A new species of Bouteloua, B. warnockii, is described from plants of western Texas, southern New Mexico, and northern Mexico. This grass has been confused with B. curtipendula (Michx.) Torr. with which it commonly is associated, and appears to be one of the ancestral types from which the latter has been derived. Bouteloua warnockii shows closest affinities to the relatively rare Caribbean species, B. vaneedenii Pilg. The type plant of the new taxon had a chromosome number of 2n--25 and another plant of the same population had 2n--22 chromosomes. Investigation of the Bouteloua curtipendula (Michx.) Torr. "species complex" has disclosed the presence of an undescribed Bouteloua in southwestern U. S. and northern Mexico. Plants of this taxon have been collected on limestone sites at several localities. Although at first believed to be markedly different from all other species of Bouteloua, this taxon has been determined to be close to the relatively rare B. vaneedenii Pilg. of the Caribbean area. Bouteloua vaneedenii appar- ently is known only from Anguilla, Leeward Islands (the type local- ity), and the province of Camaguey, Cuba (Griffiths, 1912; Hitch- cock, 1936). A report of the presence of B. vaneedenii in Venezuela (Swallen, 1939) apparently was based on a fragmentary specimen in the U. S. National Museum from Aragua (H. Pittier 11338) that has been examined and tentatively identified by the writers as B. disticha (H.B.K.) Benth. Three sheets of a Cuban collection (E. L. Eckman, Oct. 19, 1922) have been obtained on loan from the U. S. National Museum. These specimens show a remarkable similarity to those of the Southwest and the labels on the Cuban collections indicate that the two taxa occupy similar "limy" sites. The labels on two sheets bear the notation "in dry limestone littoral rocks" and the third sheet bears a more recent inscription "on miocene limestone." Bouteloua warnockii sp. nov. Dense caespitosa, culmi graciles rigide erecti 20-30 (-50) cm. alti. Foliorum laminae 1.0-2.5 mm. latae, 5-15 (-25) cm. longae, rigide erectae vel curvescentes, attenuatae, siccando