136 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



This is Arizona's most important genus of forage grasses. Rothrock 

 grama (B. rothrockii) and sideoats grama (B. curtipendula) are some- 

 times cut for hay in the southeastern part of the State. Blue grama 

 (B. gracilis) is highly valued and often predominant in "short-grass" 

 areas north of the Mogollon Escarpment. When too heavily grazed 

 these areas are encroached upon by noxious weeds and grasses of lower 

 palatability. Three annual gramas furnish a large quantity of forage, 

 but this is of poorer quality and shorter duration than that produced 

 by the perennial species. Of these, sixweeks grama (B. barbata) and 

 needle grama (B. aristidoides) are abundant in the foothills and plains 

 of the southern counties, and mat grama (B. simplex) is important on 

 the northern plateaus. 



Key to the species 



1. Spikes deciduous, falling entire; spikelets not pectinate or obscurely so (2). 

 2. Plant annual; spikes very narrow, abruptly spreading above, the rachis 



sharp-pointed at base; spikelets appressed 10. B. aristidoides. 



2. Plants perennial; spikes relatively broad, the rachis not sharp-pointed at 

 base (3). 

 3. Spikes 20 to 40; spikelets appressed or somewhat spreading. 



15. B. CURTIPENDULA. 



3. Spikes fewer than 15 (4). 

 4. Second glume hairy (5) . 



5. Spikes 3 to 8, rhomboid, the margins of the rachis densely ciliate; 

 spikelets obscurely pectinate 11. B. chondrosioides. 



5. Spikes 10 to 13, triangular, the margins of the rachis not conspicu- 



ously ciliate; spikelets not pectinate 12. B. ELUDENS. 



4. Second glume glabrous (6). 



6. Base of the plant hard and rhizomatous; sheaths usually broad and 



conspicuous 13. B. radicosa. 



6. Base of the plant comparatively soft, not rhizomatous; sheaths 



inconspicuous 14. B. filiformis. 



1. Spikes persistent; spikelets pectinate (7). 

 7. Plants annual (8). 



8. Spike 1, ascending or spreading, curved 1. B. simplex. 



8. Spikes 4 to 7, finally spreading, straight (9). 



9. Second glume papillose-hispid on the keel; rachis papillose-hispid- 



ciliate 2. B. parryi. 



9. Second glume scabrous on the keel; rachis not ciliate. 3. B. barbata. 

 7. Plants perennial (10). 



10. Rachis produced beyond the spikelets, pointed; second glume tubercu- 

 late-hispid (11). 

 11. Culms glabrous 4. B. hirsuta. 



11. Culms retrorsely hirsute below the nodes 5. B. glandulosa. 



10. Rachis terminating in a spikelet, this often rudimentary; second glume 



glabrous, scabrous, or pubescent, sparsely papillose-pilose in B. 

 gracilis (12). 



12. Spikes normally 2, rarely 1 or 3; second glume sparsely papillose- 



pilose 6. B. GRACILIS. 



12. Spikes 3 to 8; second glume not at all papillose-pilose (13). 



13. Culms felty-pubescent, wiry, straggling, sparingly stoloniferous. 



7. B. ERIOPODA. 

 13. Culms glabrous, erect, cespitose, not stoloniferous (14). 



14. Culms branching; awns of the fertile lemma 2 to 3 mm. long; 



plant often appearing annual 8. B. rothrockii. 



14. Culms simple; awns of the fertile lemma about 5 mm. long. 



9. B. TRIFIDA. 



1. Bouteloua simplex Lag., Var. Cienc. 2 4 : 141. 1805. 



Bouteloua prostrata Lag., Gen. et Sp. Nov. 5. 1816. 



Apache, Coconino, and Yavapai Counties, up to 7,000 feet, dry 

 plains and open woods, August to September. Texas to Colorado, 

 Utah, Arizona, and Mexico. 



