76 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



A Ligule manifest, 2-5 mm. long (1-1.5 mm. long in P. tmgetorum). 

 Sheaths glabrous or the lowest sometimes pubescent. 

 Panicle narrow, one-fourth to one-third as wide as long 27 P spretum 



Panicle open, nearly aa wide as long 28 . P. lindheimeri ; 



Sheaths pubescent. 

 Spikelets 2.2-2.4 mm. long. 

 Pubescence on culms horizontally spreading; autumnal phase freely branching. 

 ^ , 33. P. villosissimum. 



t ubeseence on culms appressed or ascending; autumnal phase rather sparingly 



branching 34 p ^ ^^ 



Spikelets less than 2 mm. long. 

 Vernal blades glabrous or nearly so on the upper surface. 



Ligule 1-1.5 mm. long; culm crisp-puberulent 36. P. tsugetorum. 



Ligule 4-5 mm. long; culm papillose-pilose or becoming glabrous. 



32. P. tennesseense. 

 Vernal blades pubescent on the upper surface. 

 Spikelets 1.3-1.5 mm. Long; vernal blades long-pilose on the upper surface. 

 Autumnal phase widely decumbent-spreading, forming a mat, the vernal 

 culma soon genicu late-spreading; plants grayish olivaceous. 



30. P. albemarlense. 

 Autumnal phase erect, not forming a mat; plants yellowish green. 



a ., , . , a , „ , 29. P. meridionale. 

 bpikelets 1.6-1.8 mm. long; vernal blades appressed-pubescent 

 Blades stiff, erect 31. P. huachucae. 



« a t- i , f ' s P readin S 31a. P. huachucae silvicola. 



AA. Ligule obsolete or less than 1 mm. long. 



Nodes bearded. 



Blades velvety on „ . 



T,, , , , J 20. P. annulum. 



tf lades glabrous, or only the lower pubescent. 



Sheaths and upper nodes glabrous 22. P. clutei 



Sheaths, at least the lower ones, and all the nodes pubescent. 



w , .. . , 21. P. mattamuskeetense. 



Nodes not bearded. 



Plants densely gray-velvety throughout, a viscid glabrous ring below the nodes. 



™ . , 44. P. scoparium. 



riants not gray -velvety. 



Sheaths, or some of them, pilose or hispid . 



Pubescence papillose-hispid 48. P. clandestinum. 



Pubescence ascending-pilose. 



Spikelets 2 mm. long 36. P. addisonii. 



« X i f 3 mm - bng 37a ' P " eolumbianum thinium. 



telieaths glabrous or only puberulent. 



Spikelets spheric, not over 1.8 mm. long. Blades with a thin white carti- 

 laginous margin. 



Culms spreading; panicle as broad as long 38 . P. sphaerocarpon. 



^ Culms erect; panicle two-thirds as broad as long 39. p. polvanthes 



Spikelets not spheric. 

 Spikelets 2.5 mm. long. 



Upper blades elongate, narrowed toward the base 18. P. bicknellii. 



Upper blades not elongate, cordate at base. 

 Culms crisp-puberulent; blades usually less than 1 cm. wide. 



n . , , 46. P. ashei. 



Culma glabrous; blades usually 1.5 era. wide or more. 



47. P. commutatum. 



