| Summary: | Poa, with about 575 species, is the largest genus of grasses, and has diversified throughout temperate, boreal, and arctic regions, and similar habitats through the tropics. This new phylogenetic study of Poa based on analysis of restriction site data from PCR amplified regions of chloroplast DNA (trnT-trnF, trnF-trnV, trnV-rbcL, rbcL-ORF106, trnH-trnK) expands previous sampling in the genus to where 1/5 to 1/6 of the species have been characterized for chloroplast DNA types. A broad phylogenetic structure detected in a previous study using restriction site mapping of Poa chloroplast DNA gained additional and robust support. Accounting for extended intra- and extrageneric sampling, Poa remains monophyletic if Austrofestuca and Parodiochloa are included as sections within P. subg. Poa, and if Poa subg. Andinae is removed from the genus. Two new combinations are made: Poa sect. Austrofestuca and Poa sect. Parodiochloa. This new analysis supports the recognition of five major clades within Poa 1) ArcSyl, Poa subg. Arctopoa sects. Arctopoa and Aphydris, and P. subg. Poa sect. Sylvestres; 2) BAPO, P. subg. Poa sects. (Bolbophorum Alpinae) (Parodiochloa Ochlopoa); 3) SPOSTA, P. subg. Poa sects. (Secundae (Pandemos (Orienos Stenopoa Tichopoa Abbreviatae))); 4) PoM, P. subg. Poa sects. (Poa Macropoa); 5) HAMBADD, P. subg. Poa sects. (Homalopoa, Acutifolae, Brizoides, Madropoa, Austrofestuca, Dasypoa, Dioicopoa, and informal groups “Punapoa” and “Australopoa”). These clades diverge in the following arrangement from the outgroups: ArcSyl (BAPO (SPOSTA ((PoM) (HAMBADD))).
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