SHAW, JON. Department of Biology, Duke University, Durham, North Carolina 27708. - What can molecular data tell us about species delineation in the peatmosses (Sphagnum)?
Sphagnum is arguably the most controversial genus of mosses
with regard to species delineation. The four large sections of
Sphagnum are readily distinguishable, but within sections there
are complexes of closely related taxa that some bryologists recognize
as a single polymorphic species while others distinguish multiple,
more narrowly defined species within these complexes. Phylogenetic
architecture within sections of Sphagnum was investigated using
DNA sequences from the chloroplast and nuclear genomes. Although it is
still too early to make taxonomic decisions on the basis of molecular
data, evidence available to date suggests that such groups as the
S. capillifolium complex represent monophyletic groups but that
the "little" species within such complexes are often para-
or polyphyletic. These observations suggest that either the
"little" species within complexes are unnatural and are
based on convergent morphological features, or that these species are
so recently derived that gene coalescence predates speciation. On the
other hand, some Sphagnum species, including S. molle, S.
fuscum, and S. tenerum, are clearly distinct in terms of
DNA sequences. Across the genus, phylogenetic structure at the
population and species level is very heterogeneous. Populations in the
section Rigida, for example, are relatively distinct, as are
the two species of Rigida (S. compactum and S.
strictum). Molecular approaches to species delineation have not
reached maturity yet, but appear very promising.
Key words: molecular systematics, peatmosses, speciation, species concepts, Sphagnum