In 1986 Clayton and Renvoize (Kew Bull., Addit. Ser. 13: 1-389) assembled 16 genera into the Boutelouinae, one of their four subtribes in tribe Cynodonteae (Gramineae: Chloridoideae). However, evidence we have gathered from morphology (including lemma micromorphology), leaf blade transverse anatomy, cytology, and nuclear and chloroplast DNA sequences indicates that the subtribe, and indeed the tribe, is polyphyletic. Aegopogon and Schaffnerella appear closely related to genera in tribe Eragrostideae--Pereilema and Lycurus, respectively. The affinities of Melanocenchris and Neobouteloua remain uncertain, as is the case for the clade comprised of the sister taxa Hilaria and Pleuraphis (often treated as a single genus, as by Clayton and Renvoize). The remaining 12 Boutelouinae genera form a monophyletic group, but the largest genera--Bouteloua s.s. and Chondrosium--are not monophyletic. Considering our much-improved knowledge of relationships, the features in common to the 12 genera, and the practical issue of identification, we advocate that the group be treated as a single genus (Bouteloua s.l.). The many generic synonyms are testament to the wide range of variation in inflorescence form--including sexual dimorphism and branch persistence/abscission--displayed by Bouteloua. The evidence shows that some architectures have evolved in parallel, notably the Chondrosium-like staminate inflorescence of species scattered in several lineages. The long and erroneous affiliation of Aegopogon with Bouteloua, especially the Cathestecum group of species, can be owed to homoplasy. Remarkable is the convergence in inflorescence form between Aegopogon and the Cathestecum group: spikelets three per branch, the lateral two reduced; branches short, pendulous, and deciduous; lemma 3-awned. Although macromorphology has generally served us well in the classification of grasses and other plants, other sources of data are necessary to detect cases of homoplasy and to ensure that the units of classification best reflect phylogeny.

Key words: Aegopogon, Bouteloua, Boutelouinae, Chloridoideae, Chondrosium, Schaffnerella