GENERA OF GRASSES OF THE UNITED STATES. 13 
Key to the genera of Aveneae. 
Ja. Spikelets awnless or the upper lemma mucronate (rarely short-awned 
REBIIAS PREVETYO TO MOLIS)) pee toe 8 Sh a ae le 2 
2a. Articulation below the glumes; glumes distinctly different in 
shape, the second widened above____-____=---___ 46. SPHENOPHOLIS. 
2b. Articulation above the glumes; glumes similar in shape. 44. Kor erra. 
1b. Spikelets awned (awnless in Trisetum wolfii) _----_______________- 3 
3a. Florets 2, one perfect, the other staminate__________________ 4 
4a. Lower floret staminate, the awn twisted, geniculate, ex- 
EST Cs C0 eae se NE eee 48. ARRHENATHERUM. 
4p. Lower floret perfect, awnless; awn of upper floret hooked. 
; 51. NoTHoLcus. 
3b. Florets 2 or more, all alike except the reduced upper ones_____- 5 
da. Awn arising from between the teeth of a bifid apex, flat- 
tened, twisted ; inflorescence a simple panicle or reduced 
to a raceme or even to a single spikelet-_______ 52. DANTHONTA. 
5b. Awn dorsal, not flattened ; lemma often bifid at apex________ - 6 
6a. Spikelets large, the glumes over 1 cm. long________ 47. AVENA. 
Gb= Spikelets,less sthan, tem. Jong 28s 7 
7a. Lemmas keeled, bidentate; awn arising from above 
Pew ALG MG pest ea a sn ee 45, TRISETUM. 
7b. Lemmas convex; awn from below the middle______ 8 
8a. Rachilla prolonged behind the upper floret; lem- 
mas truncate and erose-dentate at summit__ 49. Arra. 
8b. Rachilla not prolonged; lemmas tapering into 2 
SLEMders ‘tEe@t His x eer a eee Pe Sy ee ein 50. ASPRIS. - 
TrIBE 5, AGROSTIDEAE. 
Spikelets 1-flowered, usually perfect, arranged in open, contracted, 
or spikelike panicles, but not in true spikes nor in one-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 Agrostis. In a few genera the rachilla is prolonged 
behind the palea as a minute bristle, or sometimes as a more pro- 
nounced villous stipe (Brachyelytrum, Limnodea, Cinna, three species 
of Agrostis, Gastridium, Calamagrostis, Ammophila, and Lagurus). 
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 convolute, the palea wholly 
inclosed. In many genera the lemma is awned either from the tip 
or from the back, the awn being trifid in Aristida. 
