GENERA OF GRASSES OF THE UNITED STATES. 
193 
Heterosteca Desw, Nouv. Bull. Soc. Philom. Paris 2: 188. 1810. Based on 
][. jundfolia, which is Bouteloua heterosiega (Trin.) Griffiths, of the West 
Indies. 
Chondrosium Desw, 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. racemosa, which is Bouteloua triaena (Trin.) Scribn. 
Eutriana Trin., Fund. Agrost. 161. 1820. Trinius includes two species, E. 
curtipencUtla 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, 
more 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 grow 7 s 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 
