326 American Midland Naturalist Monograph No. 7 



5. Glumes lanceolate to linear 19. Agropyron 



5. Glumes ovate 20. Triticum 



1. Spikelets 2-6 at each joint of the rachis. 



6. Spikelets 3 at each joint, 1-flowered, the lateral pair usually aborted; 



glumes awn-like 25. Hordeum 



6. Spikelets usually in pairs, 2- to 6-flowered. 



7. Spike loosely flowered, the spikelets widely spreading; glumes obso- 

 lete or bristle-like 24. Hystrix 



1. Spike densely flowered, the spikelets ascending; glumes well-developed 

 23. Elymus 



Tribe 4. Aveneae. — Oat Tribe 



1. Spikelets more than 5 mm long. 



2. Lemmas awned from the back, or awn absent. 



3. Spikelets more than 1 cm long; plants annual 31. Avena 



3. Spikelets less than 1 cm in length; lower floret long-awned, the upper 



one usually awnless; plants perennial 32. Arrhenatherum 



2. Lemmas awned from between the apical teeth 33. Danthonia 



1 . Spikelets not more than 5 mm long. 



4. Spikelets disarticulating above the glumes. 



5. Inflorescence contracted, spike-like; glumes unequal; plants of dry 

 habitats 27. Koeleria 



5. Inflorescence a spreading panicle; lemmas awned from the middle or 



below; plants of moist habitats. 

 6. Lemmas truncate and erose at summit 29. Deschampsia 



6. Lemmas 2-toothed at summit 30. Aira 



4. Spikelets disarticulating below the glumes. 



7. Florets awnless, all perfect; glumes exceeded by the upper floret 



28. Sphenopholis 



7. Lower spikelet perfect, awnless, the upper staminate and bearing a 



hooked awn: glumes longer than the florets 34. Holcus 



Tribe 5. Agrostideae. — Timothy Tribe 

 1. Lemmas of more delicate texture than the glumes, not at all indurated. 

 2. Inflorescence dense, spike-like; glumes keeled. 

 3. Lemma awnless. 



4. Glumes short-awned ; leaves flat 41. Phleum 



4. Glumes awnless. 



5. Tall perennials; florets bearing a tuft of hairs at base 



36. Ammophila 



5. Low annuals; florets without hairs at base 44. Heleochloa 



3. Lemma awned; glumes awnless 40. Alopecurus 



2. Inflorescence an open or somewhat spike-like panicle; glumes not keeled. 



6. Grain permanently enclosed in the lemma and palet; pericarp ad- 



herent to the grain. 



7. Palet 1-nerved, 1-keeled; stamen 1; tall perennials with Hat leaves 



and nodding panicles 39. Cinna 



1. Palet 2-ner\'ed and 2-keeled; stamens 3. 

 8. Lemma with long hairs at the base. 



9. Lemma and palet membranous; rachilla prolonged beyond the 



palet, bristle-like 35. Calamagrostn 



9. Lemma and palet chartaceous; rachilla not prolonged beyond 

 the palet 37. Calamovilfa 



