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



Culms not vinelike; branches not divaricate. 

 Spikelets 2.3 to 2.6 mm long. 



Blades, or some of them, at least 8 mm wide; fruit papillose- 

 roughened 87. P. WEBBERIANUM. 



Blades not more than 6 mm wide; fruit smooth and shining. 



88. P. PATENTIFOLIUM. 



Spikelets 2 mm long. 



Culms wiry, crisp-puberulent; blades ciliate at base. 



85. P. LANCEARITJM. 



Culms glabrous; blades not ciliate. 



Blades erect, firm; spikelets turgid, strongly nerved. Plants 



grayish olive 34. P. roanokense. 



Blades spreading; spikelets not turgid. 



Nodes glabrous; autumnal phase erect, branched like a 



little tree 31. P. dichotomum. 



Nodes, at least the lowest, usually bearded; autumnal 



phase topheavy-reclining 32. P. barbtjlatum. 



lb. Spikelets pubescent. 



6a. Spikelets 3 mm or more long. 



7a. Blades elongate, those of the midculm at least 15 times as long as wide. 

 Secondary panicles from basal sheaths only. 



Spikelets pointed, about 3.5 mm long 5. P. depauperatum. 



Spikelets blunt, 3 mm long or less 6. P. perlongum. 



Secondary panicles from upper branches. 



Spikelets attenuate at base, pustulose-pubescent; lowermost sheaths 



softly villous 18. P. fusiforme. 



Spikelets not attenuate at base, not pustulose; lowermost sheaths 

 glabrous or hispid. 

 Upper leaves approximate; sheaths glabrous. 



107. P. equilaterale. 

 Upper leaves distant; at least the lower sheaths hispid. 



100. P. ACULEATTJM. 



7b. Blades not elongate, usually less than 10 times as long as wide. 

 8a. Blades velvety-pubescent beneath. 



Spikelets 3 mm long. Plants velvety-villous throughout. 



90. P. MALACOPHTLLUM. 



Spikelets 4 mm long or more. 



Sheaths ascending-hirsute, ligule 3 to 4 mm long. 



94. P. RAVENELII. 



Sheaths downy-pubescent; ligule obsolete. 



110. P. boscii var. molle. 

 8b. Blades not velvety-pubescent beneath. 



9a. Sheaths glabrous or minutely puberulent only. 



Nodes bearded; spikelets 4 mm long or more 110. P. boscii. 



Nodes not bearded; spikelets not more than 3.8 mm long. 

 Spikelets 3.5 to 3.8 mm long. Blades 2 cm wide or more. 



109. P. LATIFOLIUM. 



Spikelets scarcely more than 3 mm long. 



Spikelets turgid, blunt; blades mostly less than 1 cm wide. 



91. P. HELLERI. 



Spikelets not turgid; blades more than 1 cm wide. 



Panicle narrow, the branches ascending. Spikelets on long 

 stiff pedicels 23. P. calliphyllum. 



Panicle as broad as long, the branches spreading. 

 Plants glaucous; basal blades conspicuously ciliate. 



105. P. MTJTABILE. 



Plants not glaucous; basal blades not ciliate, or at the base 

 only. 

 Culms erect, or autumnal phase leaning; blades sym- 

 metrical, broadly cordate 104. P. commutatum. 



Culms decumbent; blades usually unsymmetrical and 

 falcate, narrowed to the scarcely cordate base. 



106. P. joorii. 



