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. eltjdens. 



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 bevond 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. Atherop6gon (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 subinvolute, 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. % — 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 subinvolute, 3 to 4 mm wide, scabrous; 



