MANUAL OF THE GRASSES OF THE UNITED STATES 101 



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



Blades broad and short; lower panicle branches reflexed. 



Blades elongate; panicle branches ascending, . 14. P NERVOSA' 



4b. Lemmas pubescent. 



5a. Lemmas glabrous except for the web at the base. 



c , T 15. 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_ 14. P. NERVOSA 

 Lower sheaths glabrous (scaberulous in P. laxiflora): lemmas 

 webbed at base. 



Culms retrorsely scabrous 16. P. LAXIFLORA 



Culms glabrous. 



Lower panicle branches in a whorl of usually five; blades 



mostly shorter than the culm 17. P. PRATENSIS. 



Lower panicle branches usually in twos, spreading, spikelet- 

 bearing near the ends; blades about as long as the culm. 



18. P. CUSPIDATA. 

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



pubescent. 



Panicle contracted, the branches appressed; blades folded, firm and 

 stiff. Plains and alkali meadows at medium altitudes. 



19. P. ARIDA. 



Panicle open, the branches spreading. 



Plants mostly more than 50 cm tall; panicle narrow, 10 to 20 cm 

 long, the lower branches mostly in threes. 



20. P. GLAUCIFOLIA. 



Plants mostly less than 50 cm tall; panicle pyramidal, 5 to 10 cm 

 long, the lower branches mostly in twos. Alpine meadows. 



21. P. ARCTICA. 



3. Palustres 



la. Lemmas glabrous, or the keel sometimes pubescent. 

 Sheaths retrorsely scabrous. Culms decumbent and often rooting at base; 



keel of lemma glabrous or slightly pubescent 22. P. TRI VIALIS. 



Sheaths glabrous. 



Panicle narrow, drooping, the branches appressed or ascending. 



23. P. MARCIDA. 



Panicle very open, the few branches slender, naked below, spreading or 



drooping. 

 Lemmas villous on the keel; panicle branches mostly in fours or fives. 



24. P. ALSODES. 

 Lemmas glabrous on the keel; panicle branches mostly in twos or threes. 



Lemmas obtuse 25. P. LANGUIDA. 



Lemmas acute 26. P. SALTUENSIS. 



Ib. Lemmas pubescent on keel and marginal nerves. 



2a. Sheaths distinctly retrorse-scabrous (sometimes faintly so). Culms 

 usually stout, 40 to 120 cm tall; panicle usually large and open, mostly 



more than 15 cm long 27. P. OCCIDENTALS. 



2b. Sheaths glabrous or faintly scaberulous. 



3a. Lower panicle branches distinctly reflexed at maturity. 



Panicle oblong, erect, mostly more than 15 cm long, the branches several 



(usually more than 3) in a whorl. 29. P. SYLVESTRIS. 



Panicle nodding, mostly less than 15 cm long, the branches 1 to 3 together. 



30. P. REFLEXA. 



3b. Lower panicle branches not reflexed. 



4a. Panicle narrowly pyramidal, erect, 15 to 20 cm long. Lemmas 4 mm 

 long, pubescent on nerves and internerves; webbed at base; New 



Mexico 28. P. TRACYI. 



4b. Panicle broadly pyramidal, usually nodding. 



5a. Intermediate nerves of lemma distinct 31. P. WOLFII. 



5b. Intermediate nerves of lemma obscure. 



6a. Lower panicle branches in pairs, elongate, capillary, bearing a 

 few spikelets near the ends. 



