HITCHCOCK GRASSES OF CUBA. 187 



Spikelets unisexual; plants monoecious; blades abruptly contracted into 

 petiole-like bases. 



Inflorescence consisting of 2 slender racemes, one staminate the other 

 pistillate, digitate at the summit of a naked culm; leafy stems dis- 

 tinct from the base; plants low 44. Mniochloa (p. 233). 



Inflorescence borne on leafy culms; fruit bony-indurated. 



Fruit dorsally compressed; panicles terminal on culms or leafy 

 branches, pistillate spikelets above, staminate spikelets below in 



same panicle 42. Olyra (p. 233). 



Fruit laterally compressed, conspicuously gibbous on upper dorsum; 

 panicles all axillary or axillary and terminal, the terminal when 



present wholly staminate 43. Lithachne (p. 233). 



Spikelets all perfect. 



Spikelets 2 to 4 together sunken in the alternate notches of a broad, 



thickened rachis; creeping grasses 41. Stenotaphrum (p. 232). 



Spikelets not sunken in notches of a thickened rachis. 



Spikelets solitary or in small clusters subtended by an involucre 

 consisting of 1 to many bristles (sterile branches), these some- 

 times grown together. 



Involucre persistent on the axis, spikelets deciduous. 



36. Chaetochloa (p. 230). 

 Involucre deciduous with and attached to the spikelets. 

 Involucre a spiny bur inclosing 1 to 5 spikelets. 



37. Cenchrus (p. 231). 

 Involucre of distinct bristles. 



Involucre of a single sterile branch produced beyond 



each spikelet 40. Paraiheria (p. 232). 



Involucre of numerous often plumose bristles. 



38. Pennisetum (p. 232). 

 Spikelets not involucrate. 



Fruits not rigid, margins of lemma not inrolled. 



Inflorescence of slender racemes, divergently digitate at 

 the summit of the culm, both glumes wanting. 



18. Reimaroehloa (p. 198). 

 Inflorescence paniculate. 



Blades cordate-clasping, fruit open at summit; aquatic 



or semiaquatic grasses 29. Hymenachne (p. 212). 



Blades not cordate-clasping. 



Spikelets awned, first glume with a pedicel-like 



callus 39. Chaetium (p. 232). 



Spikelets awnless; fruits cartilaginous-indurated, 

 papillose, usually dark-colored, lemmas with 

 thin, usually white margins. 



Fruit open at the white-margined summit; 

 spikelets tuberculate-hispid between the 



nerves 21. Leptocoryphium (p. 207). 



Fruit not open nor white-margined at summit. 

 Sterile lemma like the fertile lemma in 



texture 26. Alloteropsis (p. 210). 



Sterile lemma like the glumes in texture. 

 Spikelets clothed with long silky 



hairs 25. Valota (p. 210). 



Spikelets glabrous or pubescent only. 



24. Syntherisma (p. 208). 



