Taxonomic Revision of Trisetum section Acrospelion (Poaceae: Pooideae: Aveninae) from Eurasia

Ataxonomic revision of Trisetum sect. Acrospelion is presented. We include descriptions and synonyms of each taxon from a study of 670 vouchers from 45 herbaria. Detailed morphometric descriptions, illustrations, distribution maps, identification key, and habitat data are given for each taxon. Twelve names are lectotypified: Aira halleri Honck., Avena argentea Willd., Avena brevifolia Host, Avena daenensis Boiss., Avena distichophylla Vill., Trisetum argenteum var. parviflorum Parl., Trisetum cavanillesianum Borja & Font Quer, Trisetum distichophyllum subsp. delphinense Beauverd, Trisetum macrotrichum Hack., Trisetum rigidum var. molle Somm. & Levier, Trisetum rigidum var. ovale Somm. & Levier, and Trisetum teberdense var. brevifolium Kharadze. We recognize seven species of Trisetum into the section, which is endemic to Eurasia: T. argenteum, T. buschianum Seredin, T. distichophyllum (Vill.) P. Beauv., T. macrotrichum, T. rigidum (M. Bieb.) Roem. & Schult., T. tamonanteae Marrero Rodr. & S. Scholz, and T. velutinum Boiss. Morphometric variation of the main characters is shown by box plots. The highest diversity is located in the Caucasian Mountains and the Alps, where two species were found in each area. Additionally, one species is endemic to the Canary Islands, a second to southeastern Spain, and a third to the Carpathian Mountains. In contrast with some regional treatments, T. persicum Chrtek is considered a synonym of T. rigidum (M. Bieb.) Roem. & Schult., and T. cavanillesianum Borja & Font Quer a synonym of T. velutinum Boiss. Trisetum rigidum subsp. teberdense (Litv.) Tzvelev and T. buschianum subsp. transcaucasicum (Seredin) Mosul. are recognized as subspecies. Vegetative propagation has been observed for the first time in specimens of T. rigidum and T. velutinum.