THERRIEN, JAMES P.* AND CHRISTOPHER H. HAUFLER. Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045. - Phylogeny and biogeography of Selaginella subg. Tetragonostachys based on nuclear ribosomal ITS sequence data.
Selaginella subg. Tetragonostachys is a group of ca. 50
widely distributed species that exhibit a number of putative
adaptations to xeric environments. Morphologically, the subgenus
includes taxa with thickened, isophyllous microphylls, tetrastichous
sporophylls, and in several species, the presence of vessels.
Previous phylogenetic analyses based on rbcL sequence data strongly
supported the monophyly of this subgenus, but failed to adequately
resolve relationships within the group. To address open questions of
phylogenetic relationships, nuclear ribosomal internally transcribed
spacer (nrITS) sequences were obtained from 44 ingroup taxa and 6
outgroups. Maximum parsimony analysis of the data yielded several
well supported clades. The resulting tree topology exhibits patterns
that are consistent with classic Tertiary relictual distributions.
There is strong support for a clade comprised of taxa from southern
Africa, Madagascar, and India - land masses previously united in a
larger assemblage. Further vicariant relationships include an eastern
US, western US, Asian clade, again with strong bootstrap support.
Moderate support is also obtained for a clade of species within
section Arenicolae, comprised of taxa distributed in the
southwestern US, southeastern US, and northern Africa. In addition,
several of the clades correspond well with morphological characters
traditionally considered indicative of sister group relationships.
These include such features as red pigmented microphylls, readily
fragmenting stems, dimorphic sporophylls, and the prostrate, incurling
habit. The overall pattern from the nrITS phylogeny suggests that
speciation in S. subg. Tetragonostachys may be
attributed primarily to vicariant events, rather than to long distance
Key words: ITS, Selaginella, Tertiary relict, vicariance