446 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



Figure 946.— Distribution of 

 Aristida dichotoma. 



and more conspicuous blades, the looser panicles of larger spikelets, 

 the more unequal glumes, the longer second glume (about 1 cm long), 

 the longer smooth lemma (about 1 cm long) and central awn, and the 

 usually longer lateral awns; central awn about 1 cm long, the lateral 

 awns 2 to 4 mm long, o — Open dry ground, 

 Maryland to West Virginia; Florida; Illinois 

 to Wyoming and Oklahoma (fig. 948). 



11. Aristida oligantha Michx. Prairie 

 three- awn. (Fig. 949.) Annual, much 

 branched; culms 30 to 50 cm tall; blades flat or 

 loosely involute, usually not more than 1 mm 

 wide; panicle loose, 10 to 20 cm long; spikelets 

 short-pediceled the lower often in pairs ; glumes 

 about equal, 2 to 3 cm long, tapering into an awn, the first 3- to 5- 

 nerved; lemma about 2 cm long, the awns about equal, divergent, 4 

 to 7 cm long, somewhat spirally curved at base, o —Open dry 

 ground, Massachusetts to South 

 Dakota, south to Florida and Texas; 

 Oregon to Arizona (fig. 950). 



12. Aristida ramosissima Engelm. 

 (Fig. 951.) Annual, much branched; 

 culms 30 to 50 cm tall; blades flat or 

 involute, about 1 mm wide; panicle 

 narrow, 8 to 12 cm long; glumes 3- to 

 5-nerved, the first about 15 mm, the 

 second about 2 cm long, including an 

 awn 3 to 5 mm long; lemma about 

 2 cm long, tapering into a neck about 

 5 mm long; central awn with a semi- 

 circular bend or part of a coil at base, 

 15 to 20 mm long, spreading, the lat- 

 eral awns reduced or as much as 6 mm 

 long, rarely longer, o — Open sterile 

 soil, Indiana to Iowa, south to Tennes- 

 see, Louisiana, and Texas (fig. 952). 



13. Aristida longespica Poir. (Fig. 



953.) Annual, branched; culms 20 to 



40 cm tall; blades flat or involute, 



about 1 mm wide; panicles narrow, 



slender, the terminal 10 to 15 cm or 



even 20 cm long; glumes about equal, 



5 mm long; lemma 4 to 5 mm long; 



central awn sharply curved at base, spreading, 5 to 15 mm long, 



the lateral awns erect, one- third to half as long as the central, some- 

 times only 1 mm long, o (A. gracilis Ell.) 

 — Sterile or sandy soil, New Hampshire to 

 Michigan, south to Florida and Texas, espe- 

 cially on the Coastal Plain (fig. 954). In the 

 typical form the lateral awns are short; in 

 var. geniculates Fernald (A. geniculate Raf.) 

 the lateral awns are more than one-third as 

 long as the central one. 



14. Aristida adscensionis L. Sixweeks three-awn. (Fig. 955.) 

 Annual, branched at base, erect or spreading; culms 10 to 80 cm 



Figure 947.— Aristida curtissii, X 1. 

 (Waite, 111.) 



Figure 948.— Distribution of 

 Aristida curtissii. 



