136 GRAMINEAE. VOL. I. 



Culms erect, the branches fasciculate near the middle. 



35. P. dichotomum. 

 Culms at length long and trailing, branches fasciculate at all the nodes. 



36. P. lucidum. 

 Spikelets 1%" long. 37- P- yadkinense. 



Spikelets pubescent. 



Sheaths glabrous, the margins ciliate, or the basal ones sometimes pubescent. 

 Blades velvety. 39- P- annulum. 



Blades not velvety. 



Ligule Yz" long or less. 



Spikelets less than i" long. 



Culms slender, the leaf-blades i' long or less ; spikelets elliptic. 



33. P. ensifolium. 



Culms stouter, the leaf-blades larger ; spikelets nearly globose. 

 Panicle longer than broad ; upper leaf-blades not smaller than 



the lower. 32. P. polyanthes. 



Panicle nearly as long as broad ; upper blades smaller than the 



lower ones.. 



Blades less than 4" wide, glabrous. 34. P. tenue. 

 Blades exceeding 4" wide, ciliate on the margins toward 



the base. 31. P. sphacrocarpon. 



Spikelets over i" long. 



Culms puberulent. 71. P. Ashei. 



Culms glabrous. 



Leaf-blades cordate, usually over 5" wide. 72. P. commutatum. 

 Leaf-blades not cordate at the base, usually less than 5" wide. 

 Blades erect, ciliate toward the base ; fruiting scale not exceed- 

 ing the others. 40. P. boreale. 

 Blades spreading, glabrous ; fruiting scale exceeding the other 

 scales. 41. P. mattamuskeetense. 

 Ligule i"-2 l /2 rr long. 



Spikelets over i" long. 48. P. scoparioides. 



Spikelets less than i" long. 



Panicle much longer than broad. 



Spikelets less than -K" long, almost globose when mature, 



sparsely pubescent with short hairs. 43. P. paucipiluni. 

 Spikelets over tya," long, elliptic, densely pubescent with long hairs. 



44. P. spretum. 



Panicle as long as broad. 45. P. Lindheimeri. 



Sheaths pubescent. 



Sheaths merely puberulent. 



Spikelets elliptic, over i" long. 71. P. Ashei. 



Spikelets obovoid, i" long. 60. P. Nashianum. 



Sheaths pubescent with longer hairs. 

 Plants velvety. 



Spikelets over i" long. 



Culms stout, a broad bare ring below each node; spikelets i"-iJ4" 



long; primary panicles exceeding 3' long. 67. P. scoparium. 

 Culms slender; no conspicuous bare ring; spikelets iY^"-iy 2 " long; 



panicle less than 3' long. 68. P. malacophyllum. 



Spikelets less than i" long. 



Hairs on the sheaths long and shaggy; ligule over i" long. 



55. P. lanuginosum. 

 Hairs on the sheaths short and inconspicuous ; ligule less than Yz" 



long. 39. P. annulum, 



Plants not velvety. 



Spikelets ovate, pointed ; blades and panicles usually 5' long or more. 



69. P. scabriusculum. 



Spikelets not as above ; blades and panicles shorter. 

 Spikelets less than i" long. 

 Pubescence spreading. 



Blades glabrous above or nearly so. 54. P. tennesseensc. 

 Blades pubescent on the upper surface. 



Upper surface of blades with short appressed hairs. 



47. P. huachucae. 



Upper surface with long erect hairs 1 J/" long or more. 

 Culms forming branches when primary panicles are 



mature; spikelets Y^" long. 

 Panicle i'-i%' long, its axis minutely pubescent. 



52. P. meridionale. 

 Panicle 2'- 3' long ; axis hirsute. 51. P. implicatum. 



Culms forming branches before maturity of primary 



panicles; spikelets i" long. 50. P. praecocius. 

 Pubescence not spreading. 



Ligule obsolete ; culms villous-puberulent. at least below. 



Culms with 2 or 3 primary leaves, the blades 1^2" wide 

 or less, up to 3'-4' long, branches crowded at the base. 



53. P. Owenae. 



Culms with 4-6 primary leaves, the blades 2"-4" wide, 

 usually less than 3' long, branches at all the nodes. 

 Culms erect, rigid ; plants grey green. 



58. P. columbianum. 



Culms weak, fasciculately decumbent and forming 

 mats ; plant blue-green. 59. P. tsugetorum. 



