MANUAL OF THE GRASSES OF THE UNITED STATES 21 



Lemmas awned; florets lateral to the rachis 50. SCRIBNERIA. 



Lemmas awnless; florets dorsiventral to the rachis. 



First glume wanting 48. LEPTURUS. 



First glume present, the pair standing in front of the spikelet. 



49. PHOLIURUS. 

 2b. Spikelets 2- to several-flowered, not sunken in the rachis. 



Spikelets placed edgewise to the rachis. First glume wanting except in the 



terminal spikelet 47. LOLIUM. 



Spikelets placed flatwise to the rachis. 



Plants perennial 39. AGROPYRON. 



Plants annual. 



Spikelets turgid or cylindric 41. AEGILOPS. 



Spikelets compressed. 



Glumes ovate, 3-nerved 40. TRITICUM. 



Glumes subulate, 1-nerved 42. SECALE. 



Ib. Spikelets more than 1 at each node of the rachis (solitary in part of the spike 



in some species of Elymus}. 

 Spikelets 3 at each node of the rachis, 1-flowered, the lateral pair pediceled, 



usually reduced to awns 46. HORDEUM. 



Spikelets 2 at each node of the rachis, alike, 2- to 6-flowered. 



Glumes wanting or reduced to 2 short bristles; spikelets horizontally spread- 

 ing at maturity. Spikes very loose 45. HYSTRIX. 



Glumes usually equaling the florets (reduced in Elymus interruptus) ; spikelets 



appressed or ascending. 

 Rachis continuous (rarely tardily disarticulating) ; glumes broad or narrow, 



entire 43. ELYMUS. 



Rachis disarticulating at maturity; glumes subulate, extending into long 

 awns, these and the awns of the lemmas making the spike very 

 bristly 44. SITANION. 



TRIBE 4. AVENEAE 



Spikelets 2- to several-flowered in open or contracted panicles, 

 or rarely in racemes (solitary in Danthonia unispicata) ; glumes usually 

 as long as or longer than the first lemma, commonly longer than all the 

 florets; lemmas usually awned from the back or from between the 

 teeth of a bifid apex, the awn usually bent, often twisted, the callus 

 and rachilla joints usually villous. 



A rather small tribe widely distributed in both warm and cool 

 regions. In our genera the rachilla is prolonged beyond the upper 

 floret as a slender stipe (except in Aim). The lemma is awnless or 

 nearly so in Schismus, two species of Trisetum, one species of Koeleria, 

 and in most of the species of Sphenopholis. Koeleria and Spheno- 

 pholis are placed in this tribe because they appear to be closely allied 

 to Trisetum with which they agree in having oblanceolate glumes 

 about as long as the first floret. 



Key to the genera of Aveneae 



Florets 2, one perfect, the other staminate. 



Lower floret staminate, the awn twisted, geniculate, exserted. 



58. ARRHENATHERUM. 



Lower floret perfect, awnless; upper floret awned 59. HOLCUS. 



Florets 2 or more, all alike except the reduced upper ones. 

 Articulation below the glumes, the spikelets falling entire. 



Lemmas, at least the upper, with a conspicuous bent awn; glumes nearly 



alike 54. TRISETUM. 



Lemmas awnless or (in S. pollens) the upper with a short awn; second glume 



much wider than the first 53. SPHENOPHOLIS. 



Articulation above the glumes, the glumes similar in shape. 



Spikelets several-flowered. Lemmas bifid at apex, awned or mucronate 

 between the lobes. 



