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



Spikes fewer, awns conspicuous. 

 Glumes pubescent. 



Spikes rhomboid-oblong, as much as 2 cm long, the spikelets somewhat 



pectinately arranged 6. B. CHONDROSIOIDES. 



Spikes cuneate-triangular, about 1 cm long (including the awns), the 



spikelets appressed, not pectinately arranged. 



Culms 20 to 30 cm tall; leaves crowded at base; spikes mostly 6 to 8. 



4. B. RIGIDISETA. 

 Culms mostly 30 to 50 cm tall, leafy throughout; spikes mostly more 



than 10 5. B. ELUDENS. 



Glumes glabrous or scabrous, not pubescent. 



Base of plants hard, rhizomatous; culms simple; spikes 2 to 3 cm long. 



7. B. RADICOSA. 



Base of plants not rhizomatous; culms branching; spikes usually about 1.5 

 cm, sometimes 2 cm, long 8. B. FILIFORMIS. 



Section 2. Chondrosium 



Plants annual (see also B. rothrockii) ; densely tufted, spreading. 



Spike 1 9. B. SIMPLEX. 



Spikes 2 or more. 



Rachis papillose-pilose 11. B. PARRYI. 



Rachis not pilose 10. B. BARBATA. 



Plants perennial. 



Plants decumbent or stoloniferous; culms white-lanate 16. B. ERIOPODA. 



Plants erect or nearly so; culms not lanate, tufted. 

 Spikes normally 2, sometimes 1 or 3. 



Rachis prolonged beyond the spikelets as a naked point; glumes tuber- 



culate 13. B. HIRSTJTA. 



Rachis not prolonged; glumes not tuberculate (slightly so in B. gracilis). 



Culms herbaceous, the base not woody 14. B. GRACILIS. 



Culms woody and perennial at base__ 15. B. BREVISETA. 



Spikes normally 4 or more (see also B. gracilis var. stricta). 



Culms 25 to 50 cm tall; awn 1 to 2 mm long; glumes scabrous; spikes 



spreading 12. B. ROTHROCKII. 



Culms 10 to 20 cm tall; awn about 5 mm long; glumes glabrous; spikes 

 usually appressed 17. B. TRIFIDA. 



SECTION 1. ATHEROp6aoN (Muhl.) Endl. 



Spikes deciduous from the main rachis; spikelets not pectinately 

 arranged (somewhat so in B. chondrosioides) . (Atheropogon 

 Muhl. based on A. apludoides Muhl. (Bouteloua curtipendula).) 



1. Bouteloua aristidoides (H.B.K.) Griseb. NEEDLE GRAMA. (Fig. 

 1080.) Annual, erect or spreading, branching; culms slender, 10 

 to 30 cm tall; blades small and few, in vigorous plants as much as 15 

 cm long; spikes mostly 8 to 14 on a slender axis, reflexed, readily 

 falling, the base of the rachis forming a sharp, bearded point ; spikelets 

 2 to 4, narrow, appressed; rudiment of 3 scabrous awns about 5 mm 

 long, exceeding the fertile floret, o (Triathera aristidoides Nash.) 

 Mesas, deserts, and foothills in open ground, Texas to southern Cali- 

 fornia and northern Mexico; Argentina (fig. 1081). 



2. Bouteloua uniflora Vasey. (Fig. 1082.) Resembles slender 

 forms of B. curtipendula, culms slender, wiry, sometimes with slender 

 stolons, the slender blades subin volute, the spikes 8 to 9 mm long, 

 with 1 or 2 spikelets, the scabrous rachis mostly longer than the first 

 glume ; lemma awnless ; rudiment reduced to a single awn appressed 

 to the back of the palea. 91 Rocky hills and valleys, central and 

 western Texas. 



3. Bouteloua curtipendula (Michx.) Torr. SIDE-OATS GRAMA. 

 (Fig. 1083.) Perennial, with scaly rhizomes; culms erect, tufted, 50 

 to 80 cm tall; blades flat or subin volute, 3 to 4 mm wide, scabrous; 



