MANUAL OF THE GRASSES OF THE UNITED STATES 25 



Spikelets in slender racemes more or less digitate at the summit of the culms. 



129. Digitaria. 

 Spikelets in panicles. 



Fruiting lemma boat-shaped; panicles narrow 127. Anthaenantia. 



Fruiting lemma convex; panicles diffuse 130. Leptoloma. 



2b. Fruit chartaceous-indurate, rigid. 



Spikelets placed with the back of the fruit turned away from the rachis of the 

 racemes, usually solitary (not in pairs). 

 First glume and the rachilla joint forming a swollen ringlike callus below the 



spikelet 132. Eriochloa. 



First glume present or wanting, not forming a ringlike callus below the spike- 

 let. 

 First glume present (next to the axis); racemes racemose along the main 



axis 133. Brachiaria. 



First glume wanting; racemes digitate or subdigitate 134. Axonopus. 



Spikelets placed with the back of the fruit turned toward the rachis (first glume, 

 when present, away from the rachis) of the spikelike racemes or pedicellate 

 in panicles. 



Fruit long-acuminate; both glumes wanting 135. Reimarochloa. 



Fruit not long-acuminate; at least one glume present. 



First glume typically wanting ; spikelets plano-convex, subsessile in spikelike 



racemes „ 136. Paspalum. 



First glume present; spikelets usually in panicles. 

 Second glume inflated-saccate, this and the sterile lemma much exceeding 



the stipitate fruit 139. Sacciolepis. 



Second glume not inflated-saccate. 



Culms woody, bamboolike; fruit with a tuft of down at the apex. 



138. Lasiacis. 

 Culms herbaceous; no tuft of down at the apex of the fruit. 



137. Panicum. 



TRIBE 13. ANDROPOGONEAE 



Spikelets in pairs along a rachis, the usual arrangement being one of the 

 pair sessile and fertile, the other pedicellate and staminate or neuter, rarely 

 wanting, only the pedicel present; fertile spikelet consisting of 1 perfect 

 terminal floret and, below this, a staminate or neuter floret, the lemmas thin 

 or hyaline, and 2 awnless glumes, 1 or usually both firm or indurate. 



A large tribe, confined mostly to warm regions. The rachis is usually jointed, 

 disarticulating at maturity, with the spikelets attached to the joints. In a few 

 genera it is thickened. Sometimes the racemes are shortened to 1 or 2 joints 

 and borne on branches, the whole forming a panicle (as in Sorghum and 

 Sorghastrum) instead of a series of racemes. In a few genera the spikelets of 

 the pair are alike. In Trachypogon the fertile spikelet is pedicellate and the 

 sterile one nearly sessile. The most important economic plants in this tribe are 

 sugarcane and sorghum. 



Key to the genera of Andropogoneae 



la. Spikelets alike, all perfect. (See also Arthraxon and Sorghastrum in which pedicellate 

 spikelets are not developed.) 

 Spikelets surrounded by a copious tuft of soft hairs. 



Rachis continuous, the spikelets falling; the spikelets of the pair unequally pedicellate. 



Racemes in a narrow spikelike panicle ; spikelets awnless 148. Imperata. 



Racemes in a broad fan-shaped panicle; spikelets awned 149. Miscanthus. 



Rachis breaking up into joints at maturity with the spikelets attached; one spikelet 

 sessile, the other pedicellate. 



Spikelets awnless 150. Saccharum. 



Spikelets awned 151. Erianthus. 



Spikelets not surrounded by turfs of hairs; racemes few 152. Microstegium. 



lb. Spikelets unlike, the sessile perfect, the pedicellate sterile (sessile spikelet staminate, 

 pedicellate spikelet perfect in Trachypogon. 

 2a. Pedicel thickened, appressed to the thickened rachis joint (at least parallel to it) or 

 adnate to it; spikelets awnless, appressed to the joint. 



