ANDREASEN, KATARINA* AND BRUCE G. BALDWIN. Jepson Herbarium and Department of Integrative Biology, University of California, Berkeley, CA 94720. - Phylogeny, unequal evolutionary rates, and biogeography in the western North American genus Sidalcea (Malvaceae).
Results of phylogenetic analyses of 18S-26S nuclear ribosomal DNA ITS
(Internal Transcribed Spacer) and ETS (External Transcribed Spacer)
sequences lead us to reject the previously suggested hypothesis of
monophyly for the annual species of Sidalcea (Malvaceae), a
western North American genus comprising ca. 25 species of annuals and
perennials. Based on the rDNA data, we conclude that the annual habit
arose at least three times, probably as an adaptation to seasonally
dry habitats. Among the perennials, S. oregana and S.
malviflora are the most heterogeneous species (with numerous
subspecific taxa) and each appears to be polyphyletic. Comparisons of
evolutionary rates between perennial and annual lineages in
Sidalcea establish that both ITS and ETS have evolved
significantly faster in the annuals than in the perennials. Roush's
(1931) hypothesis that the perennial species S. hickmanii and
S. malachroides represent basally divergent groups within
Sidalcea is upheld by our rDNA trees (although S. stipularis,
discovered subsequent to Roush's study, represents an additional
basally divergent lineage). Roush's (1931) suggestion that the genus
spread northward from Mexico along two major routes (through the Rocky
Mountains and the Sierra Nevada foothills) is not congruent with our
results. Of ca. 20 rare or endangered taxa in Sidalcea, those
corresponding to basally divergent lineages (i.e., S.
hickmanii, S. keckii, S. malachroides, and S.
stipularis) are well diagnosed by rDNA mutations. Others, e.g.,
the endangered S. nelsoniana (in the S. oregana clade),
cannot be distinguished from more common, closely related taxa using
ITS and ETS sequences.
Key words: evolutionary rates, Malvaceae, nuclear ribosomal DNA, phylogeny, Sidalcea