Molecular phylogenetic analysis resolves Trisetum (Poaceae: Pooideae: Koeleriinae) polyphyletic: Evidence for a new genus, Sibirotrisetum and resurrection of Acrospelion

To investigate the evolutionary relationships among the species of Trisetum and other members of subtribe Koeleriinae, a phylogeny based on DNA sequences from four gene regions (ITS, rpl32-trnL spacer, rps16-trnK spacer, and rps16 intron) is presented. The analyses, including type species of all genera in Koeleriinae (Acrospelion, Avellinia, Cinnagrostis, Gaudinia, Koeleria, Leptophyllochloa, Limnodea, Peyritschia, Rostraria, Sphenopholis, Trisetaria, Trisetopsis, Trisetum), along with three outgroups, confirm previous indications of extensive polyphyly of Trisetum. We focus on the monophyletic Trisetum sect. Sibirica clade that we interpret here as a distinct genus, Sibirotrisetum gen. nov. We include a description of Sibirotrisetum with the following seven new combinations: Sibirotrisetum aeneum, S. bifidum, S. henryi, S. scitulum, S. sibiricum, S. sibiricum subsp. litorale, and S. turcicum; and a single new combination in Acrospelion: A. distichophyllum. Trisetum s.s. is limited to one, two or three species, pending further study.