MANUAL OF THE GRASSES OF THE UNITED STATES 19 



Lemmas awned; florets lateral to the rachis 53. Scribneria. 



Lemmas awnless; florets dorsi ventral to the rachis. 



First glume wanting 51. Monerma. 



First glume present, the pair standing in front of the spikelet 52. Parapholis. 



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 50. Lolium. 



Spikelets placed flatwise to the rachis. 



Plants perennial 42. Agropyron. 



Plants annual. 



Spikelets turgid or cylindric _ 44. Aegilops. 



Spikelets compressed. 



Glumes ovate, 3-nerved 43. Triticum. 



Glumes subulate, 1-nerved 45. Secale. 



lb. 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 re- 

 duced to awns 49. Hordeum. 



Spikelets 2 or more (sometimes solitary in Elymus) at each node of the rachis, alike, 2- to 

 6-flowered. 

 Glumes wanting or reduced to 2 short bristles; spikelets horizontally spreading or 



ascending at maturity. Spikes very loose 48. Hystrix. 



Glumes usually equaling the florets (reduced in Elymus interrupt us) ; spikelets appressed 

 or ascending. 

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



46. Elymus. 



Rachis disarticulating at maturity; glumes subulate, extending into long awns, these 



and the awns of the lemmas making the spike very bristly 47. Sitanion. 



TRIBE 4. AVENEAE 



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

 racemes (solitary in Danihonia 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 Air a and Holcus). 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 Sphenopholis are placed in this tribe because they 

 appear to be closely allied to Trisetum with which they agree in having oblan- 

 ceolate 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.... 63. Arrhenatherum. 



Lower floret perfect, awnless; upper floret awned 64. 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. 



57. Trisetum. 

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



wider than the first 56. Sphenopholis. 



Articulation above the glumes, the glumes similar in shape. 



Lemmas bifid at apex, awned or mucronate between the lobes. Spikelets several- 

 flowered. 



Awns conspicuous, flat, bent. Spikelets 1 cm. or more long 66. Danthonia. 



Awns minute or nearly obsolete. 



Spikelets 8 to 12 mm. long 65. Sieglingia. 



Spikelets not more than 5 mm. long; awns, when present, slender, rounded. 



54. Schismus. 

 Lemmas toothed, but not bifid and awned or mucronate between the lobes. 



Glumes 2 to 3.5 cm. long, 7- to 9-nerved; spikelets 2-flowered, or with a rudimentary 

 third floret, pendulous. Plants annual 61. Avena. 



