MANUAL OF THE GRASSES OF THE UNITED STATES 441 



Lemma gradually narrowed above, scaberulous on the upper 

 half; leaves mostly in a short curly cluster at the base 



of the plant 27. A. fendleriana. 



Lemma scarcely narrowed above, scaberulous only at the 



tip; leaves not conspicuously basaL 26. A. longiseta. 



4b. First glume more than half as long as the second. (Usually the 



glumes about equal or the first sometimes a little longer.) 



Sheaths lanate-pubescent. Panicle branched, somewhat spreading; 



central awn 1.5 to 2.5 cm long, spreading or reflexed from a 



curved base 28. A. lanosa. 



Sheaths not lanate-pubescent. 



Column of awn at maturity 3 to 5 mm long, distinctly twisted. 



29. A. ARIZONICA. 



Column of awn less than 3 mm long, or if so long, not twisted. 

 Blades villous on upper surface near base, involute. 



30. A. STRICTA. 

 Blades not involute and villous at base. 



Awns at maturity about equally divergent, sometimes 

 slightly twisted but not spirally contorted at base. 

 Lemma about 7 mm long; awns horizontally spreading; 

 panicle usually more than 20 cm long. 



32. A. PTTRPTTRASCENS. 



Lemma 10 to 12 mm long; awns somewhat spreading but 

 scarcely horizontal; panicle mostly 10 to 15 cm long. 



33. A. PARISHII. 

 Awns at maturity unequally divergent or spirally contorted 

 at base. 

 Awns not spirally contorted at base; central awn more 

 spreading than the others, curved at base, some- 

 times reflexed. 

 Lateral awns erect, two-thirds to three-fourths as long 

 as the central. 



Glumes about 12 mm long 34. A. affinis. 



Glumes about 6 mm long 35. A. virgata. 



Lateral awns spreading or reflexed. Panicles nearly 

 simple. 

 Glumes 6 to 7 mm long; spikelets mostly in pairs. 



36. A. SIMPLICIFLORA. 



Glumes about 1 cm long; spikelets solitary. 



37. A. MOHRII. 

 Awns spirally contorted at base, spreading. 

 Blades flat. 



Panicle slender, the branches short, rather distant, 



few-flowered 38. A. tenuispica. 



Panicle rather thick, the branches as much as 10 cm 

 long, rather densely many-flowered. 



39. A. CONDENSATA. 



Blades involute 40. A. gyrans. 



Section 1. Arthratherum (Beauv.) Reichenb. 



Lemma articulate with the column of the awns, the latter finally- 

 deciduous; glumes 1-nerved; awns nearly equal. 

 1. Aristida desmantha Trin. and Rupr. (Fig. 934.) Annual; 

 branching, as much as 80 cm tall ; sheaths often woolly ; blades folded 

 or involute, 2 to 3 mm wide; panicle as much as 20 cm long, the 

 branches stiffly ascending, very scabrous, bearing 1 to few spikelets; 

 glumes slightly unequal, the body about 1 cm long, tapering into an 

 awn about half as long; lemma 7 to 8 mm long, glabrous below, some- 

 what laterally compressed and slightly twisted at summit, the densely 

 pubescent callus about 2 mm long; awns 2 to 2.5 cm long, united for 

 1 to 2 mm, the bases curved in a semicircular somewhat contorted 

 bend, the upper part thus usually deflexed. O —Open sandy soil 

 or sandy woods, Illinois, Nebraska, and Texas. 



