Taxonomic notes on the dwarf bluegrasses (Poa L., Poaceae) of section Stenopoa in Pan-Himalayas

The dwarf forms of Stenopoa (height 5-15 cm) which are common in alpine belt of the Pan-Himalayas, represent one of the most problematic groups in the genus. Ten dwarf species of Stenopoa have been recorded for the area under consideration: P. attenuata Trin, P.glauca Vahl, P. litvinoviana Ovcz., P. albertii Regel, P. koelzii Bor, P. lahulensis Bor, P. poophagorum Bor, P. arnoldii Melderis, P. mustangensis Rajb., and P. roemeri Bor. At least 6 other taxa have been mentioned as synonyms of these species. Comparative examination of many specimens of this group using a morphogeographic approach supports recognition of 10 species, which belong to 3 species aggregates: aggr. P. attenuata, aggr. P. glauca and aggr. P. albertii. Taxa in aggr. P. albertii are thought to have originated from hybridization between species of aggr. P. attenuata and aggr. P. glauca. Our research leads us to recommend recognizing P. roemeri, P. koelzii, P. mustangensis, P. rangkulensis Ovcz., P. scabriculmis N.R. Cui, P. tshuensis (Serg.) Olonova and P. indattenuata Keng as species; three of them have been recorded from the Pan-Himalayas. Poa koelzii is included in aggr. P. attenuata because of its similarity to that species. A key for identifying the taxa is presented. One new combination, Poa scabriculmis subsp. kunlunensis (N.R. Cui) Olonova, is presented.