34 POACEAE 



XI. Aridae. 

 Internerves of the lemma pubescent, at least below; stem stout; inflorescence dense; 

 ligules acute. 

 Intermediate ner\'^s of the lemma strong; plant tall; glumes 5 mm. long. 



33. P. pratensiformis. 

 Intermediate nerves of the lemma weak; glumes 3-4 mm. long. 



Keel and the marginal nerves of the lemma villous; empty glumes equalling the 



lemma. 34. P. arida. 



Keel and marginal nerves of the lemma short-hairy, with appressed hairs; empty 

 glumes shorter than the lemma. 35. P. Sheldoni. 



Internerves of the lemma glabrous; stem slender; inflorescence open; ligule obtuse. 



36. P. glaucifoUa. 



XII. RUPICOL.\E. 



Midnerve and lateral nerves of the lemma pubescent; plant strict, 1-5 dm. high. 



Cobweb at the base of the flowers scant; stem slender and leafy, iisually 3-5 dm. 



high. 23. P. crocala. 



Cobweb none; stem 1-2 (seldom 3) dm. liigh, leafy mostly at the base. 



Flowering glumes 3 mm. long or less, firm, obtuse. 37. P. rupicola. 



Floweruig glumes about 4 mm. long, acute, thin. 38. P. Pattersoni. 



Nerves of the lemma glabroiLs; plant seldom over 5 cm. high. 39. P. Letlermani. 



XIII. MULTNOMAE. 



One species. 40. P. Mullno>7iae. 



XIV. Epiles. 

 Plant green; lemma purple or dark green, abruptly acute; ligules acute. 



Blades of the stem-leaves about 3 mm. wide, flat; lemma more than 5 mm. long. 



dark purple. 41 . P. paddensis. 



Blades of the stem-leaves 1-2 mm. wide; lemma 4-5 mm. long. 



Lemma purple, minutely scabrous, nearly smooth. 42. P. Cusickii. 



Lemma green, only tinged with purple, hispidulous-scabrous. 



43. P. epilis. 

 Plant pale; lemma very pale, long-attenuate or subcuspidate; leaves all fiUform. 



Ligules lanceolate, acuminate. 



Panicle thick; branches with several 5-7-flowered spikelets; leaves very scabrous. 



44. P. scaberrima. 

 Panicle narrow, slender; branches very short, with 1-2, only 2-4-flowered spike- 

 lets. 45. P. nemalophylln. 



Ligules oblong, 1 mm. long, trimcate; panicle dense and spike-Uke. 



46. P. suharistala. 



XV. GRACII.LIMAE. 



Lemma Imear-lanceolate, 5-6 mm. long. 47. P. idahoensis. 



Lemma ovate, 4-5 mm. long. 



Plant 1-3 dm. high; panicle with ascending branches and many spikelets. 



48. P. gracillima. 

 Plant 0.5-1.5 dm. high; panicle with divaricate Iiranches and few spikelets. 



49. P. Vaseyochloa. 



XVI. FENDLEniAXAE. 



Ligules 5-7 mm. long, acute or acuminate. 50. P. longiligula. 



Ligules short, roimded or truncate, or those of the innovations obsolete. 

 Leaf-blades erect; spikelets 3-5- (rarely 6-7-) flowered. 



Lemma oblong; leaf-blades very slender, scabrous. 51. P. scabriuscula. 



Lemma ovate; leaf-blades more rigid. 



Panicle very narrow, its branches erect and spikelet-bearing to the base; 

 lemma 4 mm. long. 52. P. longipeduncitlata. 



Panicle more open, its branches ascending, usually naked at the base. 



Plant low; panicle short; lemma 3.5-4 mm. long. 53. P. hrevipaniculata. 

 Plant tall; panicle elongated; lemma 5 mm. long. 54. P. Fendleriana. 

 Leaf-blades spreading; spikelets 7-9- (rarely 5-6-) flowered. 55. P. Eatoni. 



XVII. BUCKLEYANAE. 



Ligules lanceolate, acuminate or attenuate. 



Empty glumes strongly nerved, elongate-lanceolate, almost equalling the very scab- 

 rous or strigose lemma. 

 Leaves 4-6 mm. wide, flat. 56. P. Canbyi. 



Leaves 1-3 mm. wide, conduplicate or involute. 



Lemma strongly scabrous; leaves stiff; plant stout. 57. P. nevadensis. 

 Lemma strigose, at least below; leaves flliform, flaccid; plant slender. 



58. P. Helleri. 

 Empty glumes not strongly nerved, ovate-lanceolate, usually much shorter than the 

 lemma. 

 Plant yellowish green; spikelets yellowish or straw-colored. 



Lemma merely scabrous. 59. P. laevigata. 



Lemma more or less strigose on the lower portion. 60. P. lucida. 

 Plant dark green; spikelets dark green or purplish. 



Leaf-blades almost 2 mm. wide, flat or conduplicate; lemma more than 4 mm. 



long. 61. P. Bucklcyana. 



Leaf-blades le^s than 1 mm. wide, fihform, involute; lemma less than 4 mm. long. 



62. P. Sandbergii. 



