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



Spikelets rather broad, the rachilla joints short, hidden by the 

 florets; sheaths smooth; culms in dense tufts; alpine rocky 



slopes 32. P. PAUCISPICTJLA. 



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. 



33. P. LEPTOCOMA. 



Intermediate nerves of lemma obscure; uppermost ligule truncate, 

 0.3 to 1.5 mm long; Great Lake region at low altitudes. 



34. 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 35. P. btjlbosa. 



Florets normal; culms not bulblike at base. 



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



ligule very short 36. P. nemoralis. 



Glumes lanceolate, acute, shorter than the first lemma; ligules 

 rather prominent, those of the culm leaves 1 to 3 mm or 

 more long. 

 Spikelets about 6 mm long; lemmas 4 mm long. 



37. 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 38. P. palustris. 



Culms erect from a green or tawny base; panicle mostly less 

 than 10 cm long, comparatively small and few-flowered. 



39. P. INTERIOR. 

 4- Alpinae 



Blades folded or invomte, firm, rather stiff. 



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



40. P. FENDLERIANA. 



Ligule prominent, easily seen in side view, 5 to 7 mm long. 



41. P. LONGILIGULA. 



Blades flat or, if involute, rather lax or soft. 



Panicle branches slender, spreading or drooping, the lower naked and simple 



for 3 to 4 cm or more 42. P. atjtumnalis. 



Panicle branches not long and spreading. 



Panicle broadly pyramidal, condensed, about as broad as long, the lower 

 branches spreading or reflexed. Spikelets broad, subcordate. 



43. P. ALPINA. 

 Panicle longer than broad. 



Panicle nodding, the lower branches slender, arcuate-drooping. 



44. P. STENANTHA. 



Panicle erect, the lower branches short. 



Panicle rather loose, lower branches naked below, ascending (see also 

 P. macroclada) . 



Plants glaucous, culms stiffly erect 45. P. glauca. 



Plants not glaucous; culms rather lax 46. P. laxa. 



Panicle narrow, condensed, the branches short (see also P. unilateralis) . 

 Culms rather lax, not much longer than the numerous basal leaves. 



47. P. PATTERSONI. 



Culms stiff, much longer than the basal leaves.. 48. P. rupicola. 



5. Epiles 



Panicle open, 10 to 15 cm long. Blades involute, slender 49. P. involuta. 



Panicle contracted, or if open less than 10 cm long. 



Blades scabrous, filiform 50. P. cusickii. 



Blades glabrous. 



Lemmas minutely pubescent at base 51. P. unilateralis. 



Lemmas glabrous. 



Blades of the culm 2 to 3 mm wide, flat, those of the innovations slender or 

 filiform 52. P. epilis. 



