MANUAL OF THE GRASSES OF THE UNITED STATES 25 



lb. Spikelets with only 1 perfect floret, often with additional imperfect florets 

 above or below. 

 2a. Spikelets without additional modified florets, the rachilla sometimes 

 prolonged. 

 Rachilla articulate below the glumes, the spikelets falling entire. 



Glumes unequal, narrow 99. Spartina. 



Glumes equal, broad, boat-shaped 98. Beckmannia. 



Rachilla articulate above the glumes. 



Spikes digitate; rachilla prolonged 95. Cynodon. 



Spikes racemose along the main axis; rachilla not prolonged. 



Spikes slender, divaricate, the main axis elongating and becoming 



loosely spiral in fruit 97. Schedonnardus. 



Spikes short and rather stout, appressed, the axis unchanged in fruit. 



96. Willkommia. 

 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. 



100. Ctenium. 

 Spikelets with no sterile florets below the perfect one; second glume 

 without a squarrose spine; spikes usually several. 

 Spikes digitate or nearly so. 



Fertile lemma 1-awned or awnless 102. Chloris. 



Fertile lemma 3-awned 103. Trichloris. 



Spikes racemose along the main axis. 



Spikelets distant, appressed; spikes slender, elongate. 



101. 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 105. Cathestecum. 



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

 falling entire or persistent, the florets falling. 



104. Bouteloua. 



TRIBE 8. PHALARIDEAE 



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

 staminate or neuter florets (one sometimes obsolete in Phalaris). 



A small tribe of about six genera, only three 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 and shining 108. Hierochloe. 



Lower florets neuter; spikelets green or yellowish. 



Lower florets reduced to small awnless scalelike lemmas; spikelets much 



compressed laterally 110. Phalaris. 



Lower florets consisting of awned hairy sterile lemmas exceeding the fertile 

 floret; spikelet subterete 109. Anthoxanthum. 



TRIBE 9. ORYZEAE 



Spikelets 1 -flowered, perfect, strongly laterally compressed, pani- 

 culate; glumes reduced or wanting; palea apparently 1-nerved; 

 stamens 6. 



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

 the important food plant. 



Key to the genera of Oryzeae 



Glumes minute; lemma often awned 111. Oryza. 



Glumes wanting; lemma awnless 112. Leersia. 



