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.290), 
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. viscidellum..........++++22+------ 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. asher); 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)...ENsSIFOLIA (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.......---------eee-ee NuDICAULIA (p. 179). 
Lower internodes not shortened; 
vernal culms about evenly 
leafy throughout, spikelets el- 
liptic or obovate, not over 2.5 
mm. long........-...------------Dicnotoma (p. 179). 
