76 CONTRIBUTIONS FROM THE NATION AX. HERBARIUM. 



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

 Sheaths glabrous or the lowest sometimes pubescent. 



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



Panicle open, nearly as 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. 

 Pubescence on culms appressed or ascending; autumnal phase rather sparingly 



branching 34. P. pseudopubescens. 



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 

 culms soon geniculate-spreading; plants grayish olivaceous. 



30. P. albemarlense. 

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



29. P. meridionale. 

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



Blades stiff, erect 31. P. huachucae. 



Blades lax, spreading 31a. P. huachucae siMcola. 



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

 Nodes bearded. 



Blades velvety 20. P. annulum. 



Blades 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. 



21. P. mattamuskeetense. 

 Nodes not be arded . • 



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



44. P. scoparium. 

 Plants not gray -velvety. 

 Sheaths, or some of them, pilose or hispid. 



Pubescence papillose-hispid 48. P. clandestinum. 



Pubescence ascending-pilose. 



Spikelets 2 mm. long ; 35. P. addisonii. 



Spikelets 1.3 mm. long 37a. P. columbianum thinium. 



Sheaths 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. sphaerooai-pon. 



Culms erect; panicle two-thirds as broad as long 39. P. polyanthes. 



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. 



46. P. ashei. 

 Culms glabrous; blades usually 1.5 cm. wide or more. 



47. P. commutatum. 



