MANUAL OF THE GRASSES OF THE UNITED STATES 617 



Spikelets not more than 1.7 mm long. 



Blades white-margined; spikelets 1.6 to 1.7 mm long, 



elliptic 73. P. tenue. 



Blades not white-margined; spikelets 1.3 to 1.4 mm 

 long, nearly globular. 



" 68. P. COLUMBIANUM var. thinium. 

 16b. Sheaths glabrous or puberulent only. 



17a. Spikelets spherical, not more than 1.8 mm long. 

 Blades cordate, ciliate at base. 



See 10. Sphaerocarpa. 



17b. Spikelets not spherical. 



18a. Culms soon prostrate, vinelike; branches divaricate. 

 Plants bright green; culms lax; spikelets not more than 



2.1 mm long 36. P. lucidum. 



Plants gravish green; culms stiff; spikelets 2.5 mm long. 



37. P. SPHAGNICOLA. 



18b. Culms not vinelike; branches not divaricate. 



19a. Spikelets asymmetrically pyriform, strongly 



nerved. Culms wiry See 12. Lancearia. 



19b. Spikelets not pyriform. 



20a. Blades elongate, especially the upper, about 



20 times as long as wide. Spikelets about 2.5 



mm long, on long pedicels. 22. P. bicknellii. 



,_ J . ± . , 20b. Blades not elongate. (See continuation.) 

 (Continuation.) 



21a. Spikelets 2 mm long or more. 



Spikelets 2.5 to 3 mm long; blades cordate, usually 1 cm or more wide. 



Plants glaucous; basal blades conspicuously ciliate 105. P. mutabile. 



Plants not glaucous; basal blades ciliate at base only. 



Culms crisp-puber; dent; blades rarely more than 1 cm wide; spikelets about 



2.5 mm long 103. P. ashei. 



Culms glabrous or obscurelv puberulent; blades usually 1.5 cm wide or 



more; spikelets 2.7 to 3' mm long 104. P. commutatum 



Spikelets not more than 2.3 mm long; blades not cordate, usually less than 1 

 cm wide. 

 Blades conspicuously ciliate, soft, lax, crowded at the base. 



11. P. CILIATTJM. 



Blades not ciliate or at base only, not crowded at the base. 



Blades not more than 6 mm wide; plants not branching or rarely branching 



from near the base 8. P. werneri. 



Blades 7 mm wide or more; plants branching from middle and upper nodes. 

 Primarv blades spreading; panicle purplish; fruit exposed at summit. 



29. P. CLUTEI. 

 Primary blades erect; panicle green; fruit covered.. 30. P. boreale. 

 21b. Spikelets not more than 1.7 mm long. 



Culms crisp-puberulent. Spikelets turgid 68. P. columbianum. 



Culms glabrous. 



Blades white-margined, firm. 



Blades puberulent beneath, often above 73. F. tenue. 



Blades glabrous. 



Uppermost blades much reduced; culms branching from lower nodes 

 only, the branches repeatedly branching. 



74. P. albomarginatum. 

 Uppermost blades about as long as the others; culms bearing short 



branches from middle and upper nodes 75. P. trifolium. 



Blades not white-margined or very obscurely so (or if white margin is 

 evident, spikelets only 1.1 mm long). 

 Culms branching only at base. Plants soft, light green. 79. P. vernale. 

 Culms branching at the nodes. 



Spikelets 1.1 mm long. Winter blades bluish green, not glossy. 



77. P. CONCINNIUS. 



Spikelets 1.3 to 1.5 mm long. 



Blades involute, falcate, with long stiff hairs on margin near base. 



Plants stiff and wiry 83. P. breve. 



Blades not involute or at tip only, not falcate. 



Plants bright green; winter blades conspicuous, glossy green. 



76. P. FLAVOVIRENS. 



Plants olive; winter blades not conspicuous nor glossy. 



78. P. ENSIFOLIUM. 



