GENERA OF GRASSES OF THE UNITED STATES. 81 



30. SCLEROPOGON 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 Fourn., Bull. Soc. Bot. France 2 7 : 102, pi. 3, 4. 1880. Two species 

 Are proposed, L. multlflora and L. kar wins ky ana, 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 long- 

 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 



