MANUAL OF THE GRASSES OF THE UNITED STATES 23 



2b. Spikelets with 1 or more modified florets above the perfect one. 



Spikelets with 2 sterile florets below the perfect one; second glume bearing a squarrose 



spine on the back; spike single, arcuate 108. Ctenium. 



Spikelets with no sterile florets below the perfect one; second glume without a 

 squarrose spine. 

 Spikes digitate or nearly so. 



Fertile lemma 1-awned or awnless 110. Chloris. 



Fertile lemma 3-awned 111. Trichloris. 



Spikes racemose along the main axis. 



Spikelets distant, appressed; spikes slender, elongate 109. Gymnopogon. 



Spikelets approximate or crowded, not appressed ; spikes usually short and rather 

 stout. 

 Spikelets 3 in each spike, the 2 lateral staminate or rudimentary; spikes falling 



entire 113. Cathestecum. 



Spikelets 2 to many (rarely 1) in each spike, all alike; spikes falling entire or 

 persistent, the florets falling 112. Bouteloua. 



TRIBE 8. PHALARIDEAE 



Spikelets with 1 perfect terminal floret and, below this, a pair of staminate 

 or neuter florets (1 sometimes obsolete in Phalaris). 



A small tribe of about 6 genera, 4 of which are found in the United States. 

 In Phalaris the lower florets are reduced to minute scalelike lemmas closely 

 appressed to the edges of the fertile floret. In Hierochloe the lateral florets are 

 staminate and as large as the fertile floret. 



Key to the genera of Phalarideae 



Lower florets staminate; spikelets brown, shining 116. Hierochloe. 



Lower florets neuter; spikelets green or yellowish. 



Lower florets consisting of awned hairy sterile lemmas exceeding the fertile floret. 



117. Anthoxanthum. 



Lower florets reduced to small awnless scalelike lemmas, much smaller than the fertile 



florets 118. Phalaris. 



TRIBE 9. ORYZEAE 



Spikelets 1-flowered, perfect, strongly laterally compressed, paniculate; 

 glumes reduced or wanting; palea apparently 1-nerved; stamens 6. 



A small tribe whose affinities are not evident. It includes rice, the im- 

 portant food plant. 



Key to the genera of Oryzeae 



Glumes minute; lemma often awned 119. Oryza. 



Glumes wanting; lemma awnless 120. Leersia. 



TRIBE 10. ZIZANIEAE 



Spikelets unisexual, the pistillate terete or nearly so; glumes shorter than 

 the lemma, usually 1 or both obsolete, the pedicel disarticulating below the 

 spikelet. Glumes well developed in Pharus, a tropical genus placed in this 

 tribe provisionally. 



A small tribe of uncertain affinities, aquatic or subaquatic grasses (except 

 Pharus) of no economic importance except the Indian rice (Zizania) . 



Key to the genera of Zizanieae 



Blades elliptic, 2 to 4 cm. wide 125. Pharus. 



Blades much longer than wide. 



Culms slender; plants low; staminate and pistillate spikelets borne in separate inflores- 

 cences. 



Inflorescence a few-flowered raceme; floating aquatic 124. Hydrochloa. 



Inflorescence a panicle; plants stoloniferous 123. Luziola. 



Culms robust; plants tall; staminate and pistillate spikelets borne in the same panicle. 

 Pistillate spikelets on the ascending upper branches, the staminate on the spreading 



