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



Spikelets obtuse; culms not weak and lax. 



Culms leafy below, branching from base and lower nodes; Maine 



to Minnesota 52. P. subvillostjm. 



Culms evenly leafy, branching from upper nodes; Pacific slope. 



54. P. PACIFICUM. 

 Upper surface of blades appressed-pubescent or pilose toward the base 

 only; spikelets 1.6 to 1.8 mm long; autumnal phase not decum- 

 bent-spreading 46. P. HUACHUCAE. 



lb. Spikelets 2.2 mm long or more. 

 Spikelets 2.2 to 2.4 mm long. 



Pubescence on culms horizontally spreading; autumnal phase freely branch- 

 ing 57. P. VILLOSISSIMUM. 



Pubescence on culms appressed or ascending; autumnal phase rather spar- 

 ingly branching. 

 Upper internodes shortened, the leaves approximate, the blades often equal- 

 ing the panicle; pubescence sparse and stiff-- 60. P. scoparioides. 

 Upper internodes not shortened, the copious pubescence silky. 



58. P. PSEUDOPUBESCENS. 



Spikelets 2.7 to 2.9 mm long. 



Culms stiff; blades conspicuously ciliate; southern Atlantic coast. 



59. P. OVALE. 



Culms weak; blades not ciliate; Pacific coast 61. P. shastense. 



9. Columbiana 



la. Spikelets 2 to 3.2 mm long, mostly elliptic. 



Winter blades 5 to 10 cm long. Spikelets 2 mm long; plants blue-green. 



66. P. WILMINGTONENSE. 



Winter blades 1 to 3 cm long. 



• Spikelets 3.2 mm long; first glume conspicuously distant- 62. P. malacon. 

 Spikelets not more than 2.9 mm long; first glume not distant. 

 Spikelets 2.8 to 2.9 mm long; vernal blades 8 to 15 cm long. 



63. P. DEAMII. 



Spikelets not more than 2.4 mm long; vernal blades not more than 8 cm 

 long. 

 Spikelets about 2.4 mm (2.2 to 2.4 mm) long; panicle open, the branches 



stiffly spreading 64. P. commonsianum. 



Spikelets 2 to 2.1 mm long; panicle rather dense, the branches ascending. 



65. P. ADDISONII. 

 lb. Spikelets not more than 1.9 mm long, obovate, turgid. 



Culms crisp-puberulent or appressed-pubescent with crimped hairs; plants 

 bluish or grayish green; panicle about 3 to 7 cm long. 



Spikelets 1.8 to" 1.9 mm long 67. P. tsugetorum. 



Spikelets 1.5 to 1.6 mm long 68. P. columbianum. 



Culms appressed or ascending-pilose; plants olivaceous; panicle rarely more 



than 3 cm long. Spikelets not more than 1.5 mm long, rounded and turgid. 



Spikelets 1.5 mm long; culms rather stout; autumnal phase branching from 



all the nodes 69. P. oricola. 



Spikelets 1.3 to 1.4 mm long; culms very slender; autumnal phase with 

 branches mostly aggregate toward the summit. 



68. P. COLUMBIANUM Var. THINIUM. 



10. Sphaerocarpa 

 Culms spreading; blades obscurely nerved; panicle nearly as broad as long. 



70. P. SPHAEROCARPON. 



Culms erect or ascending; blades rather strongly nerved; panicle never more than 

 two-thirds as broad as long, usually less. 

 Spikelets 1.5 to 1.6 mm long; blades lanceolate, the upper not reduced. 



71. P. POLYANTHES. 



Spikelets 1 to 1.2 mm long; blades tapering from base to apex, the upper much 

 smaller than the lower 72. P. erectifolium. 



