GENERA OF GRASSES OF THE UNITED STATES. 193 



Heterosteca Desv., Nouv. Bull. Soc. Philom. Paris 2: 188. 1810. Based on 

 //. juncifolia, which is Bouteloua heterostega (Trin.) Griffiths, of the West 

 Indies. 



Chondrosium Desv., Nouv. Bull. Soc. Philom. Paris 2 : 188. 1810. Based on 

 Chloris procumbens Durand (Bouteloua procumbens). 



Polyodon H. B. K., Nov. Gen. and Sp. 1 : 174, pi. 55. 1816. Based on a single 

 species, P. distichum H. B. K. 



Triaena H. B. K., Nov. Gen. and Sp. 1 : 178. 1816. A single species described, 

 T. racem<osa, which is Bouteloua triaena (Trin.) Scribn. 



Eutriana Trin., Fund. Agrost. 161. 1820. Trinius includes two species, E. 

 curtipendula and E. bromoides. The first is selected as the type. 



The species fall into two rather well marked divisions, those in 

 which the spikelets are crowded and pectinate and the spikes persist- 

 ent on the main axis, the florets falling, and those in which the 

 spikelets are less crowded, ascending rather than pectinate on the 

 rachis, and the spikes falling entire. Bouteloua gracilis and its 

 allies are examples of the first group and B. filiformis (Fourn.) 

 Griffiths and its allies, B. curtipendula and B. aristidoides of the sec- 

 ond. The genus is important, since many of the species are the 

 chief ingredient of the grazing lands of the Southwestern States. 



Bouteloua gracilis Lag. (B. oligostachya Torr.) (fig. 114) is 

 found on the Great Plains from Manitoba to Mexico and even south- 

 ward to South America. It is the blue grama of the ranchmen and, 

 along with buffalo grass (Bulbilis dactyloides} and curly mesquite 

 (Hilaria belangeri) , constitutes most of what is known in the Middle 

 West as "short-grass." Blue grama is a tufted perennial, with 

 numerous short leaves and a flower stalk about a foot high with 2 

 or 3 spikes about an inch long. These spikes, one at the end of the 

 stem and the other one or two a short distance below, turn with the 

 wind like weather vanes. An allied species, B. Mrsuta Lag., 

 called black grama, is found over about the same region, but is con- 

 fined chiefly to rocky hills. This species differs in having shorter, 

 niore fuzzy spikes and in the prolonged end of the rachis, which 

 forms a distinct point beyond the spikelets. 



Another widely distributed species is Bouteloua curtipendula 

 (Michx.) Torr. (B. racemosa Lag.) (fig. 115), called side-oats 

 grama. It extends farther east than the other species, being found 

 even as far as Connecticut. Side-oats grama is the tallest of the 

 species, sometimes as much as 3 feet, and is further distinguished 

 by the numerous (35 to 50) short, reflexed spikes. 



In Arizona and New Mexico other species become prominent. 

 Bouteloua eriopoda Torr., called here black grama and woolly-foot, 

 is a low creeping species with woolly stem. Bouteloua rothrockii 

 Vasey is the most important range grass in many parts of Arizona. 

 It grows about a foot high and has five or six spikes to each culm. 

 In B. texana S. Wats., of the Texas plains, the short triangular 

 spikes fall from the axis entire. 

 97769 19 Bull. 772 13 



