MANUAL OF THE GRASSES OF THE UNITED STATES 229 



5-nerved, 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 separating 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 slender, scabrous, spread- 

 ing 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 

 stoloniferous perennial, with short flexuous blades and narrow few- 

 flowered racemes or simple panicles, the staminate and pistillate 

 panicles strikingly different in appearance. Staminate and pistillate 

 panicles may occur on the same plant or rarely the two kinds of 

 spikelets may be found in the same panicle. It may be that the seed- 

 lings produce two kinds of branches, each kind then reproducing its 



Own sex. This should be investigated. Type 



species, Scleropogon brevifolius. Name from 

 Greek skleros, hard, and pogon, beard, alluding 

 to the hard awns. 



1. Scleropogon brevifolius Phil. BURRO GRASS 

 (Fig. 439.) Culms erect, 1 to 20 cm tall, tufted, 

 producing wiry stolons with internodes 5 to 

 15 cm long; leaves crowded at the base, the 

 blades flat, 1 to 2 mm wide, sharp-pointed; 

 racemes, excluding awns, 1 to 5 cm long; staminate spikelets 

 2 to 3 cm long; body of pistillate spikelets 2.5 to 3 cm long, 

 the awns 5 to 10 cm long, loosely twisted. 01 (S. karwinskyanus 

 Benth.) Semiarid plains and open valley lands, Texas to Colorado 

 and Arizona, south to central Mexico; Argentina (fig. 440). The ma- 

 ture pistillate spikelets break away and with their numerous long 

 spreading awns form " tumbleweeds " that are blown before the wind, 

 the pointed barbed callus readily penetrating clothing or wool, the 

 combined florets acting like the single floret of long-awned aristidas. 

 Spikelets rarely staminate below and pistillate above. On overstocked 

 ranges, where it tends to become established, it is useful in preventing 

 erosion. Often important as a range grass, especially when young. 



TRIBE 3. HORDEAE 



39. AGROPfRON Gaertn. WHEATGRASS 



Spikelets several-flowered, solitary (rarely in pairs), sessile, placed 

 flatwise at each joint of a continuous (rarely disarticulating) rachis, 

 the rachilla disarticulating above the glumes and between the florets ; 

 glumes equal, firm, several-nerved, rarely 2-nerved, 1-nerved, or 

 nerveless, usually shorter than the first lemma, acute or awned, rarely 

 obtuse or notched; lemmas convex on the back, rather firm, 5 to 

 7-nerved, acute or awned from the apex; palea about as long as the 

 lemma. Perennials (our species except Agropyron triticeum), often 

 with creeping rhizomes, with usually erect culms and green or purplish, 

 usually erect spikes. Type species, Agropyron triticeum Gaertn. 

 Name from Greek agrios, wild, and puros, wheat, the two original 

 species being weeds in wheat fields. 



Most of the species of Agropyron furnish forage and a few are among 

 the most valuable range grasses of the Western States. In the valleys 

 some species may grow in sufficient abundance to produce hay. 



