148 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Spikelets abruptly pointed; blades cordate; 
Mexican . ..------0-- eee eee eee eee ee eees 179. P. viscidellum. 
Spikelets not pointed at maturity; blades not 
cordate. 
Ligule 1 mm. long; sheaths sparsely pilose; 
spikelets 1.4 mm. long.........-------- 159. 
Ligule usually more than 1 mm. long. 
Ligule 1 to 1.5 mm. long; culms and 
sheaths appressed-pubescent; spike- 
lets 1.5 to 1.9 mm. long. 
Spikelets 1.8 to 1.9 mm. long; plants 
bluish green.......------------+-- 146. 
Spikelets 1.5 mm. long, nearly globular; 
plants olivaceous.......------+---+-- 148. 
Ligule 2 to 5 mm. long. 
Spikelets | to 1.3 mm. long; culms and 
sheaths softly appressed-pubescent. 
Spikelets 1.2 to 1.3 mm. long......... 118. 
Spikelets not over | mm, long.......- 120. 
Spikelets mostly more than 1.5 mm. 
. curtifolium. 
. tsugetorum. 
. oricola. 
. leucothriz. 
. wrightianum. 
long, if less, pubescence spreading. See LANUGINOSA 
Ligule obsolete or less than 1 mm. long. 
Nodes bearded (P. scoparium may appear to be 
bearded). 
Spikelets nearly 3 mm. long; plants velvety- 
villous throughout..........----.-...-+-- 169. 
Spikelets rarely as much as 2.5 mm. long; 
plants not pubescent throughout. 
Spikelets 1.5 to 1.6 mm. long...---.---...-- 102. 
Spikelets 2 mm. or more long. 
Blades all velvety; autumnal form spar- 
ingly branched............---------- 105. 
Blades glabrous, or only the lower pubes- 
cent or velvety. 
Spikelets 2 mm. long; autumnal form 
profusely branching. 
Fruits slightly exposed at maturity; 
upper sheaths viscid-spotted...... 103. 
Fruits covered at maturity; sheaths 
not viscid-spotted; Mexican. --. .104. 
Spikelets 2.2 mm. or more long; autum- 
nal form less profusely branching. 
Sheaths and upper nodes glabrous. . . . 107. 
Lower sheaths and all nodes pubes- 
cent ...22222e eee eee ee eee ee 106. 
Nodes not bearded. 
Plants densely gray-velvety throughout, a 
viscid, glabrous ring below the nodes..... 178. 
Plants not gray-velvety. 
Sheaths or some of them pilose or hispid. 
Pubescence papillose-hispid. 
Spikelets ovate, pointed, 2.3 to 2.6 mm. 
~ 
~ 
ww 
~ 
~~ 
(p. 208). 
. malacophyllum. 
. microcarpon. 
. annulum. 
. nitidum. 
. multirameum. 
. cluter. 
mattamuskee- 
tense. 
. scoparium. 
. scabriusculum. 
