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-3trnK 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