20 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



Glumes not more than 1 cm. long, 1- to 5-nerved; spikelets not pendulous, 



Spikelets 3- to several-flowered, 1 to 1.5 cm. long 62. Helictotrichok. 



Spikelets 2-flowered (or 3-flowered in Trisetum cernuum), mostly less than 1 cm. 

 long. 

 Lemmas keeled, the awn when present from above the middle. 



Rachilla joints very short, glabrous or minutely pubescent; lemmas awnless 



or with a straight awn from a toothed apex 55. Koeleria. 



Rachilla joints slender, villous; lemmas with a dorsal bent awn (awnless or 



nearly so in 2 species) 57. Trisetum. 



Lemmas convex, awned from below the middle. 



Rachilla prolonged behind the upper floret; lemmas truncate and erose-dentate 

 at summit. 



Awn slender, not jointed 58. Deschampsia. 



Awn clavate, jointed near the middle 60. Corynephorus. 



Rachilla not prolonged; lemmas tapering into 2 slender teeth 59. Aira. 



TRIBE 5. AGROSTIDEAE 



Spikelets 1 -flowered, usually perfect, in open, contracted, or spikelike pan- 

 icles, but not in true spikes nor in 1-sided racemes. 



A large and important tribe, inhabiting more especially the temperate and 

 cool regions. The articulation of the rachilla is usually above the glumes, the 

 mature floret falling from the persistent glumes, but in a few genera the articu- 

 lation is below the glumes, the mature spikelet falling entire {Alopecurus, 

 Cinna, Polypogon, Lycurus, and Limnodea). The palea is small or wanting in 

 Alopecurus and in some species of Agrostis. In a few genera the rachilla is pro- 

 longed behind the palea as a minute bristle, or sometimes as a more pro- 

 nounced stipe {Brachyelytrum, Limnodea, Cinna, Gastridium, Calamagrostis, 

 Ammophila, Lagurus, Apera, and a few species of Agrostis). In some genera 

 the rachilla joint between the glumes and the lemma is slightly elongated, 

 forming a hard stipe which remains attached to the mature fruit as a pointed 

 callus. The callus is well marked in Stipa (especially in S. spartea and its 

 allies) and in Aristida, the mature lemma being terete, indurate, and con- 

 volute, the palea wholly enclosed. In many genera the lemma is awned either 

 from the tip or from the back, the awn being trifid in Aristida. 



Key to the genera of Agrostideae 



Glumes wanting. Low annual 73. Coleanthus. 



Glumes present (the first obsolete in Muhlenbergia schreberi and sometimes in Brachyelytrum 

 and Phippsia). 

 la. Articulation below the glumes, the spikelets falling entire. 



Spikelets in pairs in a spikelike panicle, one perfect, the other staminate or neuter, the 



pair falling together 78. Lycurus. 



Spikelets all alike. 



Glumes long-awned 77. Polypogon. 



Glumes awnless. 



Rachilla not prolonged behind the palea; panicle dense. 



Glumes united toward the base, ciliate on the keel; inflorescence not capitate 



and bracteate 76. Alopecurus. 



Glumes not united, glabrous; inflorescence capitate in the axils of broad bracts. 



85. Crypsis. 

 Rachilla prolonged behind the palea; panicle narrow or open, not dense; glumes 

 not united, not ciliate on the keel. 

 Panicle narrow; lemma with a slender bent twisted awn from the bifid apex. 



75. Limnodea. 

 Panicle open, drooping; lemma with a minute straight awn just below the entire 



apex (rarely awnless) 74. Cinna. 



lb. Articulation above the glumes. 



Fruit dorsally compressed, indurate, smooth, and shining, awnless 88. Milium. 



Fruit laterally compressed or terete, awned or awnless. 



2a. Fruit indurate, terete, awned, the nerves obscure; callus well developed, oblique, 

 bearded. 

 Awn trifid, the lateral divisions sometimes short, rarely obsolete (when obsolete no 



