43. Caryopsis not falling from the lemma and palea, remaining permanently en- 



closed in them; seed adnate to the pericarp 33. Muhlenbergia 



44(34). Glumes as long as the lowest floret, usually as long as the spikelet 

 (sometimes shorter in Sphenopholis) ; lemmas awned from the back 

 (spikelets awnless in species of Trisetum and Sphenopholis) (45) 



44. Glumes shorter than the first floret (except in Tridens strictus); lemmas awn- 



less or awned from the tip or from a bifid apex (50) 



45(44). Florets 2, one perfect, the other staminate 24. Holcus 



45. Florets 2 or more, all alike except the reduced upper ones (46) 



46(45). Articulation below the glumes, the spikelets falling entire (47) 



46. Articulation above the glumes, the glumes similar in shape (48) 



47(46). Lemmas (at least the upper) with a conspicuous bent awn; glumes 

 nearly alike 22. Trisetum 



47. Lemmas awnless or the upper with a short awn; second glume much wider 



than the first 21. Sphenopholis 



48(46). Lemmas bind at apex, awned or mucronate between the lobes; spikelets 

 several-flowered 25. Danthonia 



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



(49) 



49(48). Lemmas keeled, the awn when present from above the middle 



22. Trisetum 



49. Lemmas convex, awned from below the middle 23. Deschampsia 



50(44). Tall stout reeds with large plumelike panicles; lemmas and rachilla with 

 long silky hairs as long as the lemmas (51 ) 



50. Low or rather tall grasses, rarely more than 1.5 m. tall; panicles not as above 



(52) 



51(50). Lemmas naked; rachilla hairy 14. Phragmites 



51. Lemmas hairy; rachilla naked 13. Arundo 



52(50). Plants dioecious, perennial (53) 



52. Plants not dioecious (except in the annual Eragrostis reptans) (54) 



53(52). Plants low, stoloniferous; spikelets obscure, scarcely differentiated from 

 the short crowded rigid leaves 9. Monanthochloe 



53. Plants erect from creeping rhizomes; spikelets in narrow simple exserted 



panicles 10. Distichlis 



54(52). Lemmas 3-nerved, the nerves prominent, often hairy (55) 



54. Lemmas 5- to many-nerved, the nerves sometimes obscure (57) 



55(54). Inflorescence a few-flowered head or capitate panicle overtopped by the 

 leaves or partly concealed in them; lemmas toothed or cleft; low 

 plants of usually arid regions 15. Tridens 



55. Inflorescence an exserted open or spikelike panicle (56) 



56(55). Lemmas pubescent on the nerves or callus, the midnerve usually exserted 

 as an awn or mucro 15. Tridens 



56. Lemmas not pubescent on the nerves nor callus (the internerves sometimes 



pubescent), awnless 8. Eragrostis 



57(54). Spikelets with 1 to 4 empty lemmas below the fertile florets; nerves ob- 

 scure; lemmas firm 11. Chasmanthium 



57. Spikelets with no empty lemmas below the fertile florets; nerves usually 



prominent; lemmas membranous (firm in a few species of Bromus 

 and Festuca) (58) 



173 



