GENERA OF GRASSES OF THE UNITED STATES. 
81 
30. ScLERorocoN Philippi. 
Plants dioecious. Staminate spikelets several-flowered, pale, the 
rachilla not disarticulating; glumes about equal, a perceptible inter- 
node between, membranaceous, long-acuminate, 1-nerved or obscurely 
3-nerved, nearly as long as the first lemma; lemmas similar to the 
glumes, somewhat distant on the rachilla, 3-nerved or obscurely 5- 
nerved, the apex mucronate; palea obtuse, shorter than the lemma. 
Pistillate spikelets several-flowered, the upper florets reduced to 
awns, the rachilla disarticulating above the glumes but not separat- 
ing between the florets or only tardily so; glumes acuminate, 3- 
nerved, with a few fine additional nerves, the first about half as long 
as the second; lemmas narrow, 3-nerved, the nerves extending into 3 
slender, scabrous, spreading awns, the florets falling together forming 
a cylindric many-awned fruit, the lowest floret with a sharp-bearded 
callus as in Aristida ; palea narrow, the two nerves near the margin, 
produced into short awns. 
A perennial stoloniferous grass, with short flexuous blades and 
narrow few-flowered racemes or simple panicles, the staminate and 
pistillate strikingly different in appearance. Species one; Chile to 
southwestern United States. 
Type species: Scleropogon brevifolius Philippi. 
Scleropogon Philippi, Anal. Univ. Chile 36: 205. 1870. Only one species de- 
scribed. 
Lesourdia Foura, Bull. Soc. Bot. France 27: 102, pi. 3, 4. 1880. Two species 
Are proposed, L. multiflora and L. karwinskyana, both referable to the same 
species, Scleropogon brevifolius. 
This species (fig. 39) is found on semiarid plains and open valley 
lands from southern Colorado to Texas and Arizona and southward. 
The mature pistillate spikelets break away and with their numer- 
ous long spreading awns form " tumbleweeds " that are blown before 
the wind. The pointed barbed callus readily penetrates clothing or 
wool, the combined florets acting like the single floret of the lojig- 
awned aristidas. As a forage grass, this is inferior to grama ; but on 
overstocked ranges, where it tends to become established, it is use- 
ful in preventing erosion. It is called burro grass. 
31. Cottea Kunth. 
Spikelets several-flowered, the uppermost reduced, the rachilla dis- 
articulating above the glumes and between the florets; glumes two, 
about equal, nearly equaling the lower lemma, with several parallel 
nerves ; lemmas rounded on the back, villous below, prominently 9 to 11 
nerved, the nerves extending partly into awns of irregular size and 
partly into awned teeth ; palea awnless, a little longer than the body 
of the lemma. 
97769°— 19— Bull. 772 6 
