<i>NASSELLA</i> (GRAMINEAE, STIPEAE): REVISED INTERPRETATION AND NOMENCLATURAL CHANGES

Summary The taxonomic history of Nassella Desv. is reviewed and its circumscription expanded to include all species of Stipeae with strongly overlapping lemma margins; lemma apices that are fused into a crown; paleas that are highly reduced, ecostate, and glabrous; long epiblasts; and lemma epidermes with very short fundamental cells having silicified cell walls. The expanded genus includes 79 species, almost all of which are South American. Piptochaetium and Stipa sect. Hesperostipa are suggested as the closest extant relatives. Synapomorphies of the three taxa are: brownish callus hairs; fused lemma apices; bulbous‐based lemma cilia; silicified lemma fundamental cells; and long epiblasts. A key to putatively monophyletic groups in American Stipeae and a synopsis of Nassella s.l., involving more than 60 new combinations, are presented. The transferred species include representatives from seven subgenera of Stipa L. described by Spegazzini.