually 5–10
secondary veins per side (only T. villosa has leaves with
10–17 secondary veins per side). In almost all species the
leaves have pocket domatia in the axils of the secondary
veins (only absent in T. crotalocarpa), which are usually
glabrous, with some hairs around the mouth (T. cauliflora)
or with stiff hairs inside the cavity (setaceous) as in T. hahni-
ana, T. huatuscoana and T. globosa (Fig.3a–f). The tertiary
venation is usually reticulate or sometimes intermediate,
between reticulate and percurrent.
The indumenta on petioles and lamina is composed of
simple, appressed or erect hairs. Most species of Tridimeris
have completely glabrous leaves or nearly so with hairs only
present along the midrib or on the domatia, or in a very scat-
tered way and almost imperceptible. Tridimeris villosa is the
only species with leaves being densely covered with both
appressed and erect light brown hairs below.
Inflorescences: Inflorescences are axillary, reduced rhipi-
dia, generally bearing a single flower (Fig.4a–g). Tridimeris
huatuscoana has a 2-flowered inflorescence occurring on
short shoots with the flowers in succession. Cauliflory is
only known to occur in T. cauliflora, where the inflores-
cences are borne along the main trunk. The peduncle (the
bracteate axis that supports the flowers) is very short and
poorly differentiated in T. chiapensis and T. tuxtlensis and
as a short shoot about 1mm long in T. huatuscoana, T. hah-
niana, T. globosa and T. nebulosa. If the peduncle is not
differentiated, the base of the pedicel bears 1 rarely 2 tiny
bracts; otherwise, a short shoot bears 2–5 tiny bracts in suc-
cession. Bracts are ciliated and sparsely to densely pubes-
cent. Pedicels (including the peduncle) vary in length from 1
to 20mm long with the shortest pedicels found in T. huatus-
coana, T. globosa, T. nebulosa and T. villosa (1–3mm), and
the longest in T. chiapensis, T. hahniana and T. tuxtlensis
(10–20mm). The pedicels are glabrous or nearly so in most
species and densely covered with golden-brown hairs only
in T. huatuscoana, T. nebulosa and T. villosa (Fig.4a–g).
In fruit, the pedicel becomes thicker, but does not grow in
length.
Flowers: Only six species (T. chiapensis, T. globosa, T.
huatuscoana, T. hahniana, T. nebulosa and T. tuxtlensis)
have been collected with flowers, and the remaining four
species are known only from fruiting specimens. Tridim-
eris is unique among Neotropical Annonaceae in having
dimerous flowers (Fig.4a–g). Flowers have 2 connate and
Fig. 1 Distribution and phylogenetic relationships of Tridimeris spe-
cies. a Geographic distribution of the species belonging to the T. sect.
Tridimeris (circles) and T. sect. Zoque (stars). b Maximum likelihood
tree (RaxML) based on 290 Annonaceae wide exons. Blue circles
indicate strongly supported clades (bootstrap values = 100); the bars
indicate the position of the T. sect. Tridimeris (blue) and the T. sect.
Zoque (reddish). On the right, photographs of the flowers of T. chia-
pensis (at the top) as a representative of the T. sect. Zoque and the
flower of T. nebulosa (at the bottom) as a representative of the T. sect.
Tridimeris
◂
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A. E. Ortiz-Rodriguez etal.47 Page 6 of 32
ciliate sepals, and 4 free petals in 2 equal to subequal whorls,
petals are green or yellowish green in most species, only
cream or white in T. huatuscoana (Fig.4a–g). The aesti-
vation of the petals is imbricate. The torus is convex and
densely covered with erect hairs. Sepals are broadly ovate
to orbicular, rounded at apex, glabrous (in T. chiapensis, T.
hahniana, T. globosa and T. tuxtlensis) to densely covered
by appressed golden-brown hairs outside (in T. huatuscoana
and T. nebulosa), glabrous inside, the margins always cili-
ate, 2–3mm in length. Petals are usually rigid (thick) and
without obvious venation at anthesis, deltoid (in T. huatus-
coana and T. nebulosa), orbicular (in T. hahniana) or elliptic
to oblong (in T. chiapensis and T. tuxtlensis), sparsely to
densely covered by golden-brown hairs outside or glabrous,
or with hairs only on the margins (ciliate) as in T. chiapen-
sis and T. tuxtlensis, glabrous inside, acute to rounded at
Fig. 2 Variation in shape and
size of Tridimeris leaves. a
Tridimeris tuxtlensis [speci-
men: A. Rincón 2359 (MEXU)].
b Tridimeris cauliflora [B.
Boyle, A. Boyle and A. Montes
3879 (MEXU)]. c Tridim-
eris chiapensis [specimen:
M.A. Escobar-Castellanos
689 (MEXU)]. d Tridimeris
tuxtlensis [specimen: R. Torres
2105 (MEXU)]. e Tridimeris
villosa [specimen: G. Ibarra
3779(MEXU)]. f Tridimeris
crotalocarpa [specimen: A.
Campos 1839 (MEXU)]. g Tri-
dimeris nebulosa [specimen: L.
Hurtado 717 (MEXU)]. h Tridi-
meris crotalocarpa [specimen:
A. Campos 1491 (MEXU)]. i
Tridimeris huatuscoana [speci-
men: E.J. Marinero-Sobal 426
(MEXU)]. j Tridimeris globosa
[specimen: E.J. Marinero-Sobal
426 (MEXU)]. Drawn by Robin
Pérez Lucas
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 7 of 32 47
apex, only long aristate in T. huatuscoana, the base truncate
and cusped around the stamens. Inner petals usually with a
shallow, more or less triangular white patch near the base
inside (a food body), absent or linear-curved in T. nebulosa
(Fig.5a–b). Stamens are relatively numerous, around 50,
with a very short filament and the apical part of connective
expanded over the thecae, shield-shaped, ellipsoid to angu-
late, glabrous. Carpels are free, being few in number and
varying between 1 and 5. The stigma is sessile, spherical
to napiform to flattened ellipsoid. It is attached to the ovary
obliquely. Each carpel has 10–20 lateral ovules arranged in
two rows (biseriate).
Pollen grains: Pollen grains are solitary, symmetrical,
elliptic, with two depressed germinative zones, but inapertu-
rate, 30–55μm long, 25–30μm wide. The exine sculpturing
is weakly rugulate to fossulate (-perforate) ornamentation.
The pollen of T. tuxtlensis is smaller (~ 30μm) and rather
globose with strongly rugulate to fossulate (-perforate)
Fig. 3 Pocket domatia in the axils of the secondary veins: a glabrous
domatia densely covered with long hairs (Tridimeris villosa); b gla-
brous domatia (T. chiapensis); c glabrous domatia slightly covered by
long hairs (T. tuxtlensis); d setose domatia (T. huatuscoana); e doma-
tia absent (T. crotalocarpa); f glabrous domatia (T. nebulosa)
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A. E. Ortiz-Rodriguez etal.47 Page 8 of 32
ornamentation, which distinguishes it very well from the
other species (Fig.5c, d).
Fruits: Fruits are apocarpous (free carpels in flower
and fruit) as for most Annonaceae. They cluster into 1 or 3
indehiscent, spheroid (in T. globosa and rarely in T. nebu-
losa) to cylindrical monocarps, with a short stipe (Fig.6a–i).
The monocarps vary in length, from 40 to 100mm, usu-
ally more than 20mm diam, with two alternating rows of
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 9 of 32 47
5–10 seeds. The monocarps are glabrous in T. cauliflora,
T. crotalocarpa, T. chiapensis, T. huatuscoana, T. globosa,
T. tuxtlensis and T. uxpanapensis, and densely covered by
golden-brown hairs (velvety) in T. nebulosa and T. villosa.
The monocarps are green, brown or yellow, the mesocarp
is thick and so the fruit appears smooth when dry, when
thinner the mesocarp is slightly to strongly constricted
between the seeds (in T. cauliflora and T. crotalocarpa) or
rarely wrinkled (only in T. nebulosa) or forming longitudinal
folds (in T. chiapensis, T. tuxtlensis and T. uxpanapensis).
Seeds are usually spherical wedge-shaped, around 20mm in
length, smooth and with lamellate endosperm ruminations.
Phylogenetic inference
After filtering for the 75/75 ratio, and deleting potential par-
alogues, our dataset contained a total of 230 genes which
we used for the phylogenetic analyses. The number of base
pairs of the alignment varied between 362,266 and 255,519,
with T. huatuscoana with the longest alignment length and
T. hahniana with the shortest, both species representing the
most recent and oldest collected plant tissues, respectively
(Table1). The resulting maximum likelihood and ASTRAL
trees recovered the same topology and were maximally sup-
ported at all levels (Fig.1b; Supplementary material 1).
The genus Tridimeris is monophyletic, and it is divided
into two strongly supported subclades (Fig.1b). The first
subclade consists of T. huatuscoana, T. hahniana (the type
species of the genus), T. globosa, T. nebulosa and T. vil-
losa (BP = 100). The second subclade includes the rest of
the species, T. cauliflora, T. chiapensis, T. crotalocarpa, T.
tuxtlensis and T. uxpanapensis (BP = 100).
Conservation status
Based on our preliminary IUCN assessments, we show that
all 10 species of Tridimeris are threatened by extinction,
with an incredible 8 species assessed as potentially Critically
Endangered (Table2) under criterion B.
Discussion
Hidden species richness andrestricted distribution
inTridimeris
In this study, six new species of Tridimeris are described,
raising the number of species from three to ten. For five of
the new species, all the specimens analyzed were collected
more than 25years ago, which emphasizes the importance
of modern herbarium revision work for documenting the
species richness in Mexico. It also confirms that a significant
portion of the yet-to-be-known Mexican plant diversity is
preserved in herbaria (Bebber etal. 2010; Villaseñor 2015).
Even so, Tridimeris have been poorly collected in Mexico
and four species are known only from fruiting material. This
is probably associated with the fact that the small, inconspic-
uous flowers of Tridimeris species could be difficult to detect
during field trips. Thus, species delimitation in Tridimeris,
as presented here, is based mainly on the variation of fruit
and leaf characteristics. All Tridimeris species are endemic
to Mexico and are an infrequent and rarely collected floristic
element across the country. Furthermore, for most species
only one or two localities are known (Fig.1a). Tridimeris
species inhabit humid forests of lower and mid-altitude (seal
level to 1900m) such as evergreen forests or montane cloud
forests, mostly on karstic soils. In these types of vegetation,
local diversity consists of rare or infrequent species, with
a high species turnover between localities (González-Espi-
nosa etal. 2006). The Tridimeris species distribution pattern
shows that there are no sympatric species in the genus except
for T. nebulosa and T. huatuscoana that co-occur in sympa-
try in one part of their distribution (Fig.1a).
The species richness of the Mexican genus Tridimeris
is now comparable with that of its sister group the genus
Sapranthus (ten species: Schatz etal. 2018) and thus one of
the most diverse Annonaceae genus in Mexico. Furthermore,
all Tridimeris species are endemic to this country. Therefore,
the genus Tridimeris represents an important plant lineage
in Mexico and deserves recognition after years of neglect.
Systematics ofTridimeris
The phylogenetic hypothesis of Tridimeris includes all the
species here recognized, including recently collected sam-
ples but also historical samples collected more than 25years
ago, or in the case of Tridimeris hahniana samples collected
155years ago (Table1). These results show that herbarium
collections are a valuable data source for studies of plant
phylogeny, ecology and evolution (Bakker etal. 2020; Davis
Fig. 4 Inflorescences and flower morphology in Tridimeris. a Basic
morphology of the flowers and inflorescences, flowers generally soli-
tary, pedicels with one or more minute bracts at the base and sepals
fused with ciliated margin (T. globosa). b Flowers of T. sect. Tridi-
meris, bracts, peduncles and sepals densely covered with short hairs.
c Inner petals of T. huatuscoana, long, aristate petals with a more or
less triangular opening (food body) at the base inside. d Inner pet-
als of T. nebulosa, petals deltoid with a more or less linear opening
(food body) at the base inside. e Flowers of T. sect. Zoque, bracts,
peduncles and sepals glabrous or nearly so. f Inner petals of T. tux-
tlensis, petals lanceolate or linear-triangular, obtuse to rounded at the
tip, margin ciliate, with a more or less triangular opening (food body)
at the base inside. G Inner petals of T. chiapensis, petals lanceolate or
linear-triangular, obtuse to acute at the tip, margin ciliate, with a more
or less triangular opening (food body) at the base inside. Drawn by
Robin Pérez Lucas
◂
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A. E. Ortiz-Rodriguez etal.47 Page 10 of 32
2023). The extraction of genetic information from herbarium
samples allowed the inclusion of all Tridimeris species in
our phylogenetic reconstruction, even those in difficult-to-
access locations, as well as historical or poorly collected
specimens (Table1).
Based on the complete sampling of Tridimeris species,
our phylogenomic analysis supports two subclades within
the genus (Fig.1b). We thus refine the classification of the
genus by erecting two sections (see Taxonomic treatment
for details): sect. Tridimeris (clade 1: T. huatuscoana, T.
hahniana, T. globosa, T. nebulosa and T. villosa) and sect.
Zoque (clade 2: T. cauliflora, T. chiapensis, T. crotalo-
carpa, T. tuxtlensis and T. uxpanapensis). Members of sec-
tion Tridimeris exhibit noticeable morphological variation,
yet they possess a distinct combination of characteristics.
The key distinguishing features of this section include
the setose leaf domatia, pedicels with usually 2 to 3 tiny
bracts, almost sessile flowers with deltoid to orbicular pet-
als and 1 or 2 carpels per flower. In two sister species (T.
nebulosa and T. villosa), the domatia are glabrous, but
the flowers are almost sessile and with deltoid petals as
in other species (T. huatuscoana). Furthermore, they are
the only two species in the entire genus with fruit surfaces
densely covered by golden-brown hairs (velvety). Tridi-
meris hahniana is the only species in this section with
long pedicels (up to 20mm), but like its sister species, T.
globosa, it retains the setose leaf domatia, and its flowers
have orbicular petals with 1 or 2 carpels. Additionally, the
members of this section are distributed toward the west of
Mexico (Fig.1a). The members of section Zoque are dis-
tinguished by the combination of glabrous pocket domatia
and long, glabrous, pedicellate flowers and fruits. Moreo-
ver, two sister species (T. cauliflora and T. crotalocarpa)
with fruit walls strongly constricted between the seeds
form part of this clade. The only two species for which
flowers are known show characteristics different from spe-
cies of section Tridimeris such as elliptic and flattened pet-
als with a ciliated margin. In contrast to sect. Tridimeris,
Fig. 5 Inner petals and pollen grains of Tridimeris as seen in the
scanning electron microscope. a Inner petals of T. tuxtlensis, at base
inside, a more or less triangular opening (food body) filled with pol-
len grains. b Inner petals of T. hahniana, at base inside, a more or less
linear opening (food body) filled with pollen grains. c Pollen grain
from T. chiapensis, solitary, symmetrical, elliptic, with two depressed
germinative zones, but inaperturate, exine sculpturing weakly rugu-
late to fossulate (-perforate) ornamentation. d Pollen grain from T.
tuxtlensis, solitary, symmetrical, globose, with two depressed germi-
native zones, but inaperturate, exine sculpturing strongly rugulate to
fossulate (-perforate) ornamentation
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 11 of 32 47
species of sect. Zoque are distributed toward the south of
Mexico (Fig.1a).
The phylogenetic hypotheses proposed so far (Chatrou
etal. 2012; Chawasku etal. 2014; Guo etal. 2017; Nge etal.
2024;Ortiz-Rodriguez etal. 2016b) recovered Tridimeris
sister to the dry forest-adapted genus Sapranthus, with high
support values (Fig.1b). Both genera share synapomor-
phies such as the large and fleshy monocarps with numer-
ous lamellar ruminate seeds and the presence of the pocket
domatia in the axils of secondary veins (Table3). However,
Sapranthus has the typical Annonaceae flower structure with
three free sepals and two whorls of three petals, several car-
pels per flower and terminal (leaf-opposed) inflorescences
(Schatz etal. 2018).
Tridimeris is estimated to have originated (stem node)
about 12 million years ago (Ma) with subsequent diversifi-
cation with its sister genus Sapranthus from the late Mio-
cene to the Pliocene (11–3Ma, Ortiz-Rodriguez etal. 2018).
This period in Mexico is characterized by a strong climatic
change and orogenic activity (Toledo 1982; Wendt 1993).
The pattern of distribution and divergence times estimates
of Tridimeris and Sapranthus, is consistent with the Palaeo-
american cenocron (Morrone 2015; Halffter and Morrone
2017; Gutierrez-Ortega etal. 2018), defined as lineages that
diversified before the Pliocene and with current representa-
tives distributed in the montane deserts, tropical dry forest
or tropical rainforests of Mexico. The diversification of these
lineages has been linked to processes of ecological diver-
gence promoted by the uplift of mountain regions and the
expansion of most North American deserts (see Gutierrez-
Ortega etal. 2018; Ortiz-Rodriguez etal. 2020). Thus, the
occupation or invasion of drier tropical forests by Sapran-
thus and the persistence of Tridimeris in the wet forest may
have favored genetic isolation and ecological and morpho-
logical differentiation among sister genera.
Conservation status
Based on our preliminary IUCN assessments, we show that
all 10 species of Tridimeris are threatened by extinction
under criterion B (Table2). As the evolutionary origin of
Tridimeris has been estimated about 12 million years ago
(see Ortiz-Rodriguez etal. 2018), it must be considered a
highly threatened clade of vital importance for conservation
actions across the country. This is because species of Tridi-
meris have a very restricted distribution with very few col-
lections to date (Fig.1a). In addition, species are restricted
to medium (max 1900m) and low altitudes where moun-
tain cloud forest and tropical rainforest occur, both forest
types being seriously threatened in Mexico (Samain etal.
2023). Our results (Table2) show that most species have a
single location (sensu IUCN 2022). In only two species (T.
chiapensis and T. tuxltensis), the type locality is within the
geographic limits of a protected natural area. Half of the
species were last collected more than 30years ago (Table2)
and are only known from a few herbarium specimens. An
extreme case is the species T. hahniana (the type of the
genus), which is only known by the type collected 150years
ago. However, the type locality may still hold some individu-
als and should be the focus of future botanical exploration.
Furthermore, most of the known locations for the species are
found in sites with accelerated rates of land-use change and
forest overexploitation, being restricted to patches of forest
surrounded by roads, croplands and cattle pastures.
Taxonomic treatment
Tridimeris Baill., Adansonia 9: 219. 1869. 1841.—
TYPESPECIES: Tridimeris hahniana Baill.
Description:Small- to medium-sized trees, 10–25m tall,
evergreen; young twigs terete, initially sparsely covered with
simple, erect to appressed hairs, becoming glabrous with age
or rarely remaining pubescent. Leaves alternate, distichous,
simple, entire, petiolate, estipulate; petiole short and swol-
len, often blackened, canaliculate; lamina 5–25 × 2–8cm,
elliptic to rarely narrowly lanceolate, membranous to slightly
coriaceous, smooth to slightly verruculose, glabrous on both
sides, rarely sparsely to densely covered with appressed
and erect hairs below, base cuneate to rounded, sometimes
barely asymmetrical, apex obtuse to acuminate, primary
vein impressed above, venation eucamptodromous to weakly
brochidodromous with 5–17 secondary veins per side, and
with glabrous or setose pocket domatia present in the axils
of the secondary veins with the primary vein below, ter-
tiary venation usually reticulate. Inflorescences a condensed
rhipidium, axillary or rarely cauliflorous and borne on the
main trunk, the peduncle poorly differentiated or as a short
shoot about 1mm long; pedicels and outer side of bracts,
sepals and petals glabrous or sparsely to densely covered
with appressed golden-brown hairs. Flowers solitary or two
flowers in succession, bisexual, dimerous, flowering pedicel
bearing at the base, 1 or 5min, ciliated bracts; flower buds
conical (pyramidal), rarely globose; sepals 2, ciliate along
the margins, ovate to orbicular, connate at the base, opposite,
somewhat stiff, with non-obvious venation; petals 4, free, in
2 subequal whorls, imbricate, longer than the sepals, deltoid
or elliptic, rarely orbicular, somewhat stiff with non-obvious
venation invivo, green, yellowish green or rarely white, usu-
ally the inner petals bearing a triangular, rarely linear, white
patch at their base inside; stamens filaments very short, not
septate, the anther connective tissue expanded above the
thecae, shield-shaped, ellipsoid to angulate; pollen grains
solitary, symmetrical, elliptic, with 2 depressed germinative
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A. E. Ortiz-Rodriguez etal.47 Page 12 of 32
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 13 of 32 47
zones, but inaperturate, exine sculpturing weakly to strongly
rugulate to fossulate (-perforate) ornamentation; staminodes
rarely present; carpels 1–5, free, style absent or rarely very
short, stigma spherical to napiform to flattened ellipsoid,
attached to the ovary obliquely; ovules 10–18 in two rows.
Fruits apocarpous, 1–3 monocarps, cylindrical or globose,
large and fleshy, indehiscent, sessile to shortly stipitate;
seeds 8–30 per monocarp, in two alternating and sometimes
interdigitating rows, spherical wedge-shaped or flattened
ellipsoid, pale brown to orange-brown, smooth, endosperm
ruminations lamellate.
Species richness and distribution: Ten species, all endemic
to Mexico.
Etymology: The name of the genus refers to its flower struc-
ture, "three whorls of two components each (two sepals and
four petals in two whorls)."
Infrageneric classification
Tridimeris sect. Tridimeris—TYPESPECIES: Tridimeris
hahniana Baill.
Diagnosis:Leaf domatia setose or rarely glabrous; inflores-
cences axillary, 1-flowered or 2-flowered, peduncle usually
as a short shoot about 1mm long, usually 2–3 basal bracts.
Flowers almost sessile, rarely long pedicellate, petals del-
toid, rarely orbicular, often strongly concave at the base,
forming a cusp that fits tightly around the stamens. The
external surface of the sepals and petals glabrous or densely
covered by golden-brown hairs, margin glabrous or rarely
ciliate. 1–2carpels per flower. Monocarps densely covered
by golden-brown hairs or glabrous.
Species included: Tridimeris hahniana Baill, T. huatuscoana
Marinero-Sobal & Ortiz-Rodr., T.ridimeris globosa Ortiz-
Rodr., T. nebulosa Ortiz-Rodr. and T. villosa Ortiz-Rodr.
Distribution: Eastern Mexico, in the area of Tuxtepec Oax-
aca, in the region of Orizaba-Zongolica, Veracruz, and along
the Sierra Madre Oriental, from the center of Veracruz to
San Luis Potosí.
Tridimeris sect. Zoque Ortiz-Rodr. & Couvreur, sect.
nov.—TYPE SPECIES: Tridimeris chiapensis Escobar-
Castellanos & Ortiz-Rodr.
Diagnosis:Leaf domatia glabrous or rarely with a few hairs
around the mouth but not inside the cavity (not setose);
inflorescences axillary or rarely borne along the main trunk
(cauliflorous), 1-flowered, peduncle minute and poorly dif-
ferentiated, 1–2 basal bracts. Flowers long pedicellate, petals
elliptic or oblong-elliptic, flattened. The external surface of
the sepals and petals glabrous, margins ciliate. Carpels 2–5
per flower, rarely 1. Monocarps glabrous.
Species included: Tridimeris cauliflora G.E.Schatz, T. chia-
pensis Escobar-Castellanos & Ortiz-Rodr., T. crotalocarpa
Ortiz-Rodr., T. tuxtlensis G.E.Schatz, T. uxpanapensis
G.E.Schatz.
Distribution: Southern Mexico, in Chiapas, Sierra de Juarez
in Oaxaca and in the region of Los Tuxtlas and Uxpanapa,
in Veracruz.
Key tospecies ofTridimeris
1a Leaves, petioles and twigs densely covered with long,
light brown hairs, discernible to the naked eye and to
the touch; lamina with more than 10 secondary veins
per side; leaf base rounded……… ……… T. villosa
1b Leaves, petioles and twigs glabrous or nearly so, if
hairs present, not visible to the naked eye or discern-
ible to the touch (then glabrous in appearance); lamina
with less than 10 secondary veins per side; leaf base
acute to attenuate………...2
2a Pocket domatia in the axils of the secondary veins
present; leaves more than 10 cm long (only in T. glo-
bosa leaves less than 10 cm); fruit wall smooth, wrin-
kled, forming longitudinal folds or rarely constricted
between seeds (only in T. cauliflora)….……… ………
……… …………..……..……..…3
2b Pocket domatia in the axils of the secondary veins
absent; leaves less than 10 cm long; fruit wall strongly
constricted between seeds…….……… T. crotalo-
carpa
3a Pocket domatia setose (a dense number of long and
often rigid hairs inside the domatia bag)….………
……… ……….…..4
3b Pocket domatia glabrous or rarely with a few hairs
around the mouth (only in T. cauliflora) but not inside
Fig. 6 Dry fruits of Tridimeris, variation in shape, size and surface.
a Fruits of T. nebulosa, cylindrical monocarps with a strongly folded
surface and densely covered with short hairs (velvety). b Fruits of T.
villosa, cylindrical monocarps with a smoot surface and densely cov-
ered with short hairs (velvety). c Fruits of T. nebulosa, globose mono-
carps with a strongly folded surface and densely covered with short
hairs (velvety). D Fruits of T. globosa, globose monocarps with a
smooth, glabrous surface. e Fruits of T. chiapensis, cylindrical mono-
carps with a slightly folded, glabrous surface. f Fruits of T. huatus-
coana, tuber-shaped monocarps with a smooth, glabrous surface. g–h
Fruits of T. tuxtlensis, cylindrical monocarps with a glabrous surface
and the wall slightly constricted between the seeds. i Fruits of T. cro-
talocarpa, cylindrical monocarps with a glabrous surface and the wall
strongly constricted between the seeds. Drawn by Robin Pérez Lucas
◂
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A. E. Ortiz-Rodriguez etal.47 Page 14 of 32
the domatia bag (not setose) ………....……… ………
……… ……… ……… ……… ………...………5
4a Flowers with pedicels 10–20 mm long ………..….T.
hahniana
4b Flowers with pedicels 1–3 mm long……… ………
……… …………..6
5a Inflorescences cauliflorous, borne along the main
trunk………..……… ………T. cauliflora
5b Inflorescences ramiflorous, axillary, borne on the
branches among foliage……… …………..7
6a Leaves less than 10 cm long, the apex acumen less
than 10 mm long; 1-flowered inflorescences, pedicels,
sepals and petals sparsely covered with golden-brown
hairs or glabrous; fruits globose……...T. globosa
6b. Leaves more than 10 cm long, the apex acumen 10–15
mm long; 2-flowered inflorescences, pedicels, sepals
and petals densely covered with golden-brown hairs;
fruits cylindrical………….T. huatuscoana
7a. Flowering pedicels 10–17 mm long; sepals and petals
glabrous; petals elliptic to oblong-elliptic, flattened;
inner petals with a triangular patch/opening at base
inside; fruit surface glabrous or nearly so, black when
dry………...……………8
7b. Flowering pedicels 2–5 mm long; sepals and petals
densely covered with golden-brown hairs; petals del-
toid, strongly concave at the base; inner petals with
a linear opening at base inside; fruit surface velvety,
golden brown when dry……… ……… ………T. nebu-
losa
8a. Leaves broadly elliptic, 4─8 cm wide, monocarps
more than 80 mm long……… ……… ……… ………
…………...……… ……… ……… …………9
8b. Leaves narrowly elliptic, 2─3 (5) cm wide; monocarps
less than 50 mm long……… ……… ……… ………
………….…...T. uxpanapensis
9a. Acumen of leaves 8–10 mm long; carpels 1 or 2 per
flower; apex of petals obtuse to rounded……… ………
……… ……… ………T. tuxtlensis
9b. Acumen of leaves 12–15 mm long; car-
pels 3 to 5 per flower; apex of petals
acute.……………..……….…..T. chiapensis
Tridimeris chiapensis Escobar-Castellanos & Ortiz-Rodr.,
PhytoKeys 74: 86–89, f. 1–3. 2016.—TYPE: Mexico, Chia-
pas, Municipio de Berriozábal, Zona Sujeta a Protección
Table 2 Morphological
characteristics of Tridimeris
compared with those of their
phylogenetically closest genera
(subtribe Sapranthinae)
Features Tridimeris Desmopsis Sapranthus
Inflorescences Axillary Terminal Terminal
Sepals 2, fused 3, rarely 4, free or fused 3, free
Petals 4, free 6, rarely 8, free or fused 6, free
Carpels 1 or 2, rarely 5 10 or more 10 or more
Ovules Biseriate Uniseriate, rarely biseriate Biseriate
Domatia Present Absent Present
Monocarps Large thick-walled small rarely large, thin- or thick-
walled
Large thick-walled
Seeds ruminations Lamellate Spiniform to peg-shaped Lamellate
Table 3 Preliminary IUCN
conservation assessments
for all the Tridimeris species
under criterion B (D for T.
tuxtlensis). For each species,
the area of occupancy (AOO)
and the extent of occurrence
(EOO) were calculated, as
NA when the value could not
be determined. The number
of locations sensu IUCN is
provided (estimated by ConR;
see methods) and the year
of the last known herbarium
collection. The details for each
assessment are provided in
species description section
Species EOO AOO Number
of loca-
tions
Last collection Preliminary IUCN category
Tridimeris chiapensis 8 8 1 2016 CR B1ab (i, ii, iii) & B2 ab (i, ii, iii)
Tridimeris crotalocarpa NA 8 2 1988 CR B2 ab (ii, iii, iv)
Tridimeris globosa NA 4 1 1991 CR B2 ab (ii, iii)
Tridimeris hahniana NA 4 1 1869 CR B2 ab (ii, iii)
Tridimeris huatuscoana NA 4 1 2022 CR B2 ab (ii, iii, v)
Tridimeris nebulosa 14130 16 4 2022 EN B2 ab (i, ii, iii, iv)
Tridimeris cauliflora NA 4 1 1999 CR B2 ab (ii, iii,v)
Tridimeris tuxtlensis 13 12 2 2005 VU D2
Tridimeris uxpanapensis NA 8 2 2019 CR B2 ab (ii, iii,v)
Tridimeris villosa NA 4 1 1992 CR B2 ab (ii, iii,v)
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 15 of 32 47
Ecológica “La Pera,” Campamento “Trepatroncos” carret-
era Berriozábal-Joaquín Miguel Gutiérrez, km. 12 desvío a
Montebello, 1081ma.s.l., 16° 52′ 20.3″ N, 93° 19′ 32.5″ W,
11 Aug 2016 (fl), M.A.Escobar-Castellanos 0689 (holotype:
HEM!; isotypes: MEXU!, XAL!, MO!).
Description:Trees 3–9m tall and 3–14cm DBH; young
branches slightly covered by light brown or golden-brown
erect and appressed hairs, glabrous with age. Leaves mem-
branaceous to chartaceous, alternate, 11–20 × 4–8 cm,
elliptic to obovate, the apex acute to acuminate, acumen
12–15mm long, the base acute to obtuse, sometimes asym-
metrical; upper surface glabrous, the lower side glabrous;
venation brochidodromus, 6–9 veins per side, pocket doma-
tia in the axils of secondary veins glabrous or nearly so;
the midrib impressed above and slightly canaliculate toward
the base (sometimes with erect to appressed light brown
hairs), lateral veins barely elevated above; the midrib and
lateral veins prominently elevated below and with sparsely
light brown hairs, lateral veins decurrent at midrib inser-
tion; petiole swollen, 5–10mm long, canaliculate, with
sparsely light brown hairs. Inflorescences 1-flowered, axil-
lary, sometimes arising on leafless part of branches (rami-
flory), the pedicel glabrous, 10–17mm long, basal bracts
1–2, minute, broadly ovate, densely covered with golden-
brown hairs. Sepals 2, connate at the base, to 2 × 4–5mm,
decurrent along the pedicel, broadly ovate, rounded at apex,
glabrous inside and outside, the margins ciliate. Petals 4, in
two subequal whorls, 8–14 × 3–5mm, lanceolate to linear-
triangular, green to yellowish green, glabrous inside and
outside, the margins ciliate, acute at apex, the base truncate
and cusped around the stamens; the outer petals, more or
less thin, with faint venation, reflexed at anthesis; the inner
petals thicker and fleshier and not reflexed with a shallow,
more or less triangular white patch near the base. Stamens,
c.a. 40, 1–1.5mm long, extrorse, filament very short, apical
part of connective expanded over the thecae, shield-shaped,
ellipsoid to angulate, glabrous. Carpels, 3–5 per flower, to
2.5mm long; the stigma more or less globose and essen-
tially glabrous; style absent; the ovaries ellipsoid and more
or less curved, with sparsely light brown hairs; the ovules,
12–18, lateral, in two rows. Monocarps, 1–4 per fruit, large
and fleshy, 80–110 × 30–50mm, ellipsoid, the apex and
base rounded, wall smooth or rarely forming longitudinal
folds, glabrous, shortly stipitate, stipes to 7mm long; young
monocarps green, yellow to light brown when ripe with a
peach-like sweet odor. Seeds 10–18, 13–22mm long, lunate
to wedge-shaped, smooth or slightly wart-like dotted, lamel-
late ruminations.
Habitat and distribution: Montane moist forest on limestone
karst soils. The species is endemic to the state of Chiapas in
southern Mexico.
Phenology: The species can be found in full bloom during
the second half of the year from August to October and then
produce fruits during the first months of the year.
Preliminary IUCN conservation assessment: Tridimeris
chiapensis is only known from the type locality and sur-
roundings at the ecological state reserve “La Pera” and the
last collection dates to 2021. The area of occupancy (AOO)
is estimated to 8 km2 and the extent of occurrence (EOO)
is estimated to 8 km2, both within the limits of Critically
Endangered status under criterion B. The species is known
from a single location (sensu IUCN 2022), also within the
limit for Critically Endangered status. All specimens known
so far were collected between 2012 and 2016. Furthermore,
only seven individuals of T. chiapensis were recorded in
one hectare of sampling (Escobar-Castellanos 2016). The
3000ha of La Pera’s rainforest estimated by Espinosa (2014)
are threatened by non-sustainable activities (logging, fires,
illegal settlements). Forests in this region are fragmented
and only some remnants persist, which are surrounded by
roads, croplands and cattle pastures (Medina etal. 2006;
Luna-Reyes etal. 2015). We project that the ongoing loss
of its habitat will induce a strong continuous decline of its
EOO and AOO. This species is thus assigned a preliminary
conservation status of Critically Endangered [CR B1ab (i,
ii, iii) & B2 ab (i, ii, iii)].
Etymology: The specific epithet is name after the Mexican
state of Chiapas where the species occurs.
Notes: Tridimeris chiapensis is the species with the south-
ernmost distribution in the genus. It is the only species that
occurs in Chiapas, Mexico. It is clearly circumscribed within
the Tridimeris sect. Zoque and is phylogenetically related
to T. tuxtlensis and T. uxpanapensis (Fig.1). The three spe-
cies are allopatrically distributed toward southern Mexico
(Fig.7). Tridimeris chiapensis is distinguished from its two
most closely related species by its flowers with more than
two carpels (vs. 3–5), an unusual feature in the entire genus
where most of the species have 1 or rarely 2 carpels per
flower. In addition, its broadly elliptical leaves distinguish it
from T. uxpanapensis, which has narrowly elliptical leaves.
Additional specimens examined: MEXICO, Chiapas,
Zona Sujeta a Protección Ecológica “La Pera,” Predio “La
Selva,” desvío hacia San Joaquín, carretera Berriozábal-
Joaquín Miguel Gutiérrez, Sistema kárstico, 14km al NO
de Berriozábal, 1049ma.s.l., 16°51′ 17″ N, 93°19′ 27″ W,
11 Aug 2016 (fl) M.A.Escobar-Castellanos 0690 (HEM);
Zona Sujeta a Protección Ecológica “La Pera,” Predio “La
Selva,” desvío hacia San Joaquín, carretera Berriozábal-
Joaquín Miguel Gutiérrez, Sistema kárstico, 14km al NO
de Berriozábal, 1050ma.s.l., 16°51′ 25″ N, 93°19′ 32″ W,
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A. E. Ortiz-Rodriguez etal.47 Page 16 of 32
31 Mar 2014 (fr), M.A.Escobar-Castellanos 0556 (HEM);
Zona sujeta a protección ecológica "La Pera," predio "Peña
Flor" camino Berriozábal-Vista Hermosa-El Cairo, km 12
desvío al Pozo Turipache, 1068ma.s.l., 16° 51′ 51″ N, 93°
19′ 52″ W, Mar 2012 (fl), A.E.Ortiz-Rodríguez 178 (MO).
Tridimeris crotalocarpa Ortiz-Rodr., sp. nov.—TYPE:
MEXICO. Oaxaca: Pochutla: municipio de Pluma Hidalgo,
Cerro Espino, al E de la finca cafetalera “Monte Cristo,”
1250ma.s.l., 15° 52′ N, 96° 24′ W, 24 Feb 1988 (fr), Álvaro
Fig. 7 Tridimeris crotalocarpa.
a Fertile twig. b Cylindrical
monocarp with the wall strongly
constricted between the seeds.
Drawn by Robin Pérez Lucas
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 17 of 32 47
Campos Villanueva and Jerónimo Reyes 1491 (holotype:
MEXU!, isotype: MO!). (Fig.7).
Diagnosis: Tridimeris crotalocarpa is distinguished from
other species of Tridimeris by its small leaves less than
10cm long, absence of leaf domatia, narrowly elliptic to del-
toid leaf blades and fruit walls strongly constricted between
seeds when dry.
Description:Trees 8m tall; young branches slightly cov-
ered by light brown or golden-brown erect and appressed
hairs, soon glabrous. Leaves membranaceous, alternate,
6–10.5 × 2–3.5cm, narrowly elliptic to deltoid, the apex
acute to acuminate, acumen 10–15mm long, the base acute
to obtuse, sometimes asymmetrical; upper and lower sur-
face glabrous; venation brochidodromus, 7–8 veins per side,
pocket domatia in the axils of secondary veins absent; the
midrib impressed above and slightly canaliculate toward
the base, glabrous or nearly so, lateral veins barely elevated
above; the midrib and lateral veins prominently elevated
below, glabrous or nearly so, lateral veins decurrent at mid-
rib insertion; petiole swollen, 2–3mm long, canaliculate,
sparsely covered with light brown hairs. Inflorescences one
flowered, axillary, pedicel sparsely covered with light brown
hairs, 4–6mm long, basal bracts 1–2, minute, broadly ovate,
densely covered with brown hairs. Sepals 2, basally con-
nate, 1–2 × 1–2mm, decurrent along the pedicel, broadly
ovate, rounded at apex, glabrous inside, sparsely pubescent
with light brown hairs outside, the margins ciliate. Petals,
stamens and carpels, not seen. Monocarps, 1–3 per fruit,
large and fleshy invivo, ca. 80 × ca. 20mm, ellipsoid, the
apex and base obtuse to rounded, wall strongly constricted
between seeds when dry, glabrous; stipes to 5mm long;
young monocarps green. Seeds 10–16 per monocarp,
15–20mm long, lunate to wedge-shaped, smooth, lamellate
ruminations.
Habitat and distribution: In montane cloud and pine–oak
forests between 1250 and 1890m altitude. The species is
endemic to Oaxaca.
Phenology: Tridimeris crotalocarpa was found in fruit
between February and May. Like other species within the
genus, T. crotalocarpa is likely to be flowering during the
last months of the year.
Preliminary conservation assessment: To date, T. crotalo-
carpa is only known from two specimens collected more
than 30years ago in Sierra Madre del Sur in Oaxaca. The
area of occupancy (AOO) is estimated to 8 km2 within
the limits of Critically Endangered status under criterion
B. Based on these two collections, the species is known
from two locations (sensu IUCN 2022) within the limits
of Endangered status under criterion B. Nevertheless, the
area of distribution of the species appears severally frag-
mented and none of the collections was made in protected
areas. Based on satellite images, the forests appear to be in
a good state, with several expanses of continuous forests
still persisting. We thus expect the species to be present in
the region. Because of a lack of environmental protection in
the region and the ongoing deforestation, we project a con-
tinuous decline in the number of locations and AOO. This
species is thus assigned a preliminary conservation status of
Critically Endangered [CR B2 ab (ii, iii, iv)].
Etymology: The specific epithet of the species refers to its
fruits that resemble the rattle of a snake.
Notes: Tridimeris crotalocarpa is circumscribed within the
Tridimeris sect. Zoque and is phylogenetically related to T.
oaxacana, also present in Oaxaca and the other species with
the fruit wall constricted between the seeds (Fig.1). How-
ever, in T. oaxacana the leaves are broadly elliptic, more
than 10cm long and with pocket domatia in the axils of the
secondary veins. Also, the fruits of T. oaxacana are longer
(up to 130mm long vs 80mm long in T. crotalocarpa) and
with more seeds (up to 27 vs 10–16 in T. crotalocarpa), and
they grow exclusively along the main trunk (vs axillary in
T. crotalocarpa). Moreover, both species are allopatrically
distributed (Fig.7).
Additional specimens examined (paratype): MEXICO.
Oaxaca. Miahuatlán: municipio de San Jerónimo Coatlán,
17.9km al SW de San Jerónimo Coatlán, brecha a Piedra
Larga, 1890ma.s.l., 16° 12′ N, 96° 58′ W, 17 May 1988 (fr),
Álvaro Campos Villanueva 1839 (MEXU).
Tridimeris globosa Ortiz-Rodr., sp. nov. —TYPE: MEX-
ICO. Oaxaca: San Felipe Usila: al SW de Cerro Verde,
1140ma.s.l., 25 May 1991 (fl, fr), J.I. Calzada 16988 and
J. Múgica (holotype: MEXU!; isotype: MO!). (Fig.8).
Diagnosis: Tridimeris globosa is distinguished from other
species of Tridimeris by its leaves less than 10cm long,
setaceous pocket domatia in the axils of the secondary veins;
short (1–3mm long), glabrous pedicels, orbicular petals and
by its globose fruits, with a smooth wall.
Description:Trees 6–8m tall; young branches covered by
light brown or golden-brown erect and appressed hairs, soon
glabrous. Leaves membranaceous, alternate, 5–10 × 2–3cm,
narrowly elliptic, the apex acute to shortly acuminate,
acumen less than 10mm long, the base acute to obtuse,
sometimes asymmetrical; upper and lower surface gla-
brous; venation brochidodromus, 6–8 veins per side, pocket
domatia in the axils of secondary veins, setose; the midrib
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A. E. Ortiz-Rodriguez etal.47 Page 18 of 32
impressed above and slightly canaliculate toward the base,
glabrous, lateral veins barely elevated above; the midrib
and lateral veins prominently elevated below, glabrous or
nearly so, lateral veins decurrent at midrib insertion; peti-
ole swollen, 1–3mm long, canaliculate, glabrous or nearly
so. Inflorescences 1-flowered, axillary, the pedicel glabrous
or very sparsely covered with golden-brown hairs, 1–3mm
long in flower and up to 10mm long in fruit, basal bracts
1–3, minute, sparsely covered with light brown hairs. Sepals
2, basally connate, less than 1mm long, decurrent along
Fig. 8 Tridimeris globosa
Ortiz-Rodr. a Fertile twig with
fruit. b Globose monocarp with
smooth and glabrous surface.
c Longitudinal section of the
fruit; note the thick testa and
the numerous seeds arranged
in two rows. d Flower bud with
two fused sepals which have
ciliated margin. e fertile twig
with leaves. Drawn by Robin
Pérez Lucas
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 19 of 32 47
the pedicel, broadly ovate, rounded at apex, glabrous inside,
glabrous or nearly so outside, the margins ciliate. Petals 4,
in two subequal whorls, 1–2 × 1–2mm, orbicular, sparsely
covered with golden-brown hairs or glabrous inside and
outside, the margins ciliate, rounded at apex, base truncate
and cusped around the stamens. Stamens, and carpels, not
seen. Monocarps 1 per fruit, large and fleshy, 60 × 50mm,
globose, the apex and base obtuse to rounded, wall smooth,
glabrous, shortly stipitate, stipes up to 3mm long. Seeds 9,
lunate to wedge-shaped, 25–30mm long, smooth, lamellate
ruminations.
Habitat and distribution: Montane cloud forest on limestone
karst soils at 1140m altitude. The species is endemic to
Oaxaca.
Phenology: The species is found with fruit in May. In that
same month it has flower buds. It is probable that, as in other
species of the genus, T. globosa has a flowering peak during
the second half of the year (from August to October).
Preliminary conservation assessment: To date, T. globosa
is only known from two specimens collected more than
30years ago at the type locality. The area of occupancy
(AOO) is estimated to be 4 km2, within the limits of Criti-
cally Endangered status under criterion B. The species is
known from a single location (sensu IUCN 2022), also
within the limit of the Critically Endangered status. In addi-
tion, the species is threatened by deforestation and non-sus-
tainable activities (logging, fires, illegal settlements). Forests
in the region are also fragmented and only some remnants
persist. We project that the ongoing loss of its habitat will
induce a strong continuous decline of its AOO. This species
is thus assigned a preliminary conservation status of Criti-
cally Endangered [CR B2 ab (ii, iii)].
Etymology: The specific epithet of the species refers to its
globose fruits.
Notes: The short pedicels in flower (1–3mm long) and fruit
(up to 10mm long), and its leaves with setose pocket doma-
tia in the axil of secondary veins, circumscribe T. globosa
within the T. sect. Tridimeris (Fig.1). Tridimeris globosa
is phylogenetically related to T. hahniana and both species
share leaves of less than 10cm long with setaceous pocket
domatia in the axils of the secondary veins, the glabrous
flower pedicels and the small flowers with orbicular petals.
However, T. globosa differs from its sister species by its
pedicels 1–3mm long (vs 10–20mm long in T. hahniana),
in addition to its allopatric distribution.
Tridimeris hahniana Baill. Adansonia 9: 219. 1869.—
TYPE: MEXICO. Veracruz: Orizaba, Montagne Saint
Christophe, 18.813709° N, -97.134354° W, 1903ma.s.l., 12
August 1865 (fl), L. Hahn s.n. (holotype: P! [P00734865];
isotype: P![P00734864]).(Fig.9).
=Tridimeris baillonii G.E.Schatz, Candollea 49: 466.
1994. nom. superfl.
Description:Trees, young branches slightly covered by
golden-brown erect and appressed hairs, glabrous with
age. Leaves membranaceous to chartaceous, alternate,
5–10 × 2–4cm, elliptic, the apex acute to acuminate, acu-
men less than 10mm long, the base acute to obtuse, rarely
rounded, sometimes asymmetrical; upper surface glabrous,
the lower side glabrous; venation brochidodromous, 6–8
veins per side, pocket domatia in the axils of secondary
veins setaceous; the midrib impressed above and slightly
canaliculate toward the base (sometimes with erect to
appressed light brown hairs), lateral veins barely elevated
above; the midrib and lateral veins prominently elevated
below, sparsely covered with light brown hairs, lateral
veins decurrent at midrib insertion; petiole swollen, 3–5mm
long, canaliculate, sparsely covered with light brown hairs.
Inflorescences 1-flowered, axillary, the pedicel glabrous or
nearly so, 10–20mm long, basal bracts 2–3, minute, densely
covered by golden-brown hairs. Sepals 2, basally connate,
2 × 2–3 mm, decurrent along the pedicel, broadly ovate,
rounded at apex, glabrous inside and outside, the margins
ciliate. Petals 4, in two subequal whorls, 3–4 × 3–4mm,
orbicular, glabrous inside and outside, the margins glabrous,
rounded at apex, base truncate and cusped around the sta-
mens, with faint venation, the outer petals reflexed at anthe-
sis, inner petals rarely with an arc-shaped linear opening at
the base inside. Stamens, ca. 50, 1–1.2mm long, extrorse,
filament very short, apical part of connective expanded over
the thecae, shield-shaped, ellipsoid to angulate, glabrous.
Carpels 1, rarely 2 per flower, 2–3mm long; the stigma
more or less globose, style absent; the ovaries ellipsoid and
more or less curved, densely covered by light brown hairs;
ovules, 8–10, lateral, in two rows. Monocarps and Seeds
not seen.
Habitat and distribution: Montane cloud forest, known only
from the type locality at Cerro San Cristobal in Veracruz,
Mexico, 1904m altitude.
Phenology: The species was found in full bloom in August.
Like other species of the genus, it is expected to have fruits
during the first months of the year.
Preliminary conservation assessment: To date, T. hahni-
ana is only known from one specimen collected more than
150years ago at the type locality. The area of occupancy
(AOO) is estimated to be 4 km2, within the limits of Criti-
cally Endangered status under criterion B. The species is
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A. E. Ortiz-Rodriguez etal.47 Page 20 of 32
known from a single location (sensu IUCN 2022), also
within the limits of the Critically Endangered status under
criterion B. In addition, the forest where this species occurs
is seriously fragmented and threatened by land-use change
such as extraction of stone materials and by the overexploita-
tion of timber resources. It is not possible to assess whether
this species is now extinct, and urgent botanical expeditions
should be planned in the region to confirm its presence. In
the meantime, we project that the ongoing loss of its habitat
will induce a strong continuous decline in its AOO. This
species is thus assigned a preliminary conservation status
of Critically Endangered [CR B2 ab (ii, iii)].
Etymology: The specific epithet honors the German botanist
Ludwig Hahn, who collected the species and genus for the
first time.
Notes: Our analysis of the morphological characteristics
of Ludwig Hahn's collections revealed that the type speci-
men (specimens: Hahn s.n.) and the collections with fruits,
Fig. 9 Tridimeris hahniana.
Type specimen (Hahn s.n.)
deposited at P herbarium
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 21 of 32 47
previously assigned to Uvaria hahniana (specimens: Hahn
239) correspond to two different species. Recent collec-
tions from the center and northern region of Veracruz, and
the states of Puebla, Queretaro and San Luis Potosí, show
almost sessile monocarps with their surface densely cov-
ered by golden-brown hairs, similar to those present in the
collections with fruits of Ludwig Hahn (specimens: Hahn
239). Moreover, these same individuals have leaves more
than 10cm long, with leaf domatia glabrous, flowers almost
sessile, with pedicels, bracts and sepals, densely covered
by golden-brown hairs, all characteristics absent in the type
specimen of T. hahniana (specimens: Hahn s.n.). Our phy-
logenetic analyses support the aforementioned (Fig.1). As
circumscribed here, T. hahniana (specimen: Hahn s.n.) and
Ludwig Hahn's fruiting collections (specimens: Hahn 239)
belong to distinct lineages within the Tridimeris section Tri-
dimeris (Fig.1). Tridimeris hahniana is phylogenetically
related to T. globosa, while Ludwig Hahn's fruiting collec-
tions (described here as T. nebulosa) are phylogenetically
related to T. villosa. Thus, T. hahniana is distinguished from
the other species by its leaves less than 10cm long with
pocket domatia setose, by its globose flowers with orbicular
petals, and with pedicels up to 20mm long.
Tridimeris huatuscoana Marinero-Sobal & Ortiz-Rodr.
Phytotaxa 548 (2): 147, f. 1–3; Table1. 2022.—TYPE:
MEXICO. Veracruz, Huatusco, Río Seco, road between
Ixpila and Huatusco on the way to Tenejapa, approximately
3km south of Huatusco, 1283 m a.s.l., 19.127376° N,
96.981851° W, 2 Jan 2022, E.J. Marinero-Sobal 425 (holo-
type: MEXU!; isotypes: CIB! MO!).
Description:Trees 5–7m tall and 3–14cm DBH; young
branches slightly covered by light brown or golden-brown
erect and appressed hairs, glabrous with age. Leaves mem-
branaceous to chartaceous, alternate, 7–17 × 2.5–5.5cm,
narrowly elliptic to obovate, the apex acute to long acumi-
nate, acumen 10–15mm long, the base acute to obtuse,
sometimes asymmetrical; upper surface glabrous, the lower
side glabrous; venation brochidodromous, 6–9 veins per
side, pocket domatia in the axils of secondary veins setose;
the midrib impressed above and slightly canaliculate
toward the base (sometimes with erect to appressed light
brown hairs), lateral veins barely elevated above; the mid-
rib and lateral veins prominently elevated below and with
sparsely light brown hairs, lateral veins decurrent at mid-
rib insertion; petiole swollen, 3–6mm long, canaliculate,
with sparsely light brown hairs. Inflorescences 2-flowered
short shoots (rhipidia), axillary, flowers develop in succes-
sion, sympodial axis minute, 1–2mm long, densely cov-
ered by golden-brown hairs, flowers almost sessile, pedi-
cels 1–3mm long (up to 5mm in fruit), densely covered
by golden-brown hairs, basal bracts 2–3, minute, broadly
ovate, densely covered by golden-brown hairs. Sepals 2,
basally connate, 2–3 × 2–3mm, decurrent along the pedi-
cel, broadly ovate to orbicular, rounded at apex, glabrous
inside, densely tomentose outside, the margins ciliate. Petals
4, in two subequal whorls, 10–25 × 3–5mm, deltoid, whitish
or beige, rarely yellowish green when immature, glabrous
inside and sparsely to densely pubescent outside, the mar-
gins glabrous, acute to long aristate at apex, base truncate
and cusped around the stamens; outer petals, more or less
thin, with faint venation, reflexed at anthesis; inner petals
thicker, ~ 1mm, fleshier and not reflexed, with a shallow,
more or less triangular white patch near the base inside.
Stamens, 40–45, 1–1.5mm long, extrorse, filament very
short, apical part of connective expanded over the thecae,
shield-shaped, ellipsoid to angulate, glabrous. Carpels 2,
rarely 3 per flower, 2mm long; the stigma more or less
globose and essentially glabrous; style absent; the ovaries
ellipsoid and more or less curved, like a small banana and
densely covered by light brown hairs; the ovules, 10–13,
lateral, in two rows. Monocarps 2, rarely 3 per fruit, large
and fleshy, 50–70 × 30–40mm, ellipsoid to globose, the
apex and base rounded, wall smooth or slightly tuberculate,
glabrous, shortly stipitate, up to 1mm long, or often stipe
absent. Seeds 8–12, lunate to wedge-shaped, 17–20mm
long, smooth, lamellate ruminations.
Habitat and distribution: Montane cloud forest, in riverine
vegetation on limestone karst soils at 1200m altitude. The
species is endemic to the region of Veracruz, Mexico.
Phenology: The species has two flowering peaks, at the end
of the year between October and December, where fruits
can also be observed, and then at the beginning of the year
between March and May, where fruiting is rather absent.
Preliminary conservation assessment: To date, T. huatusco-
ana, is only known from a few collection in the type locality,
with the last collection from 2022. The area of occupancy
(AOO) is estimated to be 4 km2 and a single location (sensu
IUCN 2022), both within the limits of Critically Endangered
status under criterion B. Although this location is within a
large fragment of montane cloud forest it is not protected and
the species appears restricted to the banks of a river where it
is recorded as being rare (less than 10 individuals in one hec-
tare; Ortiz-Rodriguez and Marinero-Sobal 2022). In addi-
tion, the forests around the type locality are threatened by
non-sustainable activities (logging, fires, illegal settlements
and land-use change) and at more local scales the forest is
evidently fragmented characterized by many small isolated
patches which are surrounded by roads, croplands and cat-
tle pastures. We project that the ongoing loss of its habitat
will induce a strong continuous decline in the number of
mature individuals and a decline of its AOO. This species is
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A. E. Ortiz-Rodriguez etal.47 Page 22 of 32
thus assigned a preliminary conservation status of Critically
Endangered [CR B2 ab (ii, iii, v)].
Etymology: The specific epithet is in honor of the municipal-
ity of Huatusco, in Veracruz, Mexico.
Notes: Tridimeris huatuscoana has a set of morphological
characters that clearly distinguish it from any other species
of Tridimeris. Its 2-flowered short inflorescences are unique
within the genus, as are its flowers with long aristate, whit-
ish petals. Its setose leaf domatia, almost sessile flowers and
deltoid petals, circumscribe it within the T. sect. Tridimeris.
It is phylogenetically related to T. globosa and T. hahniana.
The three species form a clade and are the only species in
the genus with setose leaf domatia.
Additional specimens examined. MEXICO. Veracruz: From
the type locality, 4 Sep 2021, E.J. Marinero-Sobal 426,
427,428 (MEXU).
Tridimeris nebulosa Ortiz-Rodr. & Hurtado-Reveles,
nom. nov. for Uvaria hahniana Baill., Adansonia 8: 347.
1867–1868[1868] non Tridimeris hahniana Baill. (1869).—
TYPE: MEXICO. Veracruz, Foret de la montagne Coachil-
ote [Cerro Cojolite]. 4 leagues [16km] from Misantla, 4 Jul
1866 (fr), L. Hahn 239 (holotype: P!) (Fig.10).
Description:Trees 6–30m tall and 1.5–20cm DBH; young
branches slightly covered by light brown or golden-brown
erect and appressed hairs, glabrous with age. Leaves mem-
branaceous to chartaceous, alternate, 6–16 × 2–7cm, elliptic
to obovate, the apex acute to acuminate, acumen 10–17mm
long, the base acute to obtuse, sometimes asymmetrical;
upper surface glabrous, the lower side glabrous; venation
brochidodromous, 7–9 veins per side, pocket domatia in
the axils of secondary veins glabrous; the midrib impressed
above and slightly canaliculate toward the base (sometimes
with erect to appressed light brown hairs), lateral veins
barely elevated above; the midrib and lateral veins promi-
nently elevated below, sparsely covered with light brown
hairs, lateral veins decurrent at midrib insertion; petiole
swollen, 3–5mm long, canaliculate, sparsely covered with
light brown hairs. Inflorescences 1-flowered, axillary, the
pedicel densely covered by golden-brown hairs, 2–5mm
long, basal bracts 2–3, minute, densely covered by golden-
brown hairs. Sepals 2, basally connate, 2 × 2–3mm, decur-
rent along the pedicel, broadly ovate, rounded at apex,
glabrous inside, densely covered by golden-brown hairs
outside, the margins ciliate, persistent in fruit. Petals 4, in
two subequal whorls, 3–7 × 3–4mm, deltoid, green to yel-
lowish green, glabrous inside and sparsely to densely cov-
ered by golden-brown hairs outside, the margins glabrous,
acute at apex, the base concave to geniculate, cusped around
the stamens; all petals, more or less thin, with faint vena-
tion, the outer petals reflexed at anthesis, inner petals rarely
with an arc-shaped linear opening at the base inside. Sta-
mens, ca. 40, 1–1.2mm long, extrorse, filament very short,
apical part of connective expanded over the thecae, shield-
shaped, ellipsoid to angulate, glabrous. Carpels 1, rarely 2
per flower, 2–3mm long; the stigma more or less globose,
style absent; the ovaries ellipsoid and more or less curved,
densely covered by light brown hairs; ovules, 10–16, lat-
eral, in two rows. Monocarps, 1 or 2 per fruit, large and
fleshy, 50–80 × 20–40mm, ellipsoid to globose, the apex
and base rounded, wall wrinkled like a brain or forming
longitudinal folds, densely covered by small golden-brown
hairs (velvety), shortly stipitate, up to 2mm long, or often
stipe absent. Seeds 5–12, lunate to wedge-shaped, 20–22mm
long, smooth, lamellate ruminations.
Habitat and distribution: Montane cloud forest, known from
the Mexican states of Puebla, Querétaro, San Luis Potosi and
Veracruz, from 250 to 900m elevation.
Phenology: The species is found with flowers during the
first months of the year from March to June, when a few
fruits are also observed. The species fruits usually between
August and February when flowers are rarely observed at
the same time.
Preliminary conservation assessment: Tridimeris nebuloa
is known from several collections, with the last ones from
2022. The area of occupancy (AOO) is 16 km2 and the extent
of occurrence (EOO) is 14,130 km2, within the limits of
Endangered and Vulnerable status, respectively, under crite-
rion B. The species occurs along the Sierra Madre Oriental
in eastern Mexico and is known from four locations (sensu
IUCN 2022) within the limits of Endangered status under
criterion B. It has a more or less continuous distribution and
is usually present in well-preserved forests. However, at the
north of its distribution (Queretaro and San Luis Potosi) the
species is threatened by non-sustainable activities (logging,
fires, illegal settlements) and only persists in small forest
fragments. We project that the ongoing loss of its habitat
will induce a strong continuous decline in the number of
locations as well as a continuous decline of its EOO and
AOO. This species is thus assigned a preliminary conserva-
tion status of Endangered [EN B2 ab (i, ii, iii, iv)].
Etymology: The specific epithet refers to its wide and exclu-
sive distribution within the montane cloud forest of eastern
Mexico.
Notes. Tridimeris nebulosa has the northernmost distri-
bution of the genus and is the species with the widest geo-
graphic distribution. Its glabrous leaf domatia; almost sessile
flowers, deltoid petals with the base concave to geniculate
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 23 of 32 47
and cusped around the stamens; and its monocarps with
velvety surface, distinguish T. nebulosa from any other spe-
cies. Tridimeris nebulosa is phylogenetically related to T.
villosa, the other species in the genus with velvety fruit sur-
face. However, in T. villosa the leaves and twigs are densely
covered by brown hairs (vs glabrous in T. nebulosa) in addi-
tion to having more secondary veins per side (14–17), larger
leaves (10–20cm) and more seed per fruit (16–30).
Some individuals from Puebla (MEXU: Sarukhán et al.
4495, F. Salazar sn) have atypically long acuminate young
Fig. 10 Tridimeris nebulosa. a
Fertile twig. b Almost sessile
flower, side view. c Dimerous
flower; note the reduced num-
ber of carpels. d Cylindrical
monocarps with smooth surface
densely covered by short hairs
(velvety). E Young mono-
carps. f Abaxial leaf surface;
note the pocket domatia in the
axils of the secondary veins.
g Monocarp cross section;
note the lamellate ruminations
of the seeds. Photographs by
Canek Ledesma Corral, Osbel
López and Anastasio Sotero
Hernández (a, c), Leopoldo
Hurtado Reveles (b, d, e, f), and
Ceferino Salgado (G)
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A. E. Ortiz-Rodriguez etal.47 Page 24 of 32
leaves (acumen 20–30mm long), but they conform to the
concept of T.nebulosa in terms of their other leaf, flower
and fruit characteristics.
Additional specimens examined (paratypes): MEXICO.
Puebla: Agua Dulce, 4km al SE de Ahuacatlan, brecha a
Zapotitlan, Mpio. Ahuacatlan. 1180ma.s.l., 20° 01′ N, 97°
50′ W, 27 Feb 1987 (fr), G. Toriz A. et al. 313 (MEXU);
Agua Fria (Mpio. Venustiano Carranza), en el kilómetro 3.4
del camino que va de la granja “El Peñon” a Agua Fria, 16
Jun 1962 (st), Sarukhán et al. 4495 (MEXU); Zongozotla,
camino real Zongozotla-Totutla, por la localidad Canax-
Kiwi, 1295ma.s.l., 19.95346° N, -97.73082 W, 20 May
2016 (fr), Canek Ledesma Corral et al. 21925 (MEXU);
Huauchinango, Apr 1914 (fr), F. Salazar s.n. (MEXU).
Querétaro: Mpio. de Landa de Matamoros, 5km al S de El
Húmo, por la brecha a Neblinas, 1100ma.s.l., 21° 16′ 35″
N, 99° 05′ 33″ W, 29 Jun 2010 (fr), S. Zamudio et al. 14778
(MEXU, IEB); Mpio. de Landa de Matamoros, El Banco,
1.5km al poniente de El Puerto Hondo, 1800 m a.s.l.,
29 Nov 1995 (fr), P. Tenorio and L. Hiram Rubio 19203
(MEXU, IEB). San Luis Potosí: Entre Taman y San Fran-
cisco, Municipio de Tamazunchale, 600–900m a.s.l., 29 Jun
1959 (fl), Rzedowski 11033 (WIS); Xilitla, camino a Cru-
citas, 647m a.s.l., 21.414897° N, -98.978736° W, 25Mar
2022 (fl, fr), L. Hurtado 717 (MEXU). Veracruz: Cerro
La Espaldilla, 5km N of Misantla, 250–350m a.s.l., 19°
58′ N, 96° 50′ W, 14 Jun 1986 (fl, fr), G.E. Schatz et al.
1198 (MEXU, WIS); 29 Mar 1986 (fr), Cerro La Espaldi-
lla, 5km N of Misantla, 250–350m a.s.l., 19° 58′ N, 96°
50′ W, Martínez Pérez and Martínez Pérez 1191 (XAL);
5km del límite Puebla Veracruz, carretera Teziutlan-Tlapa-
coyan, 900m a.s.l., 13 Jul 1971 (fr), Nevling and Chang
1637 (WIS), Huatusco, Río seco, road between Ixpila and
Huatusco on the way to Tenejapa, 1283m a.s.l.,19.127376°
N, 96.981851° W, 20Mar 2022 (fl,fr), E. Marinero and J.J
Vega 428 (MEXU).
Tridimeris villosa Ortiz-Rodr., sp. nov.—TYPE: MEX-
ICO. Oaxaca, San Felipe Usila, Nueva Santa Flora, 700m
a.s.l., 17° 54′ 99″ N, -96° 26′ 99″ W, 20 December 1992
(fr), Guillermo Ibarra Manríquez et al. 3779 (holotype:
MEXU!). (Fig.11).
Diagnosis: The twigs and leaves densely covered with yel-
lowish or brown hairs and its velvety fruits, clearly separate
T. villosa from any other species within the genus Tridimeris.
Description:Trees 7–14m tall and 15 cm DBH; young
branches sparsely to densely covered by erect, light brown
to reddish hairs, hairs persistent with age. Leaves membrana-
ceous to chartaceous, alternate, 10–20 × 4–7cm, elliptic to
obovate, the apex long acuminate, acumen 15–35mm long,
the base obtuse to rounded, sometimes asymmetrical; upper
surface sparsely to densely covered by erect to appressed
light brown hairs, the lower side densely covered by erect
to appressed light brown hairs, hairs clearly discernible to
the naked eye and to the touch; venation brochidodromous,
14–17 veins per side, pocket domatia in the axils of second-
ary veins glabrous inside but hidden by leaf pubescence; the
midrib impressed above and slightly canaliculate toward the
base (with erect to appressed light brown hairs), lateral veins
barely elevated above; the midrib and lateral veins promi-
nently elevated below and with densely light brown hairs,
lateral veins decurrent at midrib insertion; petiole swollen,
3–5mm long, canaliculate, densely covered by light brown
hairs. Inflorescences 1-flowered, axillary, pedicels 7–10mm
long in fruit, sparsely covered by light brown hairs, basal
bracts 1–3, minute, densely covered by light brown hairs.
Sepals 2, basally connate, 2mm long in fruit (persistent),
decurrent along the pedicel, broadly ovate, obtuse at apex,
glabrous inside, densely covered by light brown hairs
outside, the margins ciliate. Petals, stamens and carpels,
not seen. Monocarps, 1 or 2 per fruit, large and fleshy,
50–100 × 30mm, cylindrical and more or less curved, the
apex and base obtuse to rounded, wall smooth or with faintly
visible longitudinal folds, densely covered by small golden-
brown hairs (velvety), shortly stipitate, up to 5mm long, or
often stipe absent. Seeds 16–30, lunate to wedge-shaped,
20–23mm long, smooth, lamellate ruminations.
Habitat and distribution: Tropical rain forest between 600–
700m altitude. The species is endemic to Oaxaca, Mexico.
Phenology: The species was found with fruits toward the end
of the year (September to December). Like other species in
the genus, it is likely that the species has flowers between
August and September and then between March and May.
Preliminary conservation assessment: To date, T. villosa
is only known from two specimens collected from the type
locality more than 30years ago. The area of occupancy
(AOO) of T. villosa is 4 km2, within the limits of Critically
Endangered status under criterion B. The species is known
from a single location (sensu IUCN 2022), also within the
limit for Critically Endangered status. In addition, the for-
ests where this species is distributed are seriously threatened
by non-sustainable activities (logging, fires, illegal settle-
ments) and forests in this region are fragmented and only
some remnants persist. We project that the ongoing loss of
its habitat will induce a strong continuous decline of mature
individual and AOO. This species is thus assigned a pre-
liminary conservation status of Critically Endangered [CR
B2 ab (ii, iii,v)].
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 25 of 32 47
Etymology: The epithet refers to its persistent hairs on twigs,
leaves and fruits, a characteristic that easily distinguishes it
from any other species in the genus.
Notes. Tridimeris villosa is clearly circumscribed within the
T. sect. Tridimeris, being phylogenetically related to T. nebu-
losa. Both species share the velvety fruit surface, and they
are the only two species in the genus with this type of fruit.
The twigs and leaves densely covered with light brown hairs,
easily distinguishes T. villosa from its relatives and from any
other species within the genus, since it is the only species
with pubescent leaves known so far.
Additional specimens examined (paratypes). MEXICO.
Oaxaca: San Felipe Usila, alrededores del poblado Nueva
Santa Flora 11km en línea recta al NNE de San Felipe Usila,
600m a.s.l., 17° 54′ 99″ N, -96° 26′ 99″ W, 26 Sep 1992,
Guillermo Ibarra Manríquez 3779 (MEXU).
Fig. 11 Tridimeris villosa. a
Fertile twig. b Rounded leaf
base. c Cylindrical monocarp
with smooth surface densely
covered by short hairs (velvety).
d Seeds. Drawn by Robin Pérez
Lucas
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A. E. Ortiz-Rodriguez etal.47 Page 26 of 32
Tridimeris cauliflora G.E.Schatz, sp. nov.—TYPE: MEX-
ICO. Oaxaca: Distrito Ixtlan, Municipio de Ixtlán, Rio Soy-
alapan watershed, E side of river, N side of ridge just above
mostly abandoned settlement of Ladu, 17° 37′ N, 96° 17′
W, 765–805m a.s.l., 20 Nov 1994 (fr), B. Boyle, A. Boyle
and A. Montes 3879 (holotype: MO!; isotype: MEXU!).
(Fig.12).
Diagnosis: Tridimeris cauliflora is the only species with
cauliflorous inflorescences, its leaves with leaf domatia gla-
brous or nearly so, long monocarps (up to 135mm long),
with numerous seeds (14–30) and the wall slightly con-
stricted between seeds, distinguish it from any other species.
Description:Trees 8–15m tall and 11–15cm DBH; young
branches sparsely covered with light brown or golden-
brown erect and appressed hairs, becoming glabrous
with age. Leaves membranaceous to chartaceous, alter-
nate, 7–17 × 2.5–7cm, elliptic to obovate, the apex acute
to acuminate, acumen 10–15mm long, the base acute to
obtuse, sometimes asymmetrical; upper surface glabrous,
the lower side glabrous; venation brochidodromus, 8–10
Fig. 12 Tridimeris cauliflora.
a Fertile twig. b Cylindri-
cal monocarp with the wall
constricted between the seeds.
Drawn by Robin Pérez Lucas
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 27 of 32 47
veins per side, pocket domatia in the axils of secondary veins
glabrous or with a few hairs around the mouth; the midrib
impressed above and slightly canaliculate toward the base,
sparsely covered with erect to appressed light brown hairs to
glabrous, lateral veins slightly raised above; the midrib and
lateral veins prominently raised below, sparsely covered with
light brown hairs, lateral veins decurrent at midrib inser-
tion; petiole swollen, 3–5mm long, canaliculate, sparsely
covered with light brown hairs. Inflorescences 1-flowered,
cauliflorous, arising from the main trunk, at a distance of
approximately 1m above the base; flowering pedicel gla-
brous, 20–25mm long, basal bracts 1–2, minute, broadly
ovate, densely covered with light brown hairs. Sepals 2,
basally connate, not persistent and then only as scars where
observed. Petals, stamens and carpels not seen. Monocarps
1–2, 40–135 × 25–30mm, ellipsoid to narrowly oblong, the
apex and base rounded, wall slightly constricted between
seeds, fleshy invivo, glabrous; stipes to 7mm long. Seeds
14–30 per monocarp, lunate to wedge-shaped, 20–23mm
long, smooth, lamellate ruminations.
Habitat and distribution: Montane cloud forest between
700–1200m. The species is endemic to Oaxaca, Mexico.
Phenology: Fruiting material collected on November and
December. It is likely that the species has flowers between
March to July, like other species in the genus.
Preliminary conservation assessment: To date; T. cauliflora
is only known from three specimens collected more than
30years ago around the type locality. The area of occu-
pancy (AOO) is estimated to be 4 km2, within the limits of
Critically Endangered status under criterion B. The species
is known from a single location (sensu IUCN 2022), also
within the limit for Critically Endangered status. Moreover,
the forests where this species is distributed are seriously
threatened by non-sustainable activities (logging, fires, ille-
gal settlements) and forests in this region are fragmented
and only some remnants persist. We project that the ongoing
loss of its habitat will induce a strong continuous decline of
mature individual and AOO. This species is thus assigned
a preliminary conservation status of Critically Endangered
[CR B2 ab (ii, iii,v)].
Etymology: The specific epithet refers to its cauliflorous
inflorescences.
Notes. Tridimeris cauliflora is distinguished by its cauli-
florous inflorescences, unique in the genus, its cylindrical,
elongated fruits, with the wall constricted between the seeds,
and by its leaves with glabrous pocket domatia in the axils of
the secondary veins. The species is circumscribed within T.
sect. Zoque, it is phylogenetically related to T. crotalocarpa
(Fig.1). See under that species for differences.
Additional specimens examined (paratypes): MEXICO.
Oaxaca: Municipio de Ixtlán. Río Soyolapan watershed, E
side of river. N slope of ridge just above mostly abandoned
settlement of Ladú. Humid premontane forest, with large
trees and lianas; little moss on trunks, relatively few epi-
phytes, 17° 37′ N, 96° 17′ W, 765–805m a.s.l., 20 Nov 1994
(fr), B. Boyle, A. Boyle and A. Montes 3912 (MO); Camino
Tiltepec a la Luz, 17° 30′ 35″ N, 96° 20′ 02″ W, 1130m
a.s.l., 3 Dec 1999 (fr), Jaime Rivera H., Sánchez García, I.
& Juan Carlos Flores V. 2059 (MO).
Tridimeris tuxtlensis G.E.Schatz sp. nov.—TYPE: MEX-
ICO. Veracruz: San Andrés Tuxtla, Estación de Biología
Tropical Los Tuxtlas, Jardín Botánico, 10 Aug 1982 (fl), G.
Ibarra 235 (holotype: MEXU!; isotype: XAL!). (Fig.13).
Diagnosis: Tridimeris tuxtlensis is similar to T. chiapensis
in its vegetative characters, but differs from it by its flowers
with one rarely two carpels, its petals obtuse or rounded at
the tip, and by its globose pollen grains with strongly rugu-
late to fossulate ornamentation.
Description:Trees 8–25m tall and 11–15cm DBH; young
branches slightly covered with appressed, golden-brown
hairs, becoming glabrous with age. Leaves membranaceous
to chartaceous, alternate, 11–22 × 4–8cm, elliptic to obo-
vate, the apex acute to acuminate, acumen 8–10mm long,
the base acute to obtuse, sometimes asymmetrical; upper
surface glabrous, the lower side glabrescent; venation bro-
chidodromus, 6–8 veins per side, pocket domatia in the axils
of secondary veins glabrous; the midrib impressed above and
slightly canaliculate toward the base, sparsely covered with
erect to appressed light brown hairs, lateral veins slightly
raised above; the midrib and lateral veins prominently raised
below, sparsely covered with light brown hairs, lateral veins
decurrent at midrib insertion; petiole swollen, 5–10mm
long, canaliculate, sparsely covered with light brown hairs.
Inflorescences 1-flowered, axillary, flowering pedicel,
10–15mm long, glabrous or nearly so, basal bracts 1–2,
minute, broadly ovate, densely covered with light brown
hairs. Sepals 2, basally connate, ca. 2 × 3–4mm, decurrent
along the pedicel, broadly ovate, rounded at apex, glabrous
inside and outside, the margins ciliate. Petals 4, in two sub-
equal whorls, 5–14 × 3–4mm, lanceolate to linear-triangular,
yellowish green to cream yellow invivo, obtuse to rounded
at apex, the base truncate and cusped around the stamens,
glabrous inside and outside, the margins ciliate; outer petals,
more or less thin, with faint venation, reflexed at anthesis;
the inner petals thicker and fleshier and not reflexed with a
shallow, more or less triangular white patch/opening near the
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A. E. Ortiz-Rodriguez etal.47 Page 28 of 32
base. Stamens, ca. 40, about 1mm long, extrorse, filament
very short, apical part of connective expanded over the the-
cae, shield-shaped, ellipsoid to angulate, glabrous. Carpels
1–2 per flower, to 2mm long; the stigma more or less glo-
bose, glabrous; style absent; the ovaries ellipsoid and more
or less curved, sparsely covered with light brown hairs; the
ovules, 10–19, lateral, in two rows. Monocarps 1–2 per fruit,
80–100 × 25–30mm, ellipsoid, the apex and base rounded,
wall smooth or rarely forming longitudinal folds, large and
fleshy, glabrous, stipes to 5mm long; young monocarps
green, yellow to light brown when ripe with a banana-like
sweet scent. Seeds 10–16 per monocarp, lunate to wedge-
shaped, 1.5–2.5cm long, smooth, lamellate ruminations.
Habitat and distribution: Tropical rainforest between 100–
400m. The species is endemic to Veracruz, Mexico. Known
only from the Los Tuxtlas region, from Estación Biológica
Los Tuxtlas, and nearby Volcan San Martín.
Phenology: The species is in full bloom between March to
June, when some fruits can be observed. Fruiting specimens
were found toward the end of the year.
Preliminary IUCN Conservation status: Tridimeris tuxtlen-
sis is known from several collections, with the last collec-
tion from 2005. The area of occupancy (AOO) is estimated
to 12 km2 and the extent of occurrence (EOO) is estimated
to 13 km2, within the lower estimate for Endangered and
well within the Critically Endangered status, respectively,
under criterion B. The species is known from a single loca-
tion (sensu IUCN 2022, all collections within a protected
area) within the limits of Endangered status. To date, all
collections of this species were made within the protected
natural area Los Tuxtlas Biosphere Reserve of the UNE-
SCO. The species, however, appears to be scarce (less
than 10 individuals in one hectare; Guillermo Ibarra, pers.
comm.). The forests around the reserve are threatened by
non-sustainable activities (logging, fires, illegal settlements
and land-use change) and at more local scales the forest is
evidently fragmented characterized by many small, isolated
patches which are surrounded by roads, croplands and cattle
pastures. Given its presence within Los Tuxtlas Biosphere
Reserve we cannot infer a continuous decline of its popu-
lations. However, given it has a very small and restricted
population with an AOO of less than 20km2, we assign a
Fig. 13 Tridimeris tuxtlensis. a Herbarium specimen in fruit (R. Cedillo 3017) deposited at MEXU herbarium. b Flower close-up. c Fertile twig;
note the flower buds and a flower in anthesis. Photographs by C. Davidson, available at https:// flora ofthe world. org/
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Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 29 of 32 47
preliminary conservation status of Vulnerable under crite-
rion D [VU D2].
Etymology: The specific epithet is in honor of the Los Tuxt-
las region, in Veracruz, Mexico.
Notes: The vegetative characteristics of T. tuxtlensis are rem-
iniscent of those of T. chiapensis, mainly in the size of the
leaves, absence of pubescence and in the glabrous domatia.
However, when fertile, T. tuxtlensis differs from T. chiapen-
sis in several ways. 1) T. tuxtlensis has one rarely two carpels
per flower (vs 2–5 in T. chiapensis); 2) T. tuxtlensis has pet-
als obtuse or rounded at the tip (vs acute in T. chiapensis);
3) Pollen grains of T. tuxtlensis are globose with strongly
rugulate to fossulate ornamentation (vs elliptic with weakly
rugulate to fossulate ornamentation in T. chiapensis); 4) both
species are allopatrically distributed and separated by more
than 260km with no known intermediate localities.
Additional specimens examined. MEXICO. Veracruz:
Municipio San Andres Tuxtla, around Estacion Biologica
Los Tuxtlas, 18° 35′ N, 95° 04′ W, 100–400m a.s.l., 10 Mar
1982 (fr), G.E. Schatz and G. Ibarra 1128 (MEXU, WIS);
12 Jun 1986 (fl), Schatz and Alverson 1192 (WIS); 29 Jan
1983 (fr), Torres et al. 2105 (MEXU); 25 May 2001 (fr), A.
Rincón G. and C.M. Durán-Espinosa, J. Smith, C. Davidson
and H. Velasco 2419 (XAL); 9 Feb 1985 (fr), R. Cedillo
3017 (MEXU); Mar 1983 (fl, fr), G. Ibarra 464 (MEXU);
14 Apr 2005 (fr), E. Velasco-Sinaca 658 (MEXU).
Tridimeris uxpanapensis G.E. Schatz sp. nov.—TYPE:
MEXICO. Oaxaca: Zona Uxpanapa, Municipio Santa Maria
Chimalapa, hills to N and E of Arroyo Chocolin, Congreg-
acion de Nicolds Bravo, to N and E of Rancho Rutt, ca.
3–5km to S of settlement of Rio Alegre, 17.174911° N,
-94.699984 W, 250m a.s.l., 17 Apr 1984 (fr), Schatz and
T. Wendt 990 (holotype: MO!; isotype: MEXU!). (Fig.14).
Diagnosis: Similar to T. chiapensis in its glabrous leaves,
fruits and pocket domatia, but differs from it by its nar-
rowly elliptical leaves, its flowers with one carpel, and by
its smaller monocarps.
Trees 2–3m tall; young branches slightly covered with
appressed and golden-brown hairs, glabrous with the age.
Leaves membranaceous, alternate, 8–17 × 2–5cm, nar-
rowly elliptic, the apex acute to long acuminate, acumen
10–20mm long, the base acute to attenuate, sometimes
asymmetrical; upper surface glabrous, the lower side gla-
brous or nearly so; venation brochidodromus, 8–10 veins
per side, pocket domatia in the axils of secondary veins gla-
brous; the midrib impressed above and slightly canaliculate
toward the base, sparsely covered with erect to appressed
light brown hairs or glabrous, lateral veins barely elevated
above; the midrib and lateral veins prominently elevated
below, sparsely covered with light brown hairs, lateral
veins decurrent at midrib insertion; petiole swollen, 3–5mm
long, canaliculate, sparsely covered with light brown hairs.
Inflorescences 1-flowered, axillary, the pedicel glabrous,
8mm long (up to 11mm in fruit), basal bracts 1–2, minute,
broadly ovate, densely covered with golden-brown hairs.
Sepals, petals, stamens and carpels, not seen. Monocarps,
1 per fruit, large and fleshy, 40 × 25mm, ellipsoid, the apex
and base rounded, wall smooth or rarely forming longitudi-
nal folds, glabrous, shortly stipitate, stipe 3mm long. Seeds
8, lunate to wedge-shaped, 18–20cm long, smooth, lamel-
late ruminations.
Habitat and distribution: Tropical rainforest, 250m altitude.
The species is endemic to the Uxpanapan region in Veracruz
and Oaxaca, Mexico.
Phenology: Fruiting specimens were found in April.
Preliminary conservation status: To date; T. uxpanapensis is
only known from three specimens, two collected more than
30years ago and the other more recently in 2019. The area
of occupancy (AOO) is estimated to 8 km2, within the limits
of the Critically Endangered status under criterion B. The
species is known from two locations (sensu IUCN 2022),
also within the limit of the Endangered status. However,
the species is severally fragmented. In addition, the forests
where this species is distributed are seriously threatened by
non-sustainable activities (logging, fires, illegal settlements)
and forests in this region are fragmented and only some rem-
nants persist. We project that the ongoing loss of its habitat
will induce a strong continuous decline in the number of
locations as well as a decline of its AOO, and mature indi-
viduals. This species is thus assigned a preliminary conser-
vation status of Critically Endangered [CR B2 ab (ii, iii,v)].
Etymology: The specific epithet is in honor of the Uxpanapa
region, in Veracruz and Oaxaca, Mexico.
Notes. Tridimeris uxpanapensis is clearly circumscribed
within the T. sect. Zoque and is phylogenetic related to T.
chiapensis and T. tuxtlensis (Fig.1). Its narrowly elliptical
to lanceolate leaves distinguish it very well from the other
two species in the absence of flowers or fruits. Its small
fruits, less than 50mm long, contrast with the large fruits
(80–100mm long) of the other two species. Tridimeris
uxpanapensis is so far the only species of the genus present
in the Uxpanapa area.
Additional specimens examined. MEXICO. Veracruz: Zona
de Uxpanapa (Poblado 6), entre Plan de Arroyo y hermanos
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

A. E. Ortiz-Rodriguez etal.47 Page 30 of 32
Cedillo, 17.290214 N, -94.601848 W, 115m a.s.l., Apr 2019
(st), Karina Lagos Báez 16 (MEXU).
Information onElectronic Supplementary Mate-
rial
Online Resource 1. ASTRAL species tree based on 290 Annonaceae
wide exons.
Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s00606- 024- 01929-8.
Acknowledgements We extend our sincere gratitude to Robin Pérez
Lucas for the wonderful botanical illustrations and Berenit Mendoza-
Garfias at the Laboratory of Electron Microscopy and Photography,
Instituto de Biología of Universidad Nacional Autónoma de México
(IBUNAM) for the SEM pictures. We especially thank the curators
Fig. 14 Tridimeris uxpanap-
ensis. Type specimen (Schatz
and T. Wendt 990) deposited at
MEXU herbarium. Drawn by
Robin Pérez Lucas
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

Taxonomy, systematics and conservation of the highly threatened and endemic Mexican genus
Page 31 of 32 47
and staff of the visited herbaria (HEM, IEB, MEXU, MO, OAX, P
and XAL).
Author contributions AEOR conceived the idea, wrote the main manu-
script text, analyzed the data and conducted the taxonomic review, FN
and VS generated the genetic data and conducted the bioinformatic
analyses, CR reviewed herbarium specimens and the conservation sta-
tus of the species, GES reviewed herbarium specimens and described
species, MFMV performed the phylogenetic analyses, LHR described
species and prepared figures, MRO reviewed herbarium specimens,
and TLPC conceived the idea, conducted the phylogenetic analyses,
and reviewed herbarium specimens and the conservation status of the
species. All authors reviewed the manuscript.
Funding This project has received funding from the European
Research Council (ERC) under the European Union’s Horizon 2020
research and innovation program (Grant Agreement No. 865787) to
TLPC
Declarations
Competing interests The authors declare no competing interests.
Open Access This article is licensed under a Creative Commons Attri-
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permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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