Molecular phylogeny reveals recent rapid diversification of Poa supersect. Homalopoa in the New World

GIUSSANI, LILIANA [1], GILLESPIE, LYNN [2], SCATAGLINI, AMALIA [1], NEGRITTO, MARIA [3], SORENG, ROBERT J [4].

Idaho

Congreso; Botany, new frontiers in Botany; 2014

ASPT

Poa subgenus Poa supersection Homalopoa includes c. 320 species distributed worldwide and represents the most recent large radiation within the genus. In South America Homalopoa includes c. 80 species that are morphological and reproductively diverse, including hermarphroditic, gynomonoecious, gynodioecious, dioecious, and pistillate-apomictic species. Here we use analyses of nrDNA ITS, ETS, and plastid trnT-trnL-trnF sequence data to examine phylogenetic structure, evolution of reproductive systems, and divergence dates in supersection Homalopoa with a focus on South American species. Although basal relationships in the Homalopoa clade are not resolved, five well-supported large subclades are recovered, of which three correspond to sects. Dioicopoa, Madropoa, and Australian Brizoides. Dioecism appears to have evolved independently at least twice within supersect. Homalopoa, in sects. Dioicopoa and Madropoa. The North American species Poa arachnifera is confirmed as a member of the exclusively dioecious South America sect. Dioicopoa. The informal Andean group ?Punapoa? primarily resolves as two separate clades, one corresponding to mostly dwarf pistillate-apomictic species, and the second to taller gynomonecious species. Apart from characterizing the dwarf ?Punapoa? clade, one pistillate species Poa wheeleri evolved independently in the dioecious sect. Madropoa. Gynomonoecism appears to have evolved multiple times in Homalopoa. Origin of the major Homalopoa lineages appears to have taken place in the Pliocene, while speciation within the lineages likely occurred primarily in the Pleistocene.