GRASSES OF OHIO 269 



35. Lemma broad, glabrous, its awn deciduous J callus short, obtuse. 



Oryzopsis (47) 



35. Lemma narrow; its awn persistent; callus usually acute. Stipa. I 18) 



36. Spikelets with a terminal perfect flower and 2 staminate lateral flowers. 



S avast ana. (50) 



36. Spikelets with but 1 flower and sometimes with mere vestiges of lateral 

 flowers. 37 



37. Empty glumes very unequal; stamens 2; third and fourth glumes (above the 

 two empty glumes) awned upon the back. Antlwxantluim. (52) 



37. Empty glumes equal ; stamens 3 ; third and fourth glumes small and ves- 

 tigial not awned. Phalaris. <"-i I 



—38— 



38. Spikelets monecious, the staminate and carpellate spikelets in different parts 

 of the inflorescence. 39 



38. Spikelets not monecious; staminate spikelets if present distributed among the 

 perfect ones. 40 



39. Staminate and carpellate spikelets much alike in appearance, intermixed in 

 the panicle, but the staminate at the top of the branches. Zizaniopsis. 



39. Staminate spikelets in the lower part of the panicle; the carpellate above, 

 unlike in appearance. Zizania. (61) 



40. Inflorescence a compact spike-like panicle. 41 



40. Inflorescence a loose panicle or with slender branches. 42 



41. With an involucre of bristles about the base of the spikelets. 



Chaetochloa (58) 



41. Spikelets without' a subtending involucre of bristles. Alopccurus. (41) 



42. Spikelets laterally compressed. 43 



42. Spikelets round, or dorsally compressed. 45 



43. Spikelets 2-3-flowered; empty glumes dissimilar. Sphenopholis. (8) 



43. Spikelets 1-flowered. 44 



44. Glumes 4; lemma with a short awn between the bifid apex. China. (39) 



44. Glumes only 2, without awns. Homaloccnchms. (60) 



45. Flowering glumes chartaceous or coriaceous, differing from the membranous 

 empty glumes. 46 



45. Flowering glumes thin and hyaline, usually much more delicate than the 

 empty glumes. 48 



46. Margins of the fruiting flowering glumes hyaline and flat. Leptoloma. (54) 



46. Margin of the fruiting lemma inrolled and not hyaline. 47 



47. Sterile lemma awned or pointed; spikelets crowded in 1-sided racemes which 

 are arranged in a panicle. Echinochloa. (56) 



47. Empty glumes and lemmas awnless; spikelets usually in panicles. Panicum (53 ) 



48. Stem solid. 49 



48. Stem hollow. 50 



49. Sessile spikelets perfect the stalked spikelet vestigial, spikelets on the ends 

 of slender branches of a spreading panicle. Holcus. (62) 



49. Spikelets all perfect; arranged in pairs along the continuous branches of the 

 panicle. Miscanthus. (64) 



50. Lemma with a hooked dorsal awn, spikelets in a loose panicle: plant softly 

 pubescent. Notho holcus. (21) 



50. Lemma with a prominent terminal awn; spikelets in a slender panicle: leaves 

 scabrous and glaucous, the sheaths smooth. Sorghastrum. I 63 > 



—51— 



51. Spikelets not covered with a prickly bur. 52 



51. Spikelets covered with a prickly bur. Cenchrus. (59) 



