258 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Ensifolia.—Plants low and slender, usually glabrous and less than 50 cm. high; 
sheaths glabrous or puberulent (sparsely pilose in P. curtifolium); ligules 
nearly obsolete (about 1 mm. long in P. curtifolium); panicles small, rarely 
more than 5 cm, long; spikelets glabrous or pubescent, 1 to 1.7 mm. long, 
5 to 7-nerved. Autumnal form sparingly to freely branching, or in P, vernale 
a distinct autumnal form wanting. , 
Ligules about 1 mm. long; sheaths or some of them sparsely 
spreading-pilose.............--------------2-2-2-2---- 159. P. curtifolium. 
Ligules obsolete or nearly so; pubescence if present not 
spreading. 
Blades prominently white-margined, firm; spikelets 
densely puberulent. 
Blades puberulent beneath, often above; sheaths 
and sometimes lower internodes ascending 
pubescent .......--.---------2---------2-+------ 152. P. tenue. 
Blades glabrous; sheaths glabrous or minutely ciliate 
only. 
Uppermost culm blades much reduced; culms 
branching from lower nodes only, the 
branches repeatedly branching.........-.. 153. P. albomarginatum. 
Uppermost culm blades about as long as the 
others; culms bearing short branches from 
the upper and middle nodes ........-..-- 154. P. trifolium. 
Blades not white-margined or very obscurely so (or if white 
margin is evident spikelets only 1.1 mm. long); 
spikelets glabrous or puberulent. 
Culms branching only at base; plants soft, light green.158. P. vernale. 
Culms branching at the nodes; plants firm or at least 
not soft. 
Spikelets glabrous. 
Spikelets 1.1 to 1.2 mm. long; blades rarely 
as much as 5 em, long..........----- 160. P. chamaelonche. 
Spikelets 1.2 to 1.5 mm. long. 
Blades elongated, at least some of them 
8 to 10 cm. long............-....-161. P. glabrifolium. 
Blades not over 3 cm. long...........-- 157. P. ensifolium. 
Spikelets puberulent. 
Spikelets 1.1 mm. long; winter blades bluish 
green, not glossy....-....-.--------- 156. P. concinnius. 
Spikelets 1.3 to 1.5 mm. long. 
Blades involute, faleate, with long stiff 
hairs on margin near base; plants 
stiff and wiry....--......-------- 162, P. breve. 
Blades not involute, or at tip only, not 
falcate. 
Plants bright green; winter blades 
conspicuous, glossy green... . . 15 
Plants olive; winter blades not con- 
spicuous nor glossy........-- 157. P. ensifolium. 
ey 
5. P. flavovirens. 
