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



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 23. P. trivialis. 



Sheaths glabrous. 



Panicle narrow, drooping, the branches appressed or ascending 24. P. marctda. 



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

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



25. P. ALSODES. 

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



Lemmas obtuse 26. P. languida. 



Lemmas acute 27. P. saltuexsis. 



lb. 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. 



28. P. OCCIDENTALIS. 



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 _ 30. P. sylvestris. 



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



31. 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. 



29. P. TRACYI. 



4b. Panicle broadly pyramidal, usually nodding. 



5a. Intermediate nerves of lemma distinct 32. P. wolfii. 



5b. Intermediate nerves of lemma obscure (distinct in P. leptocoma). 



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

 near the ends. 

 Spikelets rather broad, the rachilla joints short, hidden by the florets; sheaths 

 smooth; culms in dense tufts; alpine rocky slopes. 



33. P. PAUCISPICULA. 



Spikelets narrow, the rachilla joints slender, somewhat elongate, usually not 



hidden by the florets; sheaths minutely roughened; culms solitary or in 



small tufts; shady bogs. 



Intermediate nerves of lemma distinct; uppermost ligule acute, 3 to 4 mm. 



long; western mountains below timber line 34. P. leptocoma. 



Intermediate nerves of lemma obscure; uppermost ligule truncate, 0.3 to 

 1.5 mm. long; Great Lakes region at low altitudes. 



35. P. PALUDIGENA. 



6b. Lower panicle branches often more than 2, if only 2 not capillary and 

 elongate. 

 Florets usually converted into bulblets with dark purple base; culms swollen 



and bulblike at base 36. P. bulbosa. 



Florets normal; culms not bulblike at base. 



Glumes narrow, acuminate, about as long as the first lemma; ligule very 



short 37. P. XEMORALIS. 



Glumes lanceolate, acute, shorter than the first lemma; ligules rather prom- 

 inent, those of the culm leaves 1 to 3 mm. or more long. 

 Spikelets about 6 mm. long; lemmas 4 mm. long .... 38. P. macroclada. 

 Spikelets about 4 mm. long; lemmas 2.5 to 3 mm. long. 



Culms decumbent at the purplish base; panicle 10 to 30 cm. long, large 



and open 39. P. paltjstris. 



Culms erect from a green or tawny base; panicle mostly less than 10 cm. 

 long, comparatively small and few-flowered 40. P. interior. 



4. Hotnalopoae 

 One species 41. P. chaixii. 



5. Alpinae 



Blades folded or involute, firm, rather stiff. 



Ligule very short, not noticeable when viewed from the side of sheath. 



42. P. FENDLERIANA. 



