BRIEF COMMUNICATION

doi:10.1111/j.1558-5646.2009.00787.x

AND IF ENGLER WAS NOT COMPLETELYWRONG? EVIDENCE FOR MULTIPLEEVOLUTIONARY ORIGINS IN THE MOSS FLORAOF MACARONESIADelphine A. Aigoin,1,2,3 Nicolas Devos,1,4 Sanna Huttunen,5,6 Michael S. Ignatov,7,8

Juana M. Gonzalez-Mancebo,9,10 and Alain Vanderpoorten1,11

1Institute of Botany, University of Liege, 27 Blvd du Rectorat, B22, Sart Tilman, 4000 Liege, Belgium2E-mail: Delphine.Aigoin@ulg.ac.be

3Institute of Evolutionary Sciences, University of Montpellier II, Place Eugene Bataillon, 34095 Montpellier Cedex 5, France4E-mail: ndevos@ulg.ac.be

5Laboratory of Genetics, Department of Biology, University of Turku, 20014 Turku, Finland6E-mail: shuttu@utu.fi

7Main Botanical Garden of Russian Academy of Sciences, Botanicheskaya 4, 127276 Moscow, Russia8E-mail: misha_ignatov@list.ru

9Department of Botany, University of La Laguna, 38271 La Laguna, Tenerife, Canary Islands, Spain10E-mail: jglezm@ull.es11E-mail: A.Vanderpoorten@ulg.ac.be

Received March 27, 2009

Accepted June 23, 2009

The Macaronesian endemic flora has traditionally been interpreted as a relict of a subtropical element that spanned across Europe

in the Tertiary. This hypothesis is revisited in the moss subfamily Helicodontioideae based on molecular divergence estimates

derived from two independent calibration techniques either employing fossil evidence or using an Monte Carlo Markov Chain

(MCMC) to sample absolute rates of nucleotide substitution from a prior distribution encompassing a wide range of rates docu-

mented across land plants. Both analyses suggest that the monotypic Madeiran endemic genus Hedenasiastrum diverged of other

Helicodontioideae about 40 million years, that is, well before Macaronesian archipelagos actually emerged, in agreement with

the relict hypothesis. Hedenasiastrum is characterized by a plesiomorphic morphology, which is suggestive of a complete morpho-

logical stasis over 40 million years. Macaronesian endemic Rhynchostegiella species, whose polyphyletic origin involves multiple

colonization events, evolved much more recently, and yet accumulated many more morphological novelties than H. percurrens.

The Macaronesian moss flora thus appears as a complex mix of ancient relicts and more recently dispersed, fast-evolving taxa.

KEY WORDS: Bryophytes, fossils, macronesian endemism, molecular dating, morphological evolution.

Macaronesia is a string of North Atlantic volcanic islands (the

Azores, Madeira, Canaries, and Cape Verde) that emerged 0.4–

20 million years ago and are characterized by high rates of en-

demism (see Juan et al. 2000 for review). Engler (1879), fol-

lowed by many biogeographers (see Vanderpoorten et al. 2007

for review), proposed that Macaronesian endemics are the relics

3 2 4 8C© 2009 The Author(s). Journal compilation C© 2009 The Society for the Study of Evolution.Evolution 63-12: 3248–3257

BRIEF COMMUNICATION

of biota that were widespread across Europe during the Tertiary

and decimated on the continent during the glaciations. In con-

trast with the expectations of the refugium concept, however,

several lines of evidence from analyses of moss species dis-

tributions (Vanderpoorten et al. 2007) and molecular evolution

rates in angiosperms (Carine 2005) have recently questioned En-

gler’s hypothesis. In mosses, the hypothesis of extinction of a

Tertiary flora in all but Macaronesian areas is solely supported

by extremely limited fossil evidence in the genus Echinodium

(Frahm 2004). This interpretation is, however, weakened by the

polyphyletic origin of the genus (Stech et al. 2008), thereby

raising doubts about the actual sister relationship between fos-

sil and extant Macaronesian Echinodium species. By contrast,

the nested phylogenetic position of the Azorean endemic liver-

wort Leptoscyphus azoricus within a Neotropical clade (Devos

and Vanderpoorten 2009); the close biogeographic affinities of

several Macaronesian groups with the North and South Ameri-

can continents (see Vanderpoorten et al. [2007] for review); and

the polyphyletic origin among Macaronesian populations of the

moss Grimmia montana, which are genetically identical or most

closely related to those of different continents (Vanderpoorten

et al. 2008) all point to recurrent migrations between the latter

and the Macaronesian archipelagos, potentially followed by in situ

speciation.

The continental extinction and recent speciation hypothe-

ses make different predictions regarding the rates of speciation

and morphological evolution. In fact, as opposed to neoendemics,

which originated from local speciation processes and often under-

went spectacular adaptive radiations involving a sudden burst of

morphological diversification (see Gillepsie and Roderick [2002]

for review), paleoendemics, which survived continental extinc-

tions on the islands, have most often retained a highly conserved

morphology for millions, or tens of million years, to such an extent

that extant taxa appear conspecific with fossil species (Sunding

1979).

In this article, we revisit hypotheses on the origin of Mac-

aronesian endemism in the mosses from the Brachytheciaceae,

subfamily Helicodontioideae. This group includes several Mac-

aronesian endemics, namely the monotypic Madeiran Hedenasi-

astrum percurrens, and three Rhynchostegiella species: Rhyn-

chostegiella bourgeana and R. trichophylla, which are restricted

to the Canary Islands, and R. macilenta, whose distributions

span Madeira and the Canaries. In addition, and unlike most

bryophytes, a fairly well-documented fossil record is available

(Miller 1984). We produced a molecular phylogeny of the Heli-

codontioideae to test the hypothesis of a radiation within Rhyn-

chostegiella and date the origin of its Macaronesian endemic lin-

eages, contrasting the results derived from a fossil calibration and

an analysis employing absolute rates of molecular evolution. We

then used the phylogeny to test the hypothesis of a long mor-

phological stasis since the Tertiary period among Macaronesian

endemics.

Material and MethodsTAXONOMIC AND MORPHOLOGICAL CHARACTER

SAMPLING

The 17 genera of Helicodontioideae as circumscribed by Aigoin

et al. (2009) were sampled (Table 1). Each genus was represented

by one to three species, with a special emphasis on Rhynchoste-

giella, for which all eight species were sampled. Three other

species, namely R. papuensis, R. leptoneura, and R. muriculata,

clearly do not belong to the genus, and the appropriate taxonomic

changes will be presented elsewhere. Aerobryidium filamentosum,

a species of the sister family Meteroriaceae, as well as representa-

tive taxa of each of the three subfamilies of Brachytheciaceae was

sampled as outgroups (Table 1). Forty-three morphological char-

acters that are variable across the Helicodontioideae, including

34 gametophytic and nine sporophytic ones, were scored for each

of the sampled taxa (Appendices S1 and S2) (see Huttunen and

Ignatov [2004] for a thorough account on character significance

and description).

MOLECULAR PROTOCOLS AND PHYLOGENETIC

ANALYSES

Four chloroplast regions (trnL-trnF, atpB-rbcL, psbT-psbH, and

psbA-trnH) were selected for exhibiting the appropriate level of

variation at the genus level in the Brachytheciaceae (Huttunen and

Ignatov 2004). DNA extraction, PCR and sequencing protocols,

sequence editing, alignment, indel scoring, and selection of mod-

els for DNA substitutions and indel evolution follow Aigoin et al.

(2009). Phylogenetic reconstruction was conducted with MrBayes

3.1.2. Four independent Monte Carlo Markov Chains (MCMCs)

of 2,000,000 iterations each were run and trees and model param-

eters were sampled every 10,000 generations. The convergence

of the MCMCs was verified visually from the likelihood values,

and trees of the “burn-in” were discarded.

A significant departure of alternative topologies involving a

monophyletic origin of the three Macaronesian endemic Rhyn-

chostegiella species, namely R. bourgeana, R. macilenta, and R.

trichophylla, was tested by constrained analyses. The MCMC

analysis described above was rerun under the constraint that only

trees fitting with a monophyletic origin of the Macaronesian en-

demic Rhynchostegiella species were sampled. We then deter-

mined whether the constraint induced a significant loss of like-

lihood by means of the Bayes factors, as assessed by twice the

difference in the log marginal likelihood between the two runs.

MOLECULAR DATING

Times of divergence were calculated to determine the origin

of the most recent common ancestor (hereafter, MRCA) of H.

EVOLUTION DECEMBER 2009 3 2 4 9

BRIEF COMMUNICATION

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3 2 5 0 EVOLUTION DECEMBER 2009

BRIEF COMMUNICATION

Ta

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2–

percurrens and of the three Macaronesian endemics of Rhyn-

chostegiella. Examination of rate variation among branches of the

phylogeny suggested a strong departure of the sequence data from

the molecular clock (see below). Divergence times were therefore

estimated using a Bayesian MCMC method under a relaxed-clock

model employing an uncorrelated lognormal model of rate vari-

ation among branches in the tree as implemented by BEAST

1.4.8. Nonequivocal Miocene fossils of Cirriphyllum piliferum

and Oxyrrhynchium hians, and Pliocene fossils of Clasmatodon

parvulus (Miller 1984) were used for calibration at three internal

nodes. In bryophytes, wherein the probability of fossilization is

very low owing to the absence of lignified tissues and much re-

duced cuticle, the presence of a species is likely to be recorded

in the sediment only well after its actual phylogenetic origin. We

therefore used asymmetric distribution priors with a mode at the

beginning of the period considered and asymptotically skewed

toward the end of it (Fig. 1).

In a second set of analyses, absolute nucleotide substitu-

tion rates documented for a large number of plant lineages (in-

cluding bryophytes) were used. Accordingly, a normal distribu-

tion, with a mean and standard deviation of 5.0 × 10−10 and

10−10 substitutions/site/year, respectively, which corresponds to

the average absolute substitution rate of cpDNA across land plants

and largely encompasses their variation range (see Schnabel and

Wendel [1998] for review), was used as a prior on the absolute

rates of evolution for the four cpDNA regions combined.

Although BEAST allows for topologies, branch lengths, and

rates to be coestimated, we chose to perform the dating analyses

onto topologies that were derived independently from the kind of

calibration used. Therefore, we constrained the topology to match

the 50% majority-rule consensus of the trees sampled from the

posterior probability distribution generated by MrBayes, but used

the MCMC implemented by BEAST to sample branch lengths

and substitution rates depending on their posterior probabilities.

A Yule prior on branching rates was employed and two indepen-

dent MCMC analyses were each run for 10,000,000 steps. Param-

eter values were sampled every 1000 cycle over the 10,000,000

MCMC steps. Convergence and acceptable mixing of the sam-

pled parameters was checked using Tracer 1.4. After discarding

the burn-in steps, the two runs were combined to obtain an es-

timate of the posterior probability distribution of the divergence

dates of the ancestral nodes.

ANCESTRAL CHARACTER STATE RECONSTRUCTIONS

Ancestral character state reconstructions were performed to con-

trast the hypotheses that Macaronesian endemics are characterized

by plesiomorphic or derived character states. All reconstructions

were performed after pruning the outgroups from the trees. The

probabilities of a change in a branch were calculated by esti-

mating the instantaneous forward and backward rates among the

EVOLUTION DECEMBER 2009 3 2 5 1

BRIEF COMMUNICATION

Figure 1. Fifty percent majority-rule consensus tree from the Bayesian analysis of four chloroplastic genes in Helicodontiodeae, with

branch lengths averaged over the 284 trees sampled from the posterior probability distribution. Posterior probabilities are indicated under

each branch. Fossil calibration points are labeled by stars and the range of the prior distribution encompassing the geological era during

which the fossil was found is illustrated in boxes. The dates indicated at five nodes (black circles) correspond to the median (and 95%

confidence interval) of the age of selected nodes, as inferred from the molecular dating analysis when the fossil calibration (F) or absolute

substitution rates of chloroplastic DNA (R) were used. The four Macaronesian endemic species of Helicodontioideae appear in bold.

two states by implementing the Markov model of “Multistate” in

BayesTraits 1.0.

To contrast alternative hypotheses regarding the morphol-

ogy of the MRCA of the Macaronesian endemics, we used the

“local” approach, wherein the significance of the reconstruction

is explicitly tested at each node of interest (Pagel 1999). For

that purpose, we fixed each of the MRCAs of H. percurrens and

Rhynchostegiella at one of the two states it can take. Then, an

MCMC was used to visit the sample of trees generated by the

MrBayes analysis and the space of rate parameter values. In the

absence of information on rates, uniform distributions ranging

between 0 and 100 were used as priors. The likelihood of the

new combination of a rate and a tree was calculated and this new

state of the chain was accepted or rejected following evaluation

by the Metropolis–Hastings term. The rate, at which parame-

ters were changed (“ratedev”), was set at the beginning of each

run so that the acceptance rate of the proposed change globally

ranges between 20% and 40%. The chain was run for 10,000,000

generations and was sampled for rate parameters every 10,000

generations. A second, independent chain was run to sample rate

3 2 5 2 EVOLUTION DECEMBER 2009

BRIEF COMMUNICATION

parameters and derive overall likelihoods of the reconstructions

when the node of interest was fixed at its alternative state. Bayes

factors were then used to determine the support for alternative

state at each node of interest.

ResultsPHYLOGENETIC RELATIONSHIPS

The chloroplast matrix contains 19% variable sites. The 50%

majority-rule consensus of the 284 trees sampled from the poste-

rior probability distribution is presented in Figure 1. Macaronesian

endemics within the Helicondontioideae appear at the two extrem-

ities of the phylogeny. The Madeiran endemic Hedenasiastrum

percurrens is sister to all other genera of the Helicodontioideae,

and this relationship is supported with a posterior probability

(hereafter, p.p.) of 1.00. By contrast, Rhynchostegiella is one of

the most recently diverging groups of species of the Helicodon-

tioideae. Within Rhynchostegiella, the sub-Saharan African R.

holstii is part of a polytomy with two other clades. The first clade

includes the Canarian endemics R. bourgeana and R. trichophylla

with a p.p. of 0.98. Within the second clade, the Macaronesian

endemic R. macilenta is resolved as sister to a Madeiran accession

of R. teneriffae with a p.p. of 0.96. The hypothesis of a mono-

phyletic origin of the three Macaronesian endemic species can be

significantly rejected. In fact, constraining all three Macaronesian

endemic species to monophyly resulted in a significantly lower

log marginal likelihood by comparison with the unconstrained

analysis (log marginal likelihood of −6884.07 and −6861.42 for

the constrained and unconstrained analyses, respectively).

MOLECULAR DIVERGENCE DATING

The coefficient of variation of rates among branches of the phy-

logeny was 0.63 (95% highest posterior density 0.44–0.83) for the

first analysis (fossil calibration) and 0.60 (95% highest posterior

density 0.43–0.77) for the second one (rate sampling from a prior

distribution). This suggests a strong departure of the data from a

molecular clock, a condition in which the coefficient of variation

equals zero. The two kinds of calibration used for molecular dat-

ing by a relaxed-clock model provided congruent results regard-

ing both the medians of the posterior probability distributions and

their 95% confidence intervals (Fig. 1). Hedenasiastrum percur-

rens emerged 38 [20;74] million years with the fossil calibration

and 42 [25;65] when absolute substitution rates were employed.

The divergence and diversification of Rhynchostegiella, respec-

tively, date back to 20 [9;35] and 11 [4;20] million years with

the fossil calibration and 22 [13;36] and 12 [6;20] with absolute

rates of molecular evolution. The MRCA of the Macaronesian

endemics R. bourgeana and R. trichophylla was dated back to 7

[2;14] million years with the fossil calibration and 8 [3;15] when

a distribution of absolute substitution rates was used as a prior,

whereas R. macilenta is estimated to have diverged more recently,

1 [0;4] million year according to the fossil calibration, and 1 [0;4]

when absolute rates were used (Fig. 1).

ANCESTRAL CHARACTER STATE RECONSTRUCTIONS

The marginal log-likelihoods of the reconstruction of ancestral

morphological character states at the MRCA of the Macaronesian

endemics are presented in Table 2. When the MRCA of the Heli-

codontioideae was constrained to be morphologically identical to

the Madeiran endemic H. percurrens, the marginal log-likelihoods

of the reconstruction were significantly higher for 20 of the 32

investigated gametophytic characters. For the remaining 12 char-

acters, the marginal log-likelihood obtained after fixing the root

of the Helicodontioideae at one or the alternative state were not

significantly different (i.e., the Bayes factors were <2), so that the

state at the root was ambiguous for those characters. Altogether,

the two Canarian endemics R. bourgeana and R. trichophylla dif-

fer from the MRCA of the genus by six character states (#12, 13,

15, 20, 23, 26). Finally, R. macilenta, which is the phylogeneti-

cally most recently diverging Macaronesian endemic within the

Helicodontioideae, differs from the MRCA of Rhynchostegiella

by nine character states (#5, 10, 11, 12, 13, 18, 20, 26, and 35).

DiscussionThe two calibration techniques used in the present study, that

is the use of fossils and the sampling of absolute substitution

rates from a prior distribution encompassing a wide range of

rates documented across land plants, rely on completely different

assumptions. Yet, they returned highly congruent results, which

strongly reinforces the confidence in the molecular dating in-

ferences. The MRCA of Rhynchostegiella dates back to about

10 million years. This timing is compatible with both a paleo-

and a neo-endemic origin of its Macaronesian endemic species.

The polyphyletic origin of the latter, however, does not lend sup-

port to Engler’ refugium hypothesis. Like in some angiosperms

(see Carine et al. [2004] for review), the colonization of Mac-

aronesia by Rhynchostegiella species seems to have involved at

least two dispersal events. Rhynchostegiella was one of the few

bryophyte genera, wherein several Macaronesian endemics had

been described, and therefore was one of the few candidates for

adaptive radiations. The polyphyletic origin of its Macaronesian

endemics invalidates that hypothesis, although the sister relation-

ship between R. bourgeana and R. trichophylla suggests that local

speciation may, to a minimal extent, have happened. Furthermore,

and although this needs to be confirmed by additional sampling,

the Macaronesian endemic R. macilenta is resolved as a sister to

a sympatric accession of R. teneriffae, rendering the latter species

paraphyletic. Such a situation has been recently increasingly de-

scribed in other bryophyte species and has been interpreted in

EVOLUTION DECEMBER 2009 3 2 5 3

BRIEF COMMUNICATION

Ta

ble

2.

An

cest

ralc

har

acte

rst

ate

reco

nst

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on

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ics

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the

Hel

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Ap

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(BF)

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the

log

of

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har

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nic

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(HM

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stat

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nce

of

2–5

con

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evid

ence

(∗),

5–10

stro

ng

evid

ence

(∗∗ )

,an

d>

10ve

ryst

ron

gev

iden

ce(∗

∗∗).

The

stat

ere

turn

ing

the

hig

hes

tlo

gm

arg

inal

likel

iho

od

isu

nd

erlin

ed.

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ract

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hara

cter

stat

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BF

HM

BF

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Con

stra

ined

R.

R.

R.

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stra

ined

perc

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nsM

RC

Abo

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ana

tric

hoph

ylla

mac

ilen

taR

hync

host

egie

lla

MR

CA

Cha

ract

er1

00/

1−1

1.35

/−1

5.51

8.3∗∗

00

00/

1−1

2.21

/−1

9.61

14.8

∗∗∗

Cha

ract

er2

00/

1−2

1.61

/−2

1.65

0.1

11

00/

1−2

2.06

/−2

1.33

1.5

Cha

ract

er3

10/

1−1

4.65

/−1

4.91

0.5

–0

00 /

1−1

4.14

/−2

0.39

12.5

∗∗∗

Cha

ract

er4

00/

1−1

3.34

/−1

6.75

6.8∗∗

00

00/

1−1

3.24

/−2

0.53

14.6

∗∗∗

Cha

ract

er5

00/

1−1

4.93

/−1

8.07

6.3∗∗

00

10/

1−1

4.47

/−2

1.95

15.0

∗∗∗

Cha

ract

er6

00/

1−1

1.46

/−1

5.41

7.9∗∗

00

00/

1−1

1.73

/−1

9.82

16.2

∗∗∗

Cha

ract

er7

00/

1−9

.71/

−14.

659.

9∗∗0

00

0/1

−9.9

7/−1

9.28

18.6

∗∗∗

Cha

ract

er8

00/

1−2

2.97

/−2

3.2

0.5

–0

00/

1−2

2.92

/−2

3.27

0.7

Cha

ract

er9

00 /

1−2

2.42

/−2

3.61

2.4∗

00

00/

1−2

2.19

/−2

4.79

5.2∗∗

Cha

ract

er10

00/

1−1

8.79

/−2

0.84

4.1∗

00

10/

1−1

8.68

/−2

2.07

6.8∗∗

Cha

ract

er11

00/

1−2

1.94

/−2

2.81

1.7

00

10/

1−2

1.55

/−2

3.59

4.1∗

Cha

ract

er12

00/

1−1

8.46

/−2

0.41

3.9∗

01

00/

1−2

0.39

/−1

8.42

3.9∗

Cha

ract

er13

00/

1−2

1.92

/−2

2.54

1.2

01

00/

1−2

3.39

/−2

1.71

3.4∗

Cha

ract

er14

10/

1−1

6.66

/−1

6.71

0.1

11

10/

1−2

1.02

/−1

5.79

10.5

∗∗∗

Cha

ract

er15

00/

1−9

.95/

−15.

3310

.8∗∗

∗0

10

0/1

−10.

82/−1

6.17

10.7

∗∗∗

Cha

ract

er16

00/

1−1

9.42

/−2

1.46

4.1∗

00

00/

1−1

9.31

/−2

4.25

9.9∗∗

Cha

ract

er17

00/

1−1

3.66

/−1

6.93

6.5∗∗

00

00/

1−1

3.42

/−2

1.14

15.4

∗∗∗

Cha

ract

er18

00/

1−2

3.05

/−2

3.82

1.5

00

10/

1−2

2.90

/−2

4.02

2.2∗

Cha

ract

er19

10/

1−2

0.39

/−2

0.49

0.2

01

10/

1−2

0.74

/−2

0.34

0.8

Cha

ract

er20

00/

1−1

7.95

/−1

9.89

3.9∗

01

10/

1−1

5.98

/−2

1.13

10.3

∗∗∗

Cha

ract

er21

00/

1−1

4.77

/−1

7.4

5.3∗∗

00

00/

1−1

4.88

/−2

1.03

12.3

∗∗∗

Cha

ract

er22

00/

1−2

1.27

/−2

2.23

1.9

–0

00/

1−2

1.16

/−2

2.56

2.8∗

Cha

ract

er23

00/

1−2

2.55

/−2

3.01

0.9

01

00/

1−2

2.13

/−2

4.34

4.4∗

Cha

ract

er24

00/

1−1

4.02

/−1

7.25

6.5∗∗

00

00/

1−1

4.13

/−2

0.75

13.2

∗∗∗

Cha

ract

er25

00/

1−1

1.39

/−1

4.76

6.7∗∗

–0

00/

1−1

1.23

/−1

8.48

14.5

∗∗∗

Cha

ract

er26

10/

1−2

3.61

/−2

2.71

1.8

10

00/

1−2

4.38

/−2

2.19

4.4∗

Cha

ract

er27

10/

1−1

1.49

/−1

0.52

1.9

1–

–0/

1−1

3.75

/−1

0.50

6.5∗∗

Cha

ract

er28

00/

1−1

3.5/

−14.

211.

41

––

0/1

−13.

50/−1

4.40

1.8

Cha

ract

er29

00 /

1−1

5.98

/−1

8.39

4.8∗

00

00/

1−1

5.79

/−2

2.01

12.4

∗∗∗

Cha

ract

er30

00/

1−1

8.83

/−2

0.96

4.3∗

00

00/

1−1

8.78

/−2

3.92

10.3

∗∗∗

Co

nti

nu

ed.

3 2 5 4 EVOLUTION DECEMBER 2009

BRIEF COMMUNICATION

Ta

ble

2.

Co

nti

nu

ed.

Cha

ract

erst

ate

ofC

hara

cter

stat

esof

HM

BF

HM

BF

H.

Con

stra

ined

R.

R.

R.

Con

stra

ined

perc

urre

nsM

RC

Abo

urge

ana

tric

hoph

ylla

mac

ilen

taR

hync

host

egie

lla

MR

CA

Cha

ract

er31

00/

1−1

7.11

/−1

9.02

3.8∗

00

00/

1−1

6.87

/−2

2.17

10.6

∗∗∗

Cha

ract

er32

00/

1−1

0.21

/−1

4.69

9.0∗∗

00

00/

1−1

0.63

/−1

9.37

17.5

∗∗∗

Cha

ract

er33

–0/

1–

–0

00

0/1

−12.

19/−1

7.84

11.3

∗∗∗

Cha

ract

er34

–0/

1–

–0

00

0/1

−10.

22/−1

7.89

15.3

∗∗∗

Cha

ract

er35

–0/

1–

–0

01

0/1

−18.

08/−2

0.17

4.2∗

Cha

ract

er36

–0/

1–

–0

00

0/1

−11.

73/−1

7.15

10.8

∗∗∗

Cha

ract

er37

–0/

1–

–0

00

0/1

−14.

79/−1

8.41

7.2∗∗

Cha

ract

er38

–0/

1–

–0

00

0/1

−15.

89/−1

6.93

2.1∗

Cha

ract

er39

–0/

1–

–0

00

0/1

−12.

97/−1

6.73

7.5∗∗

Cha

ract

er40

–0/

1–

–0

00

0/1

−13.

20/−1

6.78

7.2∗∗

Cha

ract

er41

–0/

1–

–0

00

0/1

−11.

62/−1

5.76

8.3∗∗

Cha

ract

er42

–0/

1–

–0

00

0/1

−11.

85/−1

6.44

9.2∗∗

Cha

ract

er43

–0/

1–

–0

00

0/1

−10.

71/−1

7.63

13.8

∗∗∗ terms of recent speciation and incomplete lineage sorting (see

Sotiaux et al. [2009] for review), thereby reinforcing the idea of

a neoendemic origin of R. macilenta.

Although the polyphyletic origin and recent evolution of the

Macaronesian endemic Rhynchostegiella species is thus sugges-

tive of multiple colonization events followed by rather recent di-

vergence, the Madeiran endemic moss H. percurrens diverged

about 40 million years, that is well before Madeira actually

emerged, 5.2 million years. This time frame, together with the

fairly long branch leading to this unique species, is suggestive

of numerous extinctions and a relictual origin. Hedenasiastrum

percurrens actually becomes the only clear-cut documented case

of relict in the Macaronesian bryophyte flora. In the context of a

“dispersalist counter-revolution” fueled by the outcome of recent

molecular phylogenies and molecular dating studies (de Queiroz

2005), and of a reassessment of the recent origin of emblematic is-

land endemics (e.g., Goldberg et al. 2008; Grandcolas et al. 2008),

including Macaronesia (e.g., Jordal and Hewitt 2004; Emerson

and Oromı 2005; Dimitrov et al. 2008), the present study argues

for a pluralistic view of Macaronesian biogeography. Hedenasias-

trum percurrens thus falls within the increasingly limited category

of confirmed Tertiary relicts. The acceptance of a relictual origin

of H. percurrens, together with its morphological identity with

the MRCA of the Helicodontioideae, dated at 40 million years,

lends support to the traditional view of bryophytes as “unmoving

sphinxes of the past” (see Devos and Vanderpoorten [2009] for

review). In fact, the morphological similarity between extant and

fossil species suggests that some groups of mosses have persisted

with little morphological change for at least 80 million years

(see Devos and Vanderpoorten [2009] for review). The question

of whether this similarity is indeed due to the direct sister rela-

tionship or homoplasy remains, however, open. For example, the

oldest liverwort fossil, the Devonian Pallaviciinites devonicus, ex-

hibits a striking resemblance with the unrelated Pallavicinia and

Symphyogyna (Heinrichs et al. 2007), suggesting that the similar-

ity between fossil and extant taxa likely results from homoplasy.

Thus, although evidence for cryptic speciation in bryophytes

is mounting (see Devos and Vanderpoorten [2009] for review),

morphological stasis over periods of time of a range of tens of

million years actually appears as an extremely rare phenomenon.

In contrast, fast rates of morphological evolution or diversification

have been repeatedly reported in bryophytes (Shaw et al. 2003;

Wall 2005; Devos and Vanderpoorten 2009; Sotiaux et al. 2009).

In the case of H. percurrens, however, although character evolu-

tion might be constrained, so that all the space of morphologies

cannot be necessarily explored (Beldade et al. 2002), convergence

or parallelism occurring to develop what is the same taxon two

or more times is, arguably, less likely than plesiomorphy (Zander

2008). The retention of so many plesiomorphic traits during a 40-

million-year period is remarkable and can be compared to other

EVOLUTION DECEMBER 2009 3 2 5 5

BRIEF COMMUNICATION

spectacular examples of living fossils (see Lee et al. [2006] for

review). Surprisingly, and despite their much more recent origin,

all three Macaronesian endemic Rhynchostegiella species accu-

mulated many more morphological novelties than H. percurrens.

Although the remarkable stasis of H. percurrens might originate

from stabilizing selection, the reasons for such striking differences

in evolutionary rates within the same group of mosses remain

completely unexplained.

ACKNOWLEDGMENTSDA, ND, and AV acknowledge financial support from the Belgian Fundsfor Scientific Research (F.R.S.–FNRS) and the Leopold III Funds, andMI the RFBR 07-04-00013. Many thanks are due to M. Carine, P.-H.Fabre, R. G. Gillepsie, F. Kjellberg, and three anonymous reviewers fortheir constructive comments on an earlier draft of this article.

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Supporting InformationThe following supporting information is available for this article:

Appendix S1. List of 43 morphological binary characters scored on the sample of taxa from the Helicodontioideae.

Appendix S2. Matrix of 43 morphological characters (see Appendix S1) scored for taxa of the Helicodontioideae used in the

present study.

Supporting Information may be found in the online version of this article.

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Please note: Wiley-Blackwell is not responsible for the content or functionality of any supporting information supplied by the

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