TATE, JENNIFER A.* and BERYL B. SIMPSON. University of Texas at Austin, Section of Integrative Biology, Austin, Texas 78712. - Double trouble: Multiple origins of polyploidy in Tarasa(Malvaceae).
A molecular phylogenetic analysis of the Andean genus Tarasa
(Malvaceae) and related genera has yielded unexpected results
regarding generic boundaries, the origins of polyploidy within the
genus, and the morphological attributes of the polyploid taxa. As
currently circumscribed, the 30 species of Tarasa are
morphologically characterized by their blue or purple flowers (but
sometimes white) displayed in axillary scorpioid cymes, with apically
aristate, completely dehiscent mericarps, and a base chromosome number
of x=5. Most species are found at high elevations (2000-4200 m) from
central Peru to southern Chile and adjacent Argentina, with two
species disjunct in central Mexico. Interestingly, the polyploid
species (all tetraploid) of Tarasa occupy the highest elevation
habitats in the Andes. Further, the tetraploids are unusual in that
they are all annuals and have reduced floral morphologies as compared
to the diploid species. We used nuclear (ITS) and chloroplast
(psbA-trnH and trnT-trnL spacers,
matK-3’trnK intron) sequence data to reconstruct
independent phylogenies to test monophyly of the genus, determine its
sister taxon, and investigate the origin of the polyploid species.
Both the nuclear and chloroplast phylogenies do not support monophyly
of Tarasa as currently circumscribed. The high Andean genus
Nototriche and the North/South American disjunct genus
Sphaeralcea are placed within the Tarasa clade. The
sister taxon to this clade is equivocal. Lastly, the polyploid species
of Tarasa do not form a monophyletic clade and thus have been
generated multiple times. This finding is quite intriguing and
suggests that there has been morphological convergence toward reduced
floral features (including smaller pollen) of the high altitude
polyploid taxa.
Key words: Andes, biogeography, Malvaceae, phylogeny, polyploidy, Tarasa