GENERA OF GRASSES OF THE UNITED STATES. 19 
The spikelets are usually awnless, but the glumes and sterile lemma 
are awned in Echinochloa and Oplismenus, and the second glume and 
sterile lemma in Tricholaena. In Eriochloa and in some species of 
Brachiaria the fertile lemma is awn-tipped. In Chaetochloa there 
are, beneath the spikelet, one or more bristles, these representing 
sterile branchlets. In Pennisetum similar bristles form an involucral 
eluster, falling with the spikelet. In Cenchrus the bristles are 
united, forming a bur. The spikelets are of two kinds in Amphi- 
earpon, aerial and subterranean. The culms are woody and perennial 
in Lasiacis and Olyra. 
Key to the genera of Paniceae. 
LD SVPILEE VAST POET CC 08 SE en Oe AS 2 
2a. Spikelets all perfect, but those of the aerial panicle not perfect- 
ing grains; the fruitful spikelets borne on subterranean 
RSTSENTV GTN CS see eA EE a a 127. AMPHICARPON. 
2b. Spikelets unisexual, the pistillate above, the staminate below on 
the branches of the same panicle; blades broad, elliptic. 
‘ OtyRA. (See p. 252.) 
ipemsnmcelets all or one kind 22220 15 ee ee ee Ee Ee 3 
3a. Spikelets sunken in the cavities of the flattened corky rachis. 
112. STENoTAPHRUM. 
peespikelets not-sunken in the rachiseas yee see CN ea 4 
4a. Spikelets subtended or surrounded by 1 to many distinct or 
more or less connate bristles, forming an involucre______ 5 
5a. Bristles persistent, the spikelets deciduous_ 124. CHArETOcHLOA. 
5b. Bristles falling with the spikelets at maturity_________ 6 
6a. Bristles not united at base, slender, often plumose. 
125. PENNISETUM. 
6b. Bristles united into a burlike involucre, the bristles 
ELE OLSEL Ysa 1) AEC Ce a een ale es ee SLL 126. CENCHRUS. 
4b. Spikelets not subtended by bristles__._........_.____-_ iG 
7a. Glumes or sterile Jemma awned (awn short and con- 
cealed in the silky hairs of the spikelet in Tricholaena, 
awn reduced to a point in Hchinochloa colonum) —__- 8 
8a. Inflorescence paniculate ; spikelets silky_ 123. TrIcHOLAENA. 
8b. Inflorescence of unilateral simple or somewhat com- 
pound racemes along a common axis; spikelets 
SMOOLM/OLMISHIG MO tS kaye ee yy ae eae 9 
9a. Blades lanceolate, broad and thin; glumes 2- 
lobed, awned from between the lobes. 
121. OpLISMENUS. 
9b. Blades long and narrow; glumes awned from 
Cher Cp Let 2 6 Se eR RE TE Rl sd 122, ECHINOCHLOA, 
7b. Glumes and sterile Jemma awnless_2-____ 10 
10a. Fruit cartilaginous-indurate, flexible, usually dark 
colored, the lemma with more or less prominent 
white hyaline margins, these not inrolled________ 11 
11a. Spikelets covered with long silky hairs, ar- 
ranged in racemes, these panicled____ 109. Vator. 
11b. Spikelets glabrous or variously pubescent but 
HOP VIOUS - OL y a ee ee ete ee 12 
