GRASS FAMILY 85 



Glumes not conspicuously compressed. 



Pericarp loosely enclosing the seed ; inflorescence an open panicle . . 20. Sporobolus. 

 Pericarp adherent to the seed; inflorescence open or contracted. 



Glumes long-awned 22. Polypogon. 



Glumes awnless, or short-awnod. 



Inflorescence a long slender dense spike-like panicle 21. Epicampes. 



Inflorescence often contracted but not conspicuously elongated. 



Palea l-nerved, or apparently so 23. Cinna. 



Palea plainly 2-nerved (sometimes nerveless or wanting). 



Glumes pliunose-ciliate ; inflorescence an ovoid head 28. Lagdrus. 



Glumes not plumose. 



Glumes saccate at base, much longer than the lemmas. .25. Gastridium. 

 Glumes not saccate at base. 



Rachilla not prolonged behind the palea (except in A. thurberiana) ; 

 callus hairs short or none (except in A. hallii) . . . .24. Agrostis. 

 Rachilla prolonged behind the palea as a usually hairy bristle. 



Lemma awned from the back; callus hairs long 



26. Calamagrostis. 



Lemma avrnless; callus hairs short 27. Ammophila. 



Tribe VI. Aveneae. Spikelets 2 to several-flowered, in open or contracted panicles; rachilla 

 prolonged behind the uppermost floret (except in Aira) ; glumes usually longer than the 

 first floret; 1 or more of the lemmas awned on the back or from the teeth of the bifid 

 apex (usually awnless in Koeleria and Sphenopholis) ; callus and usually the rachilla 

 joints hairy. 



Rachilla not prolonged; spikelets 2-flowered, perfect 30. Aira. 



Rachilla prolonged behind the uppermost floret ; spikelets 2 to several-flowered. 



Articulation below the glumes, the spikelets falling entire or the glumes and lowest 

 florets together. 



Glumes much exceeding the 2 florets; spikelet awned 29. Notholcu.s. 



Glumes exceeded by the upper floret; spikelet awnless 33. Sphenopholis. 



Articulation above the glumes. 



Awns wanting or but a mueronate tip 34. Koeleria. 



Awns present. 



Awns from between the teeth of the bidentate apex of the lemma, flattened, twisted. 



36. Danthonia. 

 Awns dorsal, not flattened. 



Lemmas more than % inch long 35. Avena. 



Lemmas less than % inch long. 



Lemmas keeled; awn from above the middle 32. Tbisetum. 



Lemmas convex; awn from below the middle 31. Deschampsia. 



Tribe VII. Chlorideae. Spikelets 1 to several-flowered, sessile in 1-sided spikes; spikes 

 digitate or racemose; lemma awnless or awned from between teeth; spikelets usually 

 compressed and closely imbricated (more distant and often slightly pediceled in Lep- 

 tochloa). 

 Spikes digitate. 



Plants perennial, extensively creeping 37. Cynodon. 



Plants annual, more or less spreading but not creeping. 



Perfect florets 2 or more, awnless 42. Eleusine. 



Perfect floret 1 (long-awned) 39. Chloris. 



Spikes racemose. 

 Spikelets 1-flowered. 



Glumes narrow, unequal 38. Spartina. 



Glumes broad, boat-shaped, equal 41. Beckmannia. 



Spikelets with more than 1 floret. 



Lemmas 3-awned; spikelets imbricated, with only 1 perfect floret 40. Bouteloua. 



Lemmas 1-awned or awnless; spikelets somewhat distant, with 3 to several perfect 



florets 43. Leptochloa. 



Tribe VIII. Festuceae. Spikelets 2 to many-flowered, pedicellate in racemes or in open or 

 contracted panicles (spikes in Orcuttia; solitary in Monanthochloe) ; glumes usuallj 



