MANUAL OF THE GRASSES OF THE UNITED STATES 101 



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 to 1 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. 



Panicle pale, narrow, linear; lemmas scabrous; leaves crowded toward the base, 

 the blades very firm, conduplicate, pungent, curved. Lower sheaths fibrous. 



12. P. FIBRATA. 



Panicle tinged with purple, oblong; lemmas glabrous; leaves not crowded toward 

 the base, the blades flat or sometimes folded, straight, erect. 



13. P. ATROPURPUREA. 



Panicle open, nodding; glumes 3 to 4 mm. long. 



Blades broad and short; lower panicle branches reflexed 14. P. curta. 



Blades elongate; panicle branches ascending 15. P. nervosa. 



4b. Lemmas pubescent. 



5a. Lemmas glabrous except for the web at base 16. P. kelloggii. 



5b. Lemmas pubescent on the nerves or back, sometimes also webbed at base. 

 6a. Internerves glabrous, the keel and marginal nerves pubescent. 



Lower sheaths retrorsely pubescent, purplish; lemmas pubescent on keel and 



marginal nerves, not webbed 15. P. nervosa. 



Lower sheaths glabrous (scaberulous in P. laxi flora) ; lemmas webbed at base. 



Culms retrorsely scabrous 17. P. laxiflora. 



Culms glabrous. 



Lower panicle branches in a whorl of usually 5 ; blades mostly shorter than 



the culm 18. P. pratensis. 



Lower panicle branches usually in twos, spreading, spikelet-bearing near 



the ends; blades about as long as the culm 19. P. cuspidata. 



6b. Internerves pubescent near base, the keel and marginal nerves pubescent. 

 Panicle contracted, the branches ascending or appressed (sometimes open in 

 P. glaum 'folia). 

 First glume 2.5 to 3 mm. long, 1-nerved; first floret about 3 mm. long; 

 anthers 1.5 mm. long. Plains and alkali meadows at medium altitudes. 



20. P. ARIDA. 

 First glume 4 to 5 mm. long, 3-nerved; first floret 5 mm. long; anthers 2.5 



mm. long; spikelets mostly shining 21. P. glaucifolia. 



Panicle open, the branches spreading. 



Blades broad and short; lower panicle branches reflexed-.. 14. P. curta. 

 Blades 2 to 3 mm. wide; panicle pyramidal, the lower branches horizontal 



22. P. ARCTICA. 



