TATE, JENNIFER A.* AND BERYL B. SIMPSON. Section of Integrative Biology, University of Texas at Austin, Austin, TX 78712. - Towards a phylogeny of the genus Tarasa (Malvaceae): Evolution in the high Andes.
A phylogenetic approach is being used to investigate the evolution and
biogeographical history of the polyploid Andean genus Tarasa
(Malvaceae). Members of the genus are characterized by their blue or
purple flowers (sometimes white) displayed in axillary scorpioid
cymes, with apically aristate, completely dehiscent mericarps, and a
base chromosome number of x=5. The 30 species exhibit a complex
biogeographical pattern involving elevational separation of ploidy
levels in the Andes, endemism, and long distance disjunctions. The
polyploid species of the genus are particularly unusual in that all
are annuals and have reduced floral morphologies as compared to the
diploid species. A preliminary phylogeny was reconstructed using ITS
sequence data from species of Tarasa and other Andean and
lowland South American genera also traditionally placed in the
Sphaeralcea alliance. Our preliminary results indicate that the
tetraploid species of Tarasa form a monophyletic group but that
the genus may not be monophyletic. The placement of the closely
allied genera Sphaeralcea and Nototriche within the
Tarasa clade was particularly surprising. The relationship
among these three genera will be discussed with regard to morphology
and geographic distribution. The findings from the nuclear-based
phylogeny will be compared with a phylogeny inferred from a non-coding
chloroplast region.
Key words: Andes, biogeography, Malvaceae, phylogeny, polyploidy, Tarasa