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Is Rhizoplaca (Lecanorales, lichenized
Ascomycota) a monophyletic genus?
U. Arup and M. Grube
Abstract:Rhizoplaca Zopf is a genus characterized by an umbilicate thallus with an upper and a lower cortex, as well
as a cupulate hypothecium. It has been considered to be related to Lecanora Ach., the type genus of the Lecanoraceae
and, in particular, to the lobate species of this genus. The phylogeny of Rhizoplaca, the monotypic Arctopeltis thuleana
Poelt, and a number of representatives of different groups of Lecanora is studied, using sequences from the nuclear ri-
bosomal internal transcribed spacer (ITS) regions. The results suggest an origin for Rhizoplaca species within the large
genus Lecanora. A well-supported monophyletic assemblage includes the umbilicate type species Rhizoplaca
melanophthalma (DC.) Leuck. & Poelt, the lobate Lecanora novomexicana H. Magn., and five vagrant Rhizoplaca spe-
cies. Rhizoplaca chrysoleuca (Sm.) Zopf and Rhizoplaca subdicrepans (Nyl.) R. Sant. form a separate well-supported
group and Rhizoplaca peltata (Ram.) Leuck. & Poelt is more closely related to Lecanora muralis (Schreb.) Rabenh.
Together with data on secondary chemistry, the results show that the umbilicate thallus with a lower and an upper cor-
tex, as well as apothecia with a cupulate hypothecium found in Rhizoplaca and A. thuleana, have developed several
times in independant lineages in Lecanora. The thallus morphology in lecanoroid lichens is highly variable and does
not necessarily reflect phylogenetic relationships.
Key words:Rhizoplaca,Lecanora, Lecanorales, phylogeny, ITS.
Résumé : Le genre Rhizoplaca Zopf est caractérisé par un thalle ombiliqué muni de cortex supérieur et inférieur, ainsi
que d’ un hypothèce cupulé. On a considéré qu’il serait relié au Lecanora Ach., le genre type des Lecanoraceae, et
particulièrement aux espèces lobées de ce genre. En utilisant les séquences des régions de l’espaceur ribosomal nu-
cléaire interne transcrit (ITS), les auteurs ont étudié la phylogénie des Rhizoplaca,del’Arctopeltis thuleana Poelt mo-
notypique, et d’un nombre de représentants de différents groupes de Lecanora. Les résultats suggèrent une origine pour
les espèces de Rhizoplaca à l’intérieur du genre Lecanora étendu. Un regroupement monophylétique bien supporté in-
clut: l’espèce type ombiliquée Rhizoplaca melanophthalma (DC.) Leuck. & Poelt, l’espèce lobée Lecanora novomexi-
cana H. Magn., et cinq espèces mal définies de Lecanora.LeRhizoplaca chrysoleuca (Sm.) Zopf et le Rhizoplaca
subdicrepans (Nyl.) R. Sant. forment un groupe séparé, bien supporté, et le Rhizoplaca peltata (Ram.) Leuck & Poelt
est plus étroitement apparenté au groupe Lecanora muralis (Schreb.) Rabenh. Pris ensemble avec les résultats de la
chimie secondaire, les résultats montrent que le thalle ombiliqué muni de cortex inférieur et supérieur, ainsi que
d’apothèce avec hypothèce cupulé qu’on retrouve chez les Rhizoplaca et l’ A. thuleana, se sont développés plusieurs
fois dans des lignées indépendantes chez les Lecanora. La morphologie du thalle, chez les lichens lecanoroïdes, est très
variable et ne reflète pas nécessairement les relations phylogénétiques.
Mots clés :Rhizoplaca, Lecanora, Lecanorales, phylogénie, ITS.
[Traduit par la Rédaction] Arup and Grube 327
Introduction
Thallus morphology has traditionally been used in lichen
systematics to distinguish taxa at different levels. For exam-
ple, the family Caloplacaceae, with crustose members, was
distinguished from the family Teloschistaceae, which includes
foliose to fruticose lichens (Zahlbruckner 1926). Within the
latter, the genus Xanthoria (Fr.) Th. Fr. was separated from
the genus Teloschistes Norman mainly by a foliose thallus
with rhizines versus a fruticose thallus. Another case is the
separation of the crustose Buelliaceae from the foliose to
fruticose Physciaceae; analogous examples are also found
within the large family Lecanoraceae. Lobate species of Le-
canora Ach. have primarily been treated as subgenus Placo-
dium, and the two genera Arctopeltis Poelt (Poelt 1983) and
Rhizoplaca Zopf (Leuckert et al. 1977) have been separated
from the genus Lecanora mainly by their umbilicate thalli
with well-developed upper and lower cortices.
While this classification scheme works well for many spe-
cies, those with intermediate thallus characters are difficult
to classify using traditional generic concepts. During the last
decade, ascomatal characters have become more and more
important in the classification of families (e.g., Hafellner
1984) and genera (e.g., Thell and Goward 1996). However,
there is sometimes little variation of these characters within
a family or between genera and no further support for genera
that are characterized mainly by thallus morphology. In such
Can. J. Bot. 78: 318–327 (2000) © 2000 NRC Canada
318
Received January 18, 1999.
U. Arup. Department of Systematic Botany, University of
Lund, Östra Vallgatan 14-20, SE-223 61 Lund, Sweden.
M. Grube.1Institut für Botanik, Karl-Franzens-Universität
Graz, Holteigasse 6, A-8010 Graz, Austria.
1Author to whom all correspondence should be addressed
(e-mail: martin.grube@kfunigraz.ac.at).
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cases, molecular data offer alternatives for evaluating pro-
posed taxonomy.
The genus Rhizoplaca comprises saxicolous species con-
taining usnic acid that are more or less umbilicate and fixed
to the substrate or fruticose and free-living as vagrant li-
chens (Ryan and Nash 1997). Originally, this genus was seg-
regated from the genus Squamaria DC. (now Squamarina
Poelt) by Zopf (1905) on the basis of a single central strong
rhizoid that attaches the lichen to the substrate. Vagrant spe-
cies without this rhizoid were later included (Ryan and Nash
1997). The genus was also recognized by Choisy (1929),
who described it under the later synonym Omphalodina M.
Choisy. Choisy (1929) used the umbilicate thallus morphol-
ogy and the occurrence of two algal layers in the apothecium
to characterize the genus. However, the latter characteristic
was subsequently found to be atypical for the genus
(Leuckert et al. 1977).
Poelt (1958) adopted a very wide circumscription of the
genus Lecanora and included the genus Rhizoplaca as sec-
tion Omphalodina in the subgenus Placodium. Almost
20 years later, Leuckert et al. (1977) once again raised the
group to generic level, using the oldest name available, Rhi-
zoplaca. The authors’ arguments for this treatment were that
the genus is homogeneous in morphology, ecology, distribu-
tion, and chemistry, and that no intermediate forms occur be-
tween Rhizoplaca and other groups within Lecanora, at least
not within the “Lecanora subfusca” group (= the Lecanora
allophana group in a wider sense), which includes the type
species of the genus, L. allophana.Rhizoplaca could, ac-
cording to the authors, be distinguished by the umbilicate
growth form, distinct upper cortex, rather loose medulla, and
thick lower cortex. Since then, the status of the genus has
not been questioned, but Ryan and Nash (1997) have pointed
out that the boundaries between Lecanora and Rhizoplaca
need further clarification. However, because of the cupulate
structure of the apothecia, it has even been proposed that the
genus belongs to another family, the Parmeliaceae (Lumbsch
et al. 1991), which can be characterized by a cupula struc-
ture in the ascomata, besides differences in pycnidial charac-
ters. This view was rejected by Roux et al. (1993), who
showed that the pseudoparenchymatic cupula in the Parmel-
iaceae is different from superficially similar structures in
Lecanora.
It is likely that thallus characteristics have evolved in par-
allel in lichen-forming ascomycetes, as has been shown for
“cladoniiform” lichens by Stenroos and DePriest (1998).
Also, phylogenetic studies on Lecanora subgenus Placodium
using DNA sequence data from the internal transcribed
spacer (ITS) regions of nuclear ribosomal DNA, indicated
that growth forms may vary considerably within some spe-
cies and groups of Lecanora (Arup and Grube 1998). Be-
cause these results already affect the traditional infrageneric
classification of Lecanora, we were interested in re-
investigating the generic boundaries between Lecanora and
Rhizoplaca and in re-evaluating the role of morphological
characters in generic delimitation.
Materials and methods
Lichen material for this study was borrowed from the herbaria
of Arizona State University (ASU), University of Copenhagen (C),
and Karl-Franzens-Universität Graz (GZU), and from the private
herbaria of U. Arup and H.R. Rosentreter. The growth form and
collection sites of the species or specimens studied are listed in Ta-
ble 1.
Total DNA was extracted from individual thalli using a modified
CTAB method (Cubero et al. 1999). DNA extracts were used for
PCR amplification of the ITS regions, including the 5.8S gene of
the nuclear rDNA. The primers used for amplification were ITS1F
(Gardes and Bruns 1993) and ITS4 (White et al. 1990). The PCR
reaction mixture (50 µL; 10 mM Tris (pH 8.3), 50 mM KCl,
1.5 mM MgCl2, and 50 µg gelatine) contained 1.25 U Dynazyme
Taq polymerase (Finnzymes), 0.2 mM of each of the four dNTPs,
0.5 µM of each primer, and ca. 10–50 ng of genomic DNA. Prod-
ucts were either PEG-precipitated or cleaned using QIAGEN®
quick spin columns (Qiagen). Both complementary strands were
sequenced, using the dRhodamine Terminator Cycle Sequencing
Ready Reaction Kit or Dye Terminator Cycle Sequencing Ready
Reaction Kit (Perkin Elmer), according to the manufacturer’s in-
structions. Sequences were run either on a ABI310 or a ABI373
automated sequencer (ABI). Initial alignments of sequences using
the Pile-up program of the Wisconsin package (Genetics Computer
Group (GCG) sequence analysis software) were manually opti-
mized.
Parsimony and maximum-likelihood analyses were carried out
using PAUP*4.0 (Swofford 1999). Without the flanking regions of
the small subunit and large subunit rDNA, the ITS alignment in-
cluded 581 sites. In-dels and ambiguously aligned parts were ex-
cluded (62 sites); the matrix included 209 informative characters.
Gaps were treated as missing values. In a first parsimony analysis,
the matrix was subjected to 1000 replicates of random sequence
additions using heuristic searches, using tree bisection and recon-
nection (TBR) branch swapping. One thousand bootstrap replica-
tions were performed. A second parsimony analysis was carried
out with the same parameters, but this analysis included only spe-
cies groups (that were found in the first analysis) with variable
growth types and that contained usnic acid as a main compound.
The restricted data set was also subjected to a maximum-likelihood
analysis as implemented in PAUP*4.0, using 1000 replicates of
random addition sequences. Nucleotide frequencies were deter-
mined empirically, using two substitution types, and the transi-
tion/transversion ratio was set to 1.5. All sites were assumed to
evolve at the same rate, using a Hasegawa–Kishina–Yano model,
and a molecular clock was not enforced. To test the hypothesis that
Rhizoplaca is monophyletic, Kishino–Hasegawa tests, as imple-
mented in PAUP*4.0, were applied.
The alignment and further data about the specimens used in this
study can be obtained from the authors upon request. The newly
produced sequences are deposited in EMBL/GenBank. GenBank
accession numbers are given in Table 1.
Protoparmelia badia (Hoffn.) Hafellner was used as the out-
group in our analyses. This lecanoroid lichen was always outside
the Lecanora clade in preliminary analyses, in which Parmelia
sulcata Taylor and Hypogymnia physodes (L.) Nyl. (Parmeliaceae)
were used as outgroups (data not shown). Arctopeltis thuleana was
also included, because it has an umbilicate thallus, but it has usu-
ally been treated separately from Rhizoplaca in the literature.
Results
Six most-parsimonious trees with a length of 880 steps
(consistency index = 0.433; retention index = 0.628) were
found by a heuristic search using P. badia as outgroup. One
of these trees is shown in Fig. 1. The trees are similar to
each other in topology, with only slight re-arrangements in
the group containing Rhizoplaca melanophthalma. The crus-
tose groups of Lecanora rupicola (L.) Zahlbr. and L.allo-
phana Nyl. (= the former subfusca group in a restricted
© 2000 NRC Canada
Arup and Grube 319
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sense) are basal to a branch supported by a bootstrap value
of 87%. This branch includes the “Lecanora dispersa”
group (here represented by Lecanora pruinosa,L. albescens,
Lecanora reuteri,Lecanora contractula, and Arctopeltis thu-
leana) and species groups characterized by usnic acid as a
main secondary compound. The L. dispersa group also in-
cludes an umbilicate species, A. thuleana. All Rhizoplaca
species studied branch with the taxa containing usnic acid,
as do Lecanora species with various types of growth forms.
The Rhizoplaca species do not form a monophyletic branch,
but group with different Lecanora species. A number of
Rhizoplaca species (group B, Fig. 1), including the umbili-
cate type species R.melanophthalma, group together with
Lecanora novomexicana, and this topology has 100% boot-
strap support. Two other umbilicate species, Rhizoplaca pel-
tata and Rhizoplaca chrysoleuca, do not group with this
main assemblage of Rhizoplaca species, but appear else-
where in the tree (groups A and C, Fig. 1). Species with
lobate growth are found in the Lecanora muralis group,
which is supported by a 94% bootstrap value. With 71%
support, R. peltata appears as a sister branch to this clade.
Rhizoplaca chrysoleuca and Rhizoplaca subdiscrepans are
supported as a separate group with 97% support. Analyses
under the constraints that Rhizoplaca is monophyletic and
both Rhizoplaca and Lecanora (including Arctopeltis) are
monophyletic yielded significantly longer trees, which were
rejected in a Kishino–Hasegawa test (Table 2). Similar re-
sults were also obtained in a restricted analysis that included
species groups with usnic acid as a major compound and
groups with various growth forms (Fig. 2). In this analysis,
six most-parsimonious trees (with a length of 503 steps)
with a higher consistency (consistency index = 0.567; reten-
tion index = 0.677) than was found in the larger analysis
were obtained. One of the trees, corresponding to the tree
obtained in maximum-likelihood analysis, is shown in
Fig. 2. Constraint trees with Rhizoplaca as a monophyletic
genus were rejected in a Kishino–Hasegawa test (Table 2).
The differences in the ITS sequences between the differ-
ent species of the core group of Rhizoplaca are generally
small. The branch lengths separating the vagrant species of
© 2000 NRC Canada
320 Can. J. Bot. Vol. 78, 2000
Species or specimen GenBank accession No. Origin
Arctopeltis thuleana Poelt AF159926 Greenland
Lecanora achariana A. L. Sm. AF070019 Sweden
Lecanora albescens (Hoffm.) Branth & Rostr. AF070033 Sweden
Lecanora allophana Nyl. AF159939 Austria
Lecanora campestris (Schaer.) Hue AF159930 Sweden
Lecanora chlorophaeodes Nyl. AF159927 Norway
Lecanora concolor Ramond AF070037 Italy
Lecanora conizaeoides Nyl. ex Crombie AF189717 Sweden
Lecanora contractula Nyl. AF070032 Quebec
Lecanora dispersoareolata (Schaer.) Lamy AF070016 Austria
Lecanora epibryon (Ach.) Ach. AF070014 Austria
Lecanora garovaglii (Körber) Zahlbr. AF189718 Austria
Lecanora intricata (Ach.) Ach. AF070022 Austria
Lecanora macrocyclos (H. Magn.) Degel. AF159933 Sweden
Lecanora muralis (Schreb.) Rabenh. AF159922 Austria
Lecanora novomexicana H. Magn., U162 AF159923 New Mexico
Lecanora novomexicana H. Magn., U363 AF159945 Arizona
Lecanora opiniconensis Brodo AF159928 Arizona
Lecanora phaedrophthalma Poelt AF159938 Tibet
Lecanora polytropa (Ehrh. ex Hoffm.) Rabenh. AF070017 Austria
Lecanora pruinosa Chaub. AF070018 Italy
Lecanora reuteri Schaer. AF070026 Austria
Lecanora saligna (Schrader) Zahlbr. AF189716 Sweden
Protoparmelia badia (Hoffm.) Hafellner AF070023 Austria
Rhizoplaca cerebriformis Ryan ined. AF159942 Idaho
Rhizoplaca chrysoleuca (Sm.) Zopf, U192 AF159924 Arizona
Rhizoplaca chrysoleuca (Sm.) Zopf, U302 AF159940 Kazakhstan
Rhizoplaca cylindrica Ryan ined. AF159941 Idaho
Rhizoplaca haydenii (Tuck.) Follm. AF159937 Idaho
Rhizoplaca idahoensis Rosentreter ined. AF159943 Idaho
Rhizoplaca melanophthalma (DC.) Leuck. & Poelt, U219 AF159929 Arizona
Rhizoplaca melanophthalma (DC.) Leuck. & Poelt, U278 AF159934 Arizona
Rhizoplaca melanophthalma (DC.) Leuck. & Poelt, U281 AF159935 Austria
Rhizoplaca peltata (Ram.) Leuck. & Poelt, U198 AF159925 Arizona
Rhizoplaca peltata (Ram.) Leuck. & Poelt, U282 AF159936 British Columbia
Rhizoplaca subdiscrepans (Nyl.) R. Sant. AF159946 Minnesota
Rhizoplaca subidahoensis Rosentreter ined. AF159944 Idaho
Table 1. The species and specimens studied, with their GenBank accession numbers and origin.
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this core group are not longer than the infraspecific branch
lengths of, for example, R. melanophthalma or R. peltata.
Only in the R. chrysoleuca clade did we observe longer
branches, both between R. subdiscrepans and within R. chry-
soleuca.
Discussion
Rhizoplaca is a well-accepted genus in many lichenology
textbooks and floras, and it is generally assumed that the
higher organization with an umbilicate to foliose thallus rep-
© 2000 NRC Canada
Arup and Grube 321
Lecanora pruinosa
Lecanora albescens
Lecanora reuteri
Arctopeltis thuleana
Lecanora contractula
Lecanora concolor
Lecanora dispersoareolata
Lecanora chlorophaeodes
Lecanora polytropa
Lecanora intricata
Lecanora varia 188
Lecanora varia 165
Lecanora conizaeoides
Lecanora opiniconensis
Rhizoplaca subdiscrepans
Rhizoplaca chrysoleuca 302
Rhizoplaca chrysoleuca 192
Lecanora novomexicana 361
Lecanora novomexicana 162
Rhizoplaca idahoensis
Rhizoplaca haydenii
Rhizoplaca subidahoensis
Rhizoplaca cerebriformis
Rhizoplaca cylindrica
Rhizoplaca melanophthalma 281
Rhizoplaca melanophthalma 278
Rhizoplaca melanophthalma 219
Lecanora phaedrophthalma
Lecanora saligna
Rhizoplaca peltata 282
Rhizoplaca peltata 198
Lecanora muralis
Lecanora achariana
Lecanora macrocyclos
Lecanora garovaglii
Lecanora allophana
Lecanora campestris
Lecanora epibryon
Lecanora rupicola
Lecanora carpinea
Protoparmelia badia
10 changes
61
77
100
91
59
66 61
97
85
53 97
93
82
64
100 98
97
100
71
94 98
100 70
98
85
A
B
C
Fig. 1. One of six most-parsimonious trees of a phylogenetic analysis of the ITS regions and the 5.8S region of Lecanora, Arctopeltis,
and Rhizoplaca, using Protoparmelia badia as the outgroup taxon. Bootstrap percentages greater than 50% are indicated. Rhizoplaca
species are written in boldface type. Groups A–C are discussed in the text.
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resents a natural group. To evaluate this hypothesis, we se-
lected representative taxa of Rhizoplaca that vary in thallus
morphology, chemistry, disc color, and ecology. The type
species, R. melanophthalma, as well as R. peltata and
R. chrysoleuca, have umbilicate thalli (Figs. 3–4), whereas
Rhizoplaca haydenii and some other species (see Fig. 2)
have more or less fruticose types of thallus growth. A com-
plete sampling of all Rhizoplaca species was not attempted,
because more detailed work on species delimitation in this
genus is underway elsewhere.
Our analyses indicate that the generally accepted concept
of Rhizoplaca as a genus separate from Lecanora can be re-
jected. The Rhizoplaca species do not form a monophyletic
group but appear on three different branches of the tree.
Rhizoplaca peltata emerges as a sister group to the L. mur-
alis group, whereas R.chrysoleuca (the type species of the
genus Omphalodina) branches as a sister group to the core
group of Rhizoplaca species. The same branching pattern
was also found with other outgroup taxa, such as members
of the genera Tephromela M. Choisy, Parmelia Ach., and
Hypogymnia (Nyl.) Nyl. (data not shown).
Interestingly, the lobate species L.novomexicana appears
within the R.melanophthalma group, a position strongly
supported by a bootstrap value of 98% (in the restricted
analysis, 99%). This group includes lobate and umbilicate
species, as well as the more or less fruticose thallus types
found in the vagrant species (Figs. 5–9). The latter confirms
the earlier assumption that the North American vagrant mor-
photypes appear to be derived from the R. melanophthalma
complex (Ryan and Nash 1997).
Diversity of growth forms in Lecanora
As is suggested in this study, the growth form of the
thallus is a highly variable characteristic within family Le-
canoraceae. In the study by Arup and Grube (1998), it was
shown that the L.dispersa group and the Lecanora polytropa
group include not only crustose members, but also lobate
and more or less umbilicate species. The umbilicate thallus
form, with both an upper and a lower cortex, as found in
A. thuleana and in several Rhizoplaca species, seems to be
derived from lobate thallus forms without a lower cortex
that have been placed in subgenus Placodium of Lecanora.
A high degree of diversity in thallus morphology is found
particularly in the core group of Rhizoplaca (Fig. 2). With
our phylogenetic analysis, it remains unclear whether the
thallus of L.novomexicana is a reduction of an umbilicate
form (R.melanophthalma or a close relative) to a lobate
thallus, or vice versa. More detailed investigations, including
data from other genes, could address this question. It is
likely that the umbilicate thallus developed into the various
forms occurring in the vagrant species but, again, this needs
to be confirmed by more data. Thalli of R. haydenii vary
from fruticose—richly branched with narrow, more or less
terete branches (or lobes)—to an almost globose structure
formed by the folding of broader and flatter lobes (Fig. 5).
The other vagrant species have rather flat and broad lobes
that do not branch or branch very little (Figs. 6–9). The
whole thallus mostly folds or coils so that the lower cortex,
or lower side, cannot be seen. Although there are consider-
able differences in morphological characters, ITS sequence
diversity is quite low. It might be suggested that this in-
dicates efficient adaptation to particular habitats or envi-
ronmental conditions. Furthermore, the positions of other
species of Rhizoplaca, i.e., R. peltata and R. chrysophthal-
ma, which do not form a monophyletic group with the core
group, indicate several independant origins for umbilicate
growth in groups with lobate growth (Fig. 2).
The evolution of the foliose, umbilicate, or fruticose
growth form is apparently correlated with the development
of a true cortex as an “exoskeleton” (Poelt 1989, 1991). This
type of cortex is found in various genera in the Lecanorales
and has sometimes be used to characterize genera (e.g., Hep-
psora D.D. Awasthi & K.P. Singh; Poelt and Grube 1993).
In our analyses, the true cortex is found in different lineages
in Lecanora, particularly in groups with lobate species. The
development of foliose and fruticose thallus forms within
lobate groups with true upper cortices appears to be a further
consequence, and may be a response or adaptation to envi-
ronment. Sun-exposed nutrient-rich rocks can be one such
environment: A. thuleana inhabits coastal rocks manured by
seabirds, while R. melanophthalma,R. peltata, and R. chry-
© 2000 NRC Canada
322 Can. J. Bot. Vol. 78, 2000
(A) Parsimony scores for trees that include all species in the study.
Tree Length Length difference SD Significantly longer
MP 1 880 (Best)
MP 2 880 0 1.417 61 No
Rhizoplaca monophyletic 908 28 7.780 65 Yes
Rhizoplaca monophyletic 908 28 7.650 41 Yes
Rhizoplaca and Lecanora monophyletic 926 46 9.396 71 Yes
(B) Likelihood scores for trees that include species groups with usnic acid as a major compound and with variable growth.
Tree obtained from the restricted data set ln likelihood Difference in ln likelihood SD Significantly longer
MP 1 2414.136 72 (Best)
MP 2 2414.409 25 0.272 53 1.024 31 No
Rhizoplaca monophyletic 1 2467.310 24 53.173 52 15.097 35 Yes
Rhizoplaca monophyletic 2 2467.601 00 53.464 28 15.270 25 Yes
ML 2414.136 72 0.000 00 0.000 00 No
ML Rhizoplaca monophyletic 2473.782 42 59.645 70 14.961 77 Yes
Note: SD is the statistical standard deviation between trees. If more than one tree was found by heuristic searches (see text), only two trees are
represented in the table. MP, most-parsimonious tree; ML, maximum-likelihood tree.
Table 2. Likelihood variance tests using the method of Kishino and Hasegawa (1989).
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soleuca grow on exposed bird-manured rocks at higher alti-
tudes. On the other hand, the vagrant species studied are
found in windswept steppe-like communities, usually on cal-
careous gravel benches.
The cupula and pycnidial characters
In addition to the umbilicate thallus, Arctopeltis and Rhizo-
placa both possess a cupulate structure below the hymenium.
Such a structure is also found in Lecanora opiniconensis,
Lecanora bipruinosa, and P. badia. Roux et al. (1993)
showed that the cupulate structure with more elongated
hyphae found in Rhizoplaca and L.opiniconensis is distinct
from the pseudoparenchymatous excipulum found in Par-
melia, and does not deter the placing of these taxa in the
Lecanoraceae. Also, the cupulate ascomatal structures of
A. thuleana are different from those in Parmeliaceae (Feige
© 2000 NRC Canada
Arup and Grube 323
Lecanora concolor
Lecanora dispersoareolata
Lecanora chlorophaeodes
Lecanora polytropa
Lecanora intricata
Lecanora opiniconensis
Rhizoplaca subdiscrepans
Rhizoplaca chrysoleuca 302
Rhizoplaca chrysoleuca 192
Lecanora novomexicana
Lecanora novomexicana
Rhizoplaca idahoensis
Rhizoplaca subidahoensis
Rhizoplaca cerebriformis
Rhizoplaca cylindrica
Rhizoplaca melanophthalma 281
Rhizoplaca melanophthalma 278
Rhizoplaca melanophthalma 219
Lecanora phaedrophthalma
Rhizoplaca peltata 282
Rhizoplaca peltata 198
Lecanora muralis
Lecanora achariana
Lecanora macrocyclos
Lecanora garovaglii
Protoparmelia badia
10 changes
71
58
59
57
97
91
81
67
97
99
94
51
64
60
100
50
99
94
Rhizoplaca haydenii
lobate
umbilicate
foliose, little branched
foliose, richly branched
Fig. 2. One of six most-parsimonious trees of a phylogenetic analysis of the ITS regions and the 5.8S region of groups within
Lecanora that have usnic acid as a major secondary compound and with various growth forms, using Protoparmelia badia as the
outgroup taxon. Bootstrap percentages greater than 50% are indicated. Thallus growth form represented by the terminal taxa is mapped
directly on the tree in different shades of grey.
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and Lumbsch 1998). In the present study, species possessing
a cupulate hypothecium do not form one clade but occur
in different lineages of Lecanora. These data suggest that
the structure has developed several times independently, and
mainly in groups with a higher degree of thallus organisation.
The type of conidiophores is constant in Lecanora,
Rhizoplaca, and Arctopeltis, and this does not support sepa-
ration of these genera from each other (Fig. 10). The co-
nidiophores differ slightly from those in Protoparmelia M.
Choisy (Fig. 11) and the Parmeliaceae (Fig. 12). The type of
conidiophore found in Lecanora is often referred to as the
“Placodium type,” or type three (Vobis 1980); however, in
our opinion, conidiophores of this type do not correspond
particularly well with those found in Lecanora s.l., as they
are branched and the conidia are produced acrogenously as
well as pleurogenously. The type of conidiophores in Proto-
parmelia was one of the characters used to suggest a transfer
of the genus to the Parmeliaceae (Henssen 1995), but the co-
nidiophores appear to be more similar to those in Leca-
nora s.l. than to those in the Parmeliaceae. Most conidia
in Lecanora and Rhizoplaca are filamentous and falcate.
However, Lecanora saligna has broadly fusiform to arclike
conidia that are distinct from the common type found in
Lecanora. Nonetheless, the species branches well within Le-
canora in the phylogenetic analysis.
Secondary chemistry
According to Leuckert et al. (1977), one of the reasons for
treating Rhizoplaca as a genus of its own was that it was
chemically homogeneous. They studied the secondary chem-
istry of R.chrysoleuca,R.melanophthalma, and R.peltata
and found several chemical types within them (Table 3).
Usnic acid was found in all three species, in addition to
other compounds that were characteristic of each species,
such as psoromic acid, placodiolic acid, pseudoplacodiolic
acid, pannarin, and zeorin.
© 2000 NRC Canada
324 Can. J. Bot. Vol. 78, 2000
Figs. 3–6. Appearance of some Rhizoplaca species. Fig. 3. Rhizoplaca chrysophthalma. Fig. 4. Rhizoplaca melanophthalma. Fig. 5.
Rhizoplaca haydenii.Fig.6.Rhizoplaca idahoensis. Scale bar=5mm.
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© 2000 NRC Canada
Arup and Grube 325
Figs. 7–9. Appearance of some Rhizoplaca species. Fig. 7. Rhizoplaca subidahoensis.Fig.8.Rhizoplaca cylindrica.Fig.9.Rhizoplaca
cerebriformis. Scale bar=5mm.
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Psoromic acid, as well as usnic acid, is found in the
lobate L. novomexicana, which is closely related to the core
group of Rhizoplaca. However, at lower elevations in south-
western North America, lecanoric acid is often found instead
of psoromic acid in this species. This chemistry corresponds
very well with the compounds found in R. melanophthalma
(compare Table 3 and McCune 1987). Other possible rela-
tives of the Rhizoplaca core group included L.opiniconensis
and Lecanora phaedrophthalma, but chemically these spe-
cies do not fit into this group well. In the most-parsimonious
trees, L.opiniconensis forms a branch with R.chrysoleuca
and R.subdiscrepans (Figs. 1 and 2), but there is no signifi-
cant bootstrap support and secondary chemistry indicates
that R.chrysoleuca could be more closely related to the
Rhizoplaca core group.
The grouping of R. peltata as sister to the L. muralis
group is moderately supported by the bootstrap value of
71% (60% in the restricted data set), as well as by the chem-
istry. Several members of the L.muralis group have both
psoromic acid and zeorin in addition to usnic acid; pannarin
does not occur in any of the species of the L.muralis group
included in this study. On the other hand, psoromic acid and
zeorin are common in Lecanora s.l. and their presence may
not necessarily be considered very strong support for any re-
lationship with R. peltata. The same is true for the related
Rhizoplaca bullata, which was not included in this study.
Morphologically, this species is closely related to R. peltata
but it contains fumarprotocetraric acid (Follmann and
Crespo 1976). This compound is also found sporadically in
other groups of Lecanora species. These data indicate that
the secondary chemistry does not support a monophyletic
genus Rhizoplaca that is distinct from Lecanora. Other
North American species not included in this study, such as
Rhizoplaca glaucophana and Rhizoplaca marginalis, were
transferred to Rhizoplaca by Weber (1979) but are chemi-
cally different (Brodo 1986).
The result that Rhizoplaca is not a monophyletic genus, if
Lecanora is accepted in the current circumscription, has im-
plications for the taxonomy of the Lecanoraceae. However,
before we consider nomenclatural changes, we prefer to wait
for additional support and information from other genes.
Also, more genera related to Lecanora must be included in
future analyses to develop a revised concept of the huge ge-
nus Lecanora; any resulting evaluation of generic segregates
should then consider the criteria suggested by Nimis (1998).
Here we can only outline possible scenarios. Including
© 2000 NRC Canada
326 Can. J. Bot. Vol. 78, 2000
Figs. 10–12. Conidiophores and conidia. Fig. 10. Lecanora muralis. Fig. 11. Protoparmelia badia. Fig. 12. Pleurosticta acetabelum.
Scale bar = 10 µm.
Placodiolic
acid Pseudo-
placodiolic acid Psoromic
acid Lecanoric
acid Pannarin Norstictic
acid Zeorin Terpenes or
triterpenes Unknowns
R. chrysoleuca x x (x)(x)
R. melanophthalma (x)x(x)
R. peltata (x)xx(x)x
R. subdiscrepans x
L. novomexicana (x)
L. opiniconensis xx
L. phaedrophthalma x (x)
L. muralis (x)x
Note: “x” indicates a major compound and “(x)” indicates a compound found occasionally.
Table 3. Secondary chemistry of some species of Rhizoplaca and Lecanora; all species contain usnic acid in addition to the com-
pounds shown.
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Arup and Grube 327
Rhizoplaca in the large genus Lecanora implies that addi-
tional genera ought to be considered as potential candidates
for merging with Lecanora. On the other hand, if we agreed
with Leuckert et al. (1977) that the difference between the
L. allophana group and Rhizoplaca merits “more than ge-
neric rank,” then we would face substantial taxonomic reor-
ganisation and the generic splitting of lecanoroid lichens. In
this case, the level at which genera should be segregated is
still a matter of discussion. If Rhizoplaca s.s. were to include
only the R. melanopthalma group and the vagrant species,
then the generic name Omphalodina would have to be con-
sidered for the R. chrysoleuca group, and the L. muralis
group could be merged with R. peltata under Protoparmelio-
psis M. Choisy. We doubt, however, that this would be a
good solution, since many other Lecanora species would
then have an uncertain taxonomic position. In any case, a
concept based on molecular data will lead to genera that are
difficult to circumscribe with the traditionally used morpho-
logical characters. It is therefore important that phylogenetic
studies at the genus level in the Lecanorales be accompanied
by further investigation of non-molecular characters.
Acknowledgements
We are grateful to R. Rosentreter, T. Nash III, and B.
Ryan for the loan of Rhizoplaca specimens. This work was
supported by grant P11806-GEN of the Austrian Science
Foundation to M.G.
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