As
an undergraduate student back in Panama we took a class by Noris Salazar Allen on bryophyte morphology and
systematics. One of the final projects consisted of collecting species of
bryophytes. One of the commonest plants collected by all students was the cloud
forest inhabitant Dumortiera hirsuta.
It grows in wet places and close to streams, in close association with Monoclea gottschei and sometimes with
the hornwort Nothoceros vincentianus.
It is widely distributed and rather common in tropical America. It is also found in North America, Africa, mainland
Europe and England, although unlike in my homeland, the
plant is considered rare in England (see Porley 2013)
Dumortiera is a rather conspicuous plant with a
large thallus up to 20 cm long (Gradstein et al. 2001),
deep green colour, lacking pores, sometimes with vestigial air chambers and
typically with hairs along the thallus margins (hence the name hirsuta). On the ventral part of the
thallus the rhizoids are concentrated along the middle line and resemble a
midrib. The male receptacles are nearly sessile while female receptacles are on
an elongate stalk. There are no known forms of asexual reproduction. The
circumscription of two subspecies (the glossy D. hirsuta subsp. hirsuta, typified
by material from Jamaica and the velvety
D. hirsuta subsp. nepalensis, typified
by material from Nepal) has been contentious, a recurrent theme in widespread
species. The two subspecies have been traditionally separated by the dorsal
smooth surface of the thallus, with few (if present then rather spherical) or
absent papilliform cells in D. hirsuta subsp. hirsuta, while subspecies nepalensis has vestigial air chambers
and papilliform ovoid-pointed cells on its dorsal surface (Schuster 1992).
Majority
rule consensus tree from maximum parsimony analysis of the four locus matrix (rbcL, rpoC1, psbA-trnH and the ITS region) from Forrest et al. (2011). |
Recently,
Forrest et al. (2011)
sequenced 50 accessions of Dumortiera,
mostly from Panama and Costa Rica, but with representatives from continental
Europe, England, Ireland, Nepal, India, Malaysia, Mexico and the USA.
Surprisingly (or not, considering the cryptic species mentioned in the last
blog) there are two main clades, a central American one (Panama/Costa Rica) consisting
of the plants that have a velvety appearance (which have been previously referred
to subs. nepalensis) and a widespread
clade that contains plants from Central America and the rest of the world. An English
Dumortiera accession is related to
French and Irish collections.
The
morphological part of Forrest et al.’s
study describes three main phenotypes within the species: (A) mostly glabrous thalli
with remnants of air chambers and a few dorsal papillae; (B) glabrous thalli with
remnants of air chambers only at the apex. Both these morphotypes have a hairy thallus
border with abundant, distinctive marginal trichomes. The third morphotype (C)
is characterized by velvety thalli with remnants of air chambers filled with
dorsal papillae of variable sizes, without marginal trichomes. The velvety Dumortiera (subs. nepalensis) is from Nepal and the study shows that it is not
genetically related to the Central American plants.
Based
on Forrest et al.’s work there are at least two well-defined species within Dumortiera, one restricted to Central
America, and one with a more widespread distribution. However, confusing the issue somewhat, the
morphological features do not seem to be useful to circumscribe the widespread
clade! A monograph is really needed to relate morphology to these robust
molecular lineages.
A
recurrent theme in bryophyte systematics is that widespread species have highly
structured genetic clades that are not associated with clear-cut morphological
characters. The implications are not only for taxonomists to untangle this
problem, but also for conservation. What needs protection, restricted clades or
widespread ones? It is possible that
further sampling (for example within Africa and South America) will uncover more
distinct lineages. Even in countries
with really well-known floras, such as the UK, where Dumortiera hirsuta is listed as vulnerable, there are no specific
conservation actions. In the tropics the situation is far more complex. A potentially exciting worldwide
phylogeographic study (along with a taxonomic treatment) is required to sort
out whether Dumortiera is a worldwide
traveller that originated in the tropics, how many species there actually are within
this lineage, and how to promote the conservation of this complex thalloid
liverwort.
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