34 POACEAE 



XI. Aridae. 

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

 ligules acute. „ , 



Intermediate nerves 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 equallmg the 



lemma. . ,^34. P. arida. . 



Keel and marginal nerves of the lemma short-hau'y, with appressed najrs; empty 

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



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



36. P. glaucifolia. 



XII. EUPICOLAE. 

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



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



higli. 23. P. crocata. 



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



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



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



Nerves of the lemma glabrous; plant seldom over 5 cm. high. 39. P. I.eUermani. 



XIII. MULTNOMAE. 



One species. 40. P. MuUnomae. 



XIV. EPIIXS. 

 Plant green; lemma piirple 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 filiform. 



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. nematophylla. 



Ligules oblong, 1 mm. long, truncate; panicle dense and spike-like. 



46. P. subaristata. 



XV. GRACII.UMAB. 



Lemma linear-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 branches and few spikelets. 



49. P. Vaseyochloa. 



XVI. FENDI.Er.IAXAE. 



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



Ligules short, rounded 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. longipedunculata. 



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. Ealoni. 



XVII. Bdckletanae. 

 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 filiform, 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 strigo.se 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. BuckUyana. 



Leaf-blades le<is than 1 mm. wide, fiUform, involute ; lemma less than 4 mm. long. 



62. P. Sandbergii. 



