FLOWERING PLANTS AND FERNS OF ARIZONA 81 



39. Lemmas variously lobed or dentate, 3-awned; spikelets 



with one perfect floret and 1 or 2 rudimentary florets 

 above it 56. Bouteloua. 



38. Spikes digitate or aggregate on a very short axis (40j. 



40. Lemmas awnless; rachis prolonged beyond the spike- 



lets in a naked point 50. Dactyloc texium. 



40. Lemmas awned (41). 



41. Lemmas 1 -awned: spikes digitate 54. Chloris. 



41. Lemmas 3-awned: spikes aggregate on a very short 



axis, but scarcely digitate 55. Trichloris. 



26. Spikelets in open or spikelike panicles (42). 

 42. Spikelets 1 -flowered: Tribe Agrostideae (43). 



43. Fruit indurate, terete, awned; callus well developed, oblique, 

 bearded (44). 

 44. Awn trifid, the lateral awns sometimes minute. 



45. Aristida. 

 44. Awn simple, with a distinct line of demarcation between 

 lemma and awn (45). 

 45. Awn readily deciduous, straight or sometimes bent but 



not tightly twisted 42. Oryzopsis. 



45. Awn persistent, twice geniculate, at least the lower seg- 

 ment tightly twisted (46). 

 46. Edges of the lemma not meeting, exposing the palea, this 

 projecting from the summit as a minute point ; callus 



short, acute 43. Piptochaetium. 



46. Edges of the lemma overlapping, enclosing the palea; 

 callus sharp pointed, usually acuminate, _ 44. Stipa. 

 43. Fruit thin or firm but not indurate; callus not well developed 

 (47). 

 47. Callus bearded (48). 



48. Lemma membranaceous, awned from the back. 



32. Calamagrostis. 



48. Lemma firm, chartaceous, awnless 33. Calamovilfa. 



47. Callus not bearded (49). 



49. Panicles narrow, dense, spikelike (50). 



50. Spikelets in pairs, 1 perfect, the othc-r staminate or 



neuter, the pair falling together S7= . Lycurus. 



50. Spikelets all alike, not paired (51). 



51. Glumes equal, similar, united at base, enclosing the 

 floret; articulation below the glumes, the spikelets 

 falling entire (52). 

 52. Glumes abruptly awned, hispid-ciliate on the keels. 



38. Phleum. 



52. Glumes awnless, pubescent or villous but not hispid- 



ciliate on the keels 35. Alopecurus. 



51. Glumes unequal, dissimilar, not united at base; artic- 

 ulation above the persistent glumes (53). 



53. Lemma awned from the tip or mucronate, 3-nerved. 



39. Muhlexbergia. 



53. Lemma awnless, 1-nerved 40. Sporobolu>. 



49. Panicles open or dense but scarcely spikelike, except in 



Polypogon monspeliensis with long-awned glumes (54). 



54. Glumes longer than the lemma; lemma and palea much 



thinner than the glumes (55). 



55. Glumes awnless; palea much shorter than the lemma, 



sometimes reduced to a small nerveless scale. 



34. Agrostis. 



55. Glumes long-awned: palea nearly as long as the lemma. 



36. PoLYPOGOX. 



54. Glumes shorter than the lemma, or the awn tips exceeding 

 the lemma in Muhlenbergia racemosa 



56. Lemma densely pubescent on the nerves. 



41. Blepharoxeurox. 

 56. Lemma glabrous or, if pubescent, then not densely so 

 on the nerves 

 57. Lemma awned from the tip or mucronate, 3-nerved. 



39. Muhlenbergia. 

 57. Lemma awnless, 1-nerved 40. Sporobolus. 



