GENERA OF GRASSES OF THE UNITED STATES. 



Key to the genera of Festuceae. 



la. Plants dioecious, the sexes very dissimilar, the pistillate lemmas with 

 3 long twisted divergent awns, the staminate lemma awnless 



or mucronate 30. SCLEROPOGON. 



Ib. Plants with perfect flowers, or, if dioecious, the sexes not dissimilar 



in appearance 2 



2a. Lemmas divided at the summit into 5 to several awns or awn- 

 like lobes 3 



,>;i. Awnlike lobes 5 ; inflorescence a simple erect raceme. 29. ORCUTTIA. 



3b. Awns 9 or more 4 



4a. Awns unmixed with awned teeth ; all the florets falling 



attached, their awns forming a pappuslike crown, only 

 the lowest floret fertile ; panicles narrow. 32. PAPPOPHOBUM. 

 4b. Awns mixed with awned teeth; florets not falling at- 

 tached, the rachilla disarticulating between them; 



panicles somewhat open 31. COTTEA. 



2b. Lemmas awnless, with a single awn, or, if 3, the lateral awns 



minute 5 



5a. Tall stout reeds with large plumelike panicles; lemmas or 



rnchilla with long silky hairs as long as the lemmas G 



Ga. Lemmas hairy; rachilla naked 19. ARUNDO. 



Gb. Lemmas naked; rachilla hairy 20. PHRAGMITES. 



5b. Low or rather tall grasses, rarely over 5 feet tall 7 



7a. Plants dioecious, perennial; lemmas glabrous; grasses 



of salt or alkaline soils 8 



8a. Plants low and creeping; spikelets obscure, scarcely 

 differentiated from the short crowded rigid 



leaves 16. MONANTHOCHLOE. 



Sb. Plants erect from creeping rhizomes; spikelets in a 



narrow simple exserted panicle 17. DTSTICHLIS. 



7b. Plants not dioecious (except in a few species of Poa with 



villous lemmas and in an annual species of Eragrostis) _ 9 



9a. Spikelets of two forms, sterile and fertile intermixed ; 



panicle dense, somewhat one-sided 10 



lOa. Fertile spikelets 2 or 3 flowered ; sterile spike- 

 lets with numerous rigid awn-tipped glumes; 



panicle dense and spikelike 22. CYNOSTJRTTS. 



lOb. Fertile spikelets with 1 perfect floret, long- 

 awned ; sterile spikelets with many obtuse 

 glumes ; panicle branchlets short, nodding. 



23. ACHYRODES. 



9b. Spikelets all alike in the same inflorescence 11 



lla. Lemmas 3-nerved, the nerves prominent, often 



hairy 12 



12a. Inflorescence a few-flowered head or capi- 

 tate panicle overtopped by the leaves or 

 partly concealed in them ; lemmas toothed 

 or cleft ; low plants of the arid regions, _ 13 

 13a. Inflorescence hidden among the sharp- 

 pointed leaves, not woolly; plants 



annual (Chlorideae) 97. MUNROA. 



13b. Inflorescence a capitate woolly panicle, 



not concealed ; plants perennial 14 



