22 MISC. PUBLICATION 200, u. s. DEPT. OF AGRICULTURE 



Spikelets 1 cm or more long; awns conspicuous, flat, bent. 



60. DANTHONIA. 

 Spikelets not more than 5 mm long; awns minute or nearly obsolete. 



51. SCHISMUS. 

 Spikelets 2-flowered, sometimes with a rudimentary third floret. 



Spikelets large, the glumes more than 1 cm long 57. AVENA. 



Spikelets 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. 



52. KOELERIA. 

 Rachilla joints slender, yillous; lemmas with a dorsal bent awn 



(awnless or nearly so in 2 species) 54. TRISETUM. 



Lemmas convex, awned from below the middle. 



Rachilla prolonged behind the upper floret; lemmas truncate and 



erose-dentate at summit 55. DESCHAMPSIA. 



Rachilla not prolonged; lemmas tapering into 2 slender teeth. 



56. AIRA. 

 TRIBE 5. AGROSTIDEAE 



Spikelets 1-flowered, usually perfect, in open, contracted, or spike- 

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



A large and important tribe, inhabiting more especially the tem- 

 perate 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 articulation is below the glumes, the mature 

 spikelet falling entire (Alopecurus, Cinna, Polypogon, Lycurus, and 

 Limnodea). The palea is small or wanting in some species of Agros- 

 tis. In a few genera the rachilla is prolonged behind the palea as a 

 minute bristle, or sometimes as a more pronounced stipe (Brachyely- 

 trum, Limnodea, Cinna, Gastridium, Calamagrostis , Ammophila, 

 Lagurm, 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, in- 

 durate, and convolute, 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 66. 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 71. LYCURUS. 



Spikelets all alike. 



Glumes long-awned 70. POLYPOGON. 



Glumes awnless. 



Rachilla not prolonged behind the palea; panicle dense, spikelike; 

 glumes united toward the base, ciliate on the keel. 



69. ALOPECURUS. 

 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 68. LIMNODEA. 



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



the entire apex (rarely awnless) 67. CINNA. 



Ib. Articulation above the glumes. 



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



81. MILIUM. 



