HITCHCOCK AND CHASE NORTH AMERICAN PANICUM. 143 



Spikelets not turgid, blunt, nor strongly nerved (see, 

 however, P. roanokense and P. caerulescens.) 

 Ligule of conspicuous hairs, usually 3 to 5 mm. 

 long. 

 Sheaths glabrous or only the lowermost some- 

 what pubescent Spreta (p. 200). 



Sheaths strongly pubescent Lanuginosa (p. 208). 



Ligule obsolete or nearly so (manifest in P. vis- 

 cidellum, P. oricola, P. tsugetorum and P. cur- 

 tifolium.) 

 Spikelets spherical at maturity; blades glabrous, 



firm, cordate; plants sparingly branching. . . Sphaerocarpa (p. 250). 

 Spikelets usually obovate or elliptic. 



Blades of mid-culm elongated, less than 1.5 cm. 

 wide; culms usually tall; spikelets pointed, 

 abruptly so in the velvety P. scoparium 



and P. vistidellum Scoparia (p. 294). 



Blades of mid-culm not elongated (somewhat so 

 in P. equilaterale) . 

 Blades cordate, 1 to 3 cm. wide (5 to 12 mm. 

 in P. ashei) ; spikelets pubescent. 

 Spikelets 2.5 to 3 mm. long; sheaths 



glabrous or minutely puberulent Commutata (p. 300). 



Spikelets 3 to 5 mm. long (sometimes but 

 2.7 mm. long in the hispid-sheathed 



P. clandestinum Latifolia p. (312). 



Blades not cordate, less than 1 cm. wide. 

 Sheaths crisp or appressed- pubescent; 



blades firm; spikelets pubescent Columbiana (p. 240). 



Sheaths glabrous (sparsely pilose in P. 

 curtifolium and the lower, velvety 

 in P. mattamuskeetense) . 

 Vernal culms delicate (sometimes scarcely 

 so in P. albomarginatum and P. 

 tenue); spikelets 1.5 mm. or less 

 long (1.6 to 1.7 mm. in P. tenue).. .Ensifolia (p. 258). 

 Vernal culms slender but not delicate, 

 rarely less than 40 cm. high; spike- 

 lets 2 to 2.9 mm. long (1.5 mm. in 

 P. microcarpon and P. caerulescens). 

 Lower internodes shortened, upper 

 elongated, producing a nearly 

 'naked culm, leafy at base; spike- 

 lets narrowly ovate, 2.7 to 2.9 



mm. long Nudicaulia (p. 179). 



Lower internodes not shortened; 

 vernal culms about evenly 

 leafy throughout, spikelets el- 

 liptic or obovate, not over 2.5 

 mm. long Dichotoma (p. 179). 



