Format: ORAL

Joseph Charboneau1

1 Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA

With more than 3,000 recognized species, Astragalus L. (Fabaceae) is possibly the most species-rich genus of seed plants. With limited exceptions, the species recognized two decades ago have still been found to be part of one large Astragalus s.s. clade after subsequent phylogenies using small and large numbers of loci. These phylogenies have been relatively successful at identifying major clades within the genus especially for Old World species, where about 5/6 of the species richness of the genus is found. However, the phylogeny of the New World clade (informally called Neo-Astragalus) has proven more difficult to resolve. Neo-Astragalus has about 400 species in North America and 100+ species in South America that all have chromosome numbers in an aneuploid series (n = 11, 12, 13, 14, 15), in contrast to the euploid chromosome numbers predominant in the Old World (n = 8, 16). I will speak about the origin of the aneuploid series and chromosome number evolution in Neo-Astragalus as well as the paralogy that hinders phylogenetic inference within the clade. In addition to the variable structure of Neo-Astragalus nuclear genomes, plastid genomes in the clade have also undergone numerous rearrangements, some of which are shared by multiple species through homology and others shared through homoplasy. I will also examine rates of homoplasy in morphological characters within Neo-Astragalus and Astragalus as a whole and discuss how this may have influenced the number of species assigned to the genus.