48 American Midland Naturalist Monograph No. 2 



5. Spikelels usually in pairs, 2-6-flowered. 



6. Spike loosely flowered, the spikelets widely spreading; glumes obsolete or bristle- 

 like 19. Hvstrix 



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



18. Elvmus 



Tribe 4. Aveneae. — Oat Tribe 



1. Spikelets more than 5 mm. long. 

 2. Lemmas awned from the back. 



3. Spikelets more than I cm. long; plants annual 25. Avena 



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

 usually awnless ; plants perennial 26. Arrhenatherum 



2. Lemma awned from between the apical teeth 27. Danlhonia 



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 



22. Koeleria 



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



plants of moist habitats 24. Deschampsia 



4. Spikelets disarticulating below the glumes. 



6. Florets awnless, all perfect; glumes exceeded by the upper floret. .23. Sphenopholis 

 6. Lower spikelet perfect, awnless, the upper staminafe and bearing a hooked awn ; 



glumes longer than the florets 28. Holcus 



Tribe 5. Agrostideae. — Timothy Tribe 



1. Lemma 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 35. Phleum 



4. Glumes awnless. 



5. Tall perennials; florets bearing a tuft of hairs at base 30. Ammophila 



5. Low annuals; florets without hairs at base 38. Hcleochloa 



3. Lemma awned; glumes awnless 34. Alopecurus 



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



6. Grain permanently enclosed in the lemma and palet; pericarp adherent to the 

 gram. 

 7. Palet 1 -nerved, 1 -keeled; stamen I ; tall perennials with flat leaves and nodding 

 panicles 33. Cinna 



7. Palet 2-nerved 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 29. Calamagroslis 



9. Lemma and palet chartaceous; rachilla not prolonged beyond the palet 



3 1 . CalamovUfa 



8. Lemma without a tuft of hairs at the base. 



10. Lemma with a terminal awn. or mucronate at apex 36. Muhlenbergia 



10. Lemma awnless or with a dorsal awn 32. Agrosiis 



6. Grain not permanently enclosed in the lemma and palet, readily separating from 

 the pericarp 37. Sporobolus 



1 . Lemma indurated when mature, closely enveloping the grain. 



1 1 . Lemma awnless 40. Milium 



1 1 . Lemma awned. 



12. Lemma 3-awned 43. AristiJa 



