North American Stipeae (Gramineae): Taxonomic changes and other comments

The generic treatment of North American Stipeae is substantially modified. Seven genera are recognized, Achnatherum, Piptatherum, Oryzopsis, PtUagroatis, Piptochaetium, Naaaella, and Hesperostipa, Only Hesperoatipa has not previously been recognized at the generic level. The characteristics of each genus are summarized anA. the 45 new combinations necessitated by this treatment presented. All species occurring in the continental U.S.A. and Canada are treated, plus a few of those occurring in northern Mexico. The largest genus, both globally and regionally, is AchnatheTum. HespeTostipa comprises four species, H. comata, H. spctf'tea, H. curtiseta, and H. neomexicana. The taxonomic changes at the specific level are 1) the description of a new species, A. perplexum, 2) modification of the limits of A. lobatum, A. occidentale, and A. coronatum, and 3) selection of a neotype for Stipa robusta (Vasey) Scribner.