86 Karl M. Wiegand and Arthur J. Eames 



c. Spikelets 2.5 mm. long or less; leaf blades less than 15 mm. wide. 

 d. Spikelets glabrous, elliptical; sheaths and blades glabrous. 



10. P. dichotomum 

 d. Spikelets hairy. 

 e . Sheaths, or all but the lowest one, glabrous ; ligule 1 mm. long or less ; 

 blades 7-14 mm. wide, firm, the margin narrowly white-cartilaginous ; 

 spikelets oval, 1.3-1.7 mm. long. 15. P. sphaerocarpon 



e. Sheaths hairy. 

 /. Culms and sheaths with villous or hirsute pubescence ; ligule 3-5 mm. 

 long. 

 g. Spikelets 1.3-1.9 mm. long. 



h. Axis of the panicle glabrous, or, at most, with a few appressed 

 hairs; (leaf blades glabrous above or with a few pilose hairs, 

 glabrous or pubescent beneath ; upper sheaths glabrous or pilose ; 

 spikelets mostly 1.6-2 mm. long). 11. P. Lindheimeri, 



var. septentrional e 

 h. Axis of the panicle spreading-pilose, at least on the lower inter- 

 nodes ; (upper sheaths usually pilose). 

 i. Spikelets 1.6-1.9 mm. long; leaf blades densely or loosely short- 

 pilose or glabrous above, pubescent or glabrous beneath. 



11a. P. Lindheimeri, 



var. fascictdatum 

 i. Spikelets 1.3-1.5 mm. long; leaf blades long-pilose above, with 

 hairs mostly 3-6 mm. long; whole plant conspicuously long- 

 pilose, lib. P. Lindheimeri, 



var. implicatum 



g. Spikelets (1.9) 2-2.2 mm. long; culms and sheaths copiously long- and 



somewhat matted-pilose ; leaves pubescent beneath, copiously pilose 



above, the hairs as in no. 11a; branches of the panicle possibly less 



spreading than in no. 11a, which this species resembles. 



12. P. villosissimntn 

 f. Culms and sheaths crisp-puberulent. 



g. Main leaves 3-10 mm. wide, puberulent beneath, with a few long 

 -hairs above; ligule 0.8-2 mm. long; spikelets 1.8-1.9 mm. long. 



13. P. tsugetorum 



g. Main leaves 8-15 mm. wide, glabrous on both surfaces; ligule almost 

 obsolete ; spikelets 2.2-2.5 mm. long. 14. P. umbrosum 



c. Spikelets 2.7 mm. long or more ; leaf blades 9-35 mm. wide. 

 d. Spikelets 2.7-3 mm. long. 



e. Sheaths glabrous or nearly so ; leaf blades 9-12 mm. wide. 



[P. calliphyllum] 

 e. Sheaths papillose-hispid ; leaf blades 12-30 mm. wide. 



17. P. clandestinum 

 d. Spikelets 3.2^4.5 mm. long. 



e. Leaf blades strongly ascending or erect, scarcely auricled at base; spike- 

 lets obovoid, obtuse, strongly nerved. 

 /. Panicle contracted; leaves 10-20 mm. wide. 16. P. xanthophysum 



f. Panicle open; leaves 6-12 mm. wide. [P. macrocarpon] 



c. Leaf blades more or less spreading, 15-40 mm. wide, subcordate, clasping; 

 panicle open; spikelets ellipsoidal, subacute, less strongly nerved. 

 /. Nodes strongly bearded ; plant often pubescent ; spikelets 4-4.5 mm. 



long. 18. P. Boscii 



f. Nodes glabrous or puberulent ; plant glabrous or nearly so ; spikelets 

 3.5-3.8 mm. long. 19. P. latifolium 



1. P. capillare L. Old Witch Grass. 



Sandy or gravelly cultivated fields, roadsides, and waste places, in the richer soils ; 

 common. Aug.-Sept. 



Me. to N. Dak. and Colo., southw. to Fla. and Tex., including the Coastal Plain. 



