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



is probably the most important forage grass of the lower elevations 

 in California; P. gracillima and P. ampla are mostly in the North- 

 western States; P. arida is the most valuable bluegrass of the Plains. 

 P. bigelovii, an annual, is important in the Southwestern States. 

 P. macrantha and P. confirm are native • sandbinders of the sand 

 dunes on the coast of Washington and Oregon, but are not cultivated. 



Spikelets little compressed, narrow, much longer than wide, the lemmas convex on 

 the back, the keels obscure, the marginal and intermediate nerves usually- 

 faint. All bunchgrasses. 

 Lemmas crisp-puberulent on the back toward the base (the pubescence some- 

 times obscure or only at the very base) 6. Scabrellae. 



Lemmas glabrous or minutely scabrous, but not crisp-puberulent. 



7. Nevadenses. 

 Spikelets distinctly compressed, the glumes and lemmas keeled. 



Plants annual 1 . Annuae. 



Plants perennial. 



Creeping rhizomes present 2. Pratenses. 



Creeping rhizomes wanting. 



Lemmas webbed at base 3. Palttstres. 



Lemmas not webbed at base (sometimes sparsely webbed in P. laxa and 

 P. pattersoni). 

 Lemmas pubescent on the keel or marginal nerves or both, sometimes 



pubescent also on the internerves 4. Alpinae. 



Lemmas glabrous (minutely pubescent at base in P. unilateralis) . 



5. Epiles. 

 1. Annuae 



Lemmas glabrous, except the scabrous keel, webbed at base. Sheaths glabrous. 



1. P. BOLANDERI. 



Lemmas pubescent. 



Lemmas pubescent on the back especially toward the base, but not distinctly 

 villous on the keel and nerves, slightly webbed at base. Sheaths usually 



scabrous; panicle open 2. P. howellii. 



Lemmas pubescent on the nerves, sometimes also on the internerves. 



Panicle narrow, contracted, usually interrupted; sheaths scabrous. Lemmas 



webbed, pubescent on the internerves below 3. P. bigelovii. 



Panicle oblong or pyramidal, the branches spreading; sheaths glabrous. ( 

 Lemmas with webby hairs at base, distinctly 3-nerved, the intermediate 



nerves obscure; anthers 0.1 to 0.2 mm long 4. P. chapmaniana. 



Lemmas not webbed at base, distinctly 5-nerved; anthers 0.5 tol mm long. 



5. P. ANNUA. 



2. Pratenses 



la. Culms strongly flattened, 2-edged 6. P. compressa. 



lb. Culms terete or slightly flattened, not 2-edged. 

 2a. Plants dioecious. 



Panicle oblong, the two sexes unlike in appearance, the pistillate spikelets 

 woolly, the staminate glabrous or nearly so. Plains of Texas. 



7. P. ARACHNIFERA. 



Panicle oblong or ovoid, the two sexes similar. Seacoast, California and 



northward. 



Glumes and lemmas about 8 mm long 8. P. macrantha. 



Glumes and lemmas not more than 6 mm long. 



Panicle densely ovoid; lemmas 6 mm long, slightly villous below. 



9. P. DOUGLASII. 



Panicle somewhat open; lemmas 3 mm long, scaberulous. 



10. P. CONFINIS. 

 2b. Plants not dioecious, the florets perfect. 



3a. Blades involute. Glumes and lemmas 4 to 5 mm long. 



11. P. RHIZOMATA. 



3b. Blades flat or folded. 



4a. Lemmas not pubescent nor webbed. 



Panicle almost spikelike, erect; glumes 2 mm long. 



12. P. ATROPURPUREA. 



