Molecules and morphology in South American stipeae (Poaceae)

Abstract

We conducted phylogenetic analyses of molecular data (ITS, trnH-psbA, trnC-trnL, and trnK-rps16) for 71 species of stipoid grasses. Of these species, 30 are native to South America, seven are native to Mexico and/or the southwestern United States, 15 to other parts of North America, 12 to Eurasia and/or the Mediterranean region, and seven to Australia. The outgroup was Glyceria declinata, a member of the Meliceae, a tribe that is in the same clade as and possibly sister to, the Stipeae. The purpose of the study was to evaluate alternative generic treatments of the South American Stipeae, all of which are based on morphological and anatomical information. Questions of particular interest were the merits of recognizing Amelichloa and of including Stipa subgg. Pappostipa and Ptilostipa in Jarava. Trees obtained from separate analyses of the ITS and cpDNA data were poorly resolved. The majority rule consensus tree obtained from the combined data provided strong support for the monophyly of only two currently recognized genera, Piptochaetium and Hesperostipa. There was strong support for a lineage comprising Amelichloa, Jarava s. str., most North American species of Achnatherum, and most samples of Nassella. Amelichloa was included within a poorly resolved Nassella clade that was sister to the Jarava clade. Austrostipa, with the exception of one sample, was monophyletic and sister to the poorly supported Achnatherum-Amelichloa-Nassella-Jarava clade. Stipa subg. Pappostipa formed a separate strongly supported clade if the North American samples of S. speciosa were excluded from consideration. None of the trees support including S. subg. Pappostipa in Jarava. For S. subg. Ptilostipa we obtained no ITS data and cpDNA data for only one species. The cpDNA data placed the species in a clade with two Nassella species.