GENERA OF GRASSES OF THE UNITED STATES. 21 



Key to the genera of Andropogoneae. 



la. Spikelets all perfect, surrounded by a copious tuft of soft hairs 2 



2a. llacliis continuous, the spikelets falling ; spikelets of the pair un- 

 equally pedicellate 3 



3a. Racemes in a narrow spikelike panicle, spikelets awn- 

 less > 128. IMPERATA. 



3b. Racemes in a broad fan-shaped panicle; spikelets awned. 



129. MlSCANTHtJS. 



2b. Rachis breaking up into joints at maturity with the spikelets at- 

 tached ; one spikelet sessile, the other pedicellate 4 



4a. Spikelets awnless 130. SACCHARUM. 



4b. Spikelets awned 131. ERIANTHTJS. 



Ib. Spikelets unlike, the sessile perfect, the pedicellate sterile (sessile 



spikelet staminate, pedicellate spikelet perfect in Trachypogon) 5 



5a. Pedicel thickened, appressed to the thickened rachis joint (at 

 least parallel to it) or adnate to it; spikelets awnless, ap- 

 pressed to the joint G 



6a. Rachis joint and pedicel adnate, forming a short flat joint, 

 this sunken in the open side of the globose first glume of 

 the sessile spikelet; sterile spikelet conspicuous 140. RYTILIX. 

 6b. Rachis joint and pedicel distinct, the sessile spikelet ap- 

 pressed to them, its first glume lanceolate 7 



7a. Racemes subcylindric ; rachis joints and pedicels glabrous, 

 much thicker at the summit, the spikelets sunken in the 



hollow below ; sterile spikelet rudimentary 130. MANISURIS. 



7b. Racemes flat ; rachis joints and pedicels woolly, not much 

 thicker at the summit; sterile spikelet staminate or neu- 

 ter 138. ELYONURUS. 



5b. Pedicel not thickened (if slightly so the spikelets awned), neither 

 appressed nor adnate to the rachis joint, this usually slender ; 



spikelets usually awned ^ 8 



8a. Fertile spikelet with a hairy-pointed callus, formed of the 



attached supporting rachis joint or pedicel ; awns strong 9 



9a. Racemes reduced to a single joint, long-peduncled in a 



simple open panicle 135. RHAPHIS. 



9b. Racemes of several to many joints, single 10 



lOa. Primary spikelet subsessile, sterile, persistent on 

 the continuous axis after the fall of the fertile pedi- 

 cellate spikelet, the pedicel forming the callus. 



137. TRACHYPOGON. 



lOb. Primary spikelet sessile, fertile; pedicellate spike- 

 let sterile ; lower few to several pairs of spikelets all 



staminate or neuter 136. HETEROPOGON. 



8b. Fertile spikelet without a callus, the rachis disarticulating 



immediately below the spikelet ; awns slender 11 



lla. Racemes of several to many joints, solitary, digitate, 



or aggregate 132. ANDROPOGON. 



lib. Racemes reduced to one or few joints, these mostly 



peduncled in a subsimple or compound panicle 12 



12a. Pedicellate spikelets staminate 133. HOLCUS. 



12b. Pedicellate spikelets wanting, the pedicel only 

 present 134. SORGHASTRUM. 



