MANUAL OF THE GRASSES OF THE UNITED STATES 463 



Creeping rhizomes present. Glumes unequal, awned; awns loosely twisted at base, 



the central a little longer, 18 to 24 mm. long 31. A. rhizomophora. 



Creeping rhizomes wanting (sometimes short ones in A. stricta). 



4a. First glume about half as long as the second (as much as two-thirds as long 

 in A. glauca). (Group Purpureae.) 

 Lemma tapering into a slender somewhat twisted beak 5 to 6 mm. long; awns 



1.5 to 2.5 cm. long, widely spreading 22. A. glauca. 



Lemma beakless or only short-beaked. 



Branches of the rather loose and nodding panicle slender and flexuous (see 

 also A. longiseta var. rariflora). 



Lemma about 1 cm. long; awns 3 to 5 cm. long 23. A. purpurea. 



Lemma 7 to 8 mm. long; awns about 2 cm. long.... 24. A. roemeriana. 

 Branches of the erect panicle stiff and appressed, or the lowermost some- 

 times somewhat flexuous. 

 Panicle mostly more than 15 cm. long, the branches several-flowered; 

 awns about 2 cm. long. Sheaths with a villous line across the collar. 



25. A. WRIGHTII. 

 Panicle mostly less than 15 cm. long, the branches few-flowered; awns 2 

 to several cm. long. 

 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. purpurascens. 



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, sometimes 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 (sometimes subinvolute in A. condensata). 



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.) u glumes 1-nerved; awns 



Reichenb. / ° -, 



nearly equal. 



Lemma articulate with the column of 1. Aristida desman tha Trin. and 



the awns, the latter finally decid- Rupr. (Fig. 672.) Annual; branching, 



