144 MISC. PUBLIC ATIOX 42 3, U. ST. DEPT. OF AGRICULTURE 



lemma sometimes enclosing a staminate flower; fertile lemma indurate, 

 typically obtuse. 



Bulb panicum (P. bulbosum),Vme-mesquite (P. obtusum), and switch- 

 grass (P. rirgatum) yield forage and are sometimes cut for hay. Vine- 

 mesquite is an excellent plant for controlling too rapid erosion in 

 gulleys, but is sometimes looked upon as a weed. The seeds of several 

 species were used for food by the Indians of Arizona. 



Key to the species 

 1. Plants annual (2). 



2. Fruit transversely rugose; spikelets obscurely arranged in spikelike racemes 

 (3). 

 3. Spikelets dark brown, strongly reticulate-veined, glabrous. 



1. P. FASCICTJLATUM. 



3. Spikelets green, reticulate-veined only at the apex, pubescent (4). 



4. Spikelets 3.5 to 3.8 mm. long; sheaths and blades glabrous to papillose- 

 hispid 2. P. ARIZOXICUftl. 



4. Spikelets 5 to 6 mm. long; sheaths and blades soft-pubescent. 



3. P. TEXANUM. 



2. Fruit smooth and shining (5) . 



5. First glume short, truncate 4. P. dichotomiflorum. 



5. First glume usually as much as half the length of the spikelet, acute or 

 acuminate (6). 

 6. Panicles usually more than half the height of the culm, the branches 



stiffly spreading 5. P. capillare. 



6. Panicles not more than one-third the height of the culm, the branches 

 ascending (7). 

 7. First glume subacute or blunt, about one-third the length of the 



spikelet 6. P. stramineum. 



7. First glume acuminate, usually more than half the length of the 

 spikelet (8). 



8. Spikelets 4 mm. long 7. P. pampixostjm. 



8. Spikelets not more than 3.3 mm. long 8. P. hirticaule. 



1. Plants perennial (9). 



9. Basal leaves distinctly different from those of the culm, forming a winter 

 rosette; culms at first simple, later becoming much branched (10). 

 10. Spikelets 3.2 to 3.3 mm. long, glabrous or very sparsely pubescent. 



11. P. SCRIBXERIAXUM. 



10. Spikelets 1.6 to 1.8 mm. long, pubescent; ligule of conspicuous hairs 4 to 

 5 mm. long (11). 

 11. Blades glabrous on the upper surface, with rather conspicuous firm 



white margins 9. P. texxesseexse. 



11. Blades pilose on the upper surface, sometimes near the base only. 



10. P. HUACHTJCAE. 



9. Basal leaves similar to those of the culm, not forming a winter rosette (12). 

 12. Plants cespitose; rhizomes and stolons wanting (13). 

 13. Fruit transversely rugose (14). 



14. Culms distinctly bulbous at base 12. P. bulbosum. 



14. Culms not bulbous 13. P. plenum. 



13. Fruit smooth (15). 



15. Spikelets 3 to 3.7 mm. long; leaves crowded toward base, the blades 



becoming curled or twisted with age 14. P. hallii. 



15. Spikelets 4 to 4.2 mm. long; leaves not crowded toward base, the 



blades not curled 15. P. lepidulum. 



12. Plants rhizomatous or with widely creeping stolons (16). 



16. Plants without rhizomes; first glume obtuse; fruit as long as the spike- 

 let; culms erect from a knotty crown, with long, widely spreading 

 stolons, the nodes of the stolons densely bearded. 



18. P. OBTUSTJM. 

 16. Plants rhizomatous; first glume acute; fruit much shorter than the 

 spikelet (17). 

 17. Spikelets densely villous, 6 to 7 mm. long; nodes densely bearded. 



16. P. URVILLEAXUM. 



17. Spikelets glabrous, 3.5 to 5 mm. long; nodes glabrous. 



17. P. VIRGATTJM. 



