326 CONTEIBUTIONS PEOM THE NATIONAL HERBARIUM. 



Spikelets not over 2.5 mm. long; first glume less than half 



the length of the spikelet 21. P. repens. 



Spikelets 3 to 7 mm. long (sometimes less than 3 mm. in 



P. virgatum cube'Tise) ; first glume more than half the 



length of the spikelet. 



Culms decumbent or creeping at base ; spikelets 3.2 to 4 



mm. long ; plants reedlilte, as much as 4 meters tall, 



gregarious ; Trinidad and Tobago 23. P. altum. 



Culms erect ; plants less than 2 meters tall, not gre- 

 garious. 

 Spikelets 4.3 to 5.5 mm. long, beaked. 



24. P. amarulum. 

 Spikelets not over 3.2 mm. long, not beaked. 



22. P. virgatum. cubense. 

 Plants not forming creeping scaly rhizomes. 



Fruit crested at the apex ; spikelets 5.5 to 6 mm. long ; 

 plants decumbent at base, forming a tangled mass. 



74. P. zizanioides. 

 Fruit not crested. 



Panicles narrow and few-flowered ; culms erect and 

 wiry; blades drying involute. (Teneka.) 

 Second glume and sterile lemma exceeding the fruit; 



spikelets pointed 25. P. tenerum. 



Second glume and sterile lemma not exceeding the 

 fruit ; spikelets rather blunt. 

 Pedicels bearing long stiff erect hairs at the sum- 

 mit ; Trinidad 27. P. caricoides. 



Pedicels not hairy. 



Spikelets attenuate at base, about 2 mm. long; 

 leaves more or less pilose; Trinidad. 



26. P. stenodoides. 

 Spikelets not attenuate at base, about 1.5 mm. 



long ; leaves glabi-ous 28. P. stenodes. 



Panicles open or contracted, many-flowered. 

 Panicles 40 to GO cm. long, the numeroiis elongate 



branches in verticils 49. P. megiston. 



Panicles mostly much less than 40 cm. long, the 

 branches not verticillate. 

 Spikelets short-pediceled along the nearly simple 

 panicle branches. 

 Plants stoloniferous, aquatic or subaquatic; culms 

 decumbent at base ; Trinidad 73. P. grande. 

 Plants not stoloniferous ; culms erect. 



29. P. condensum. 

 Spikelets long-pediceled ; panicle open at maturity. 

 First glume not pointed, two-thirds the length of 

 the spikelet or more; spikelets bluut. 

 Panicles not over 6 cm. long ; plants somewhat 

 glaucous, relatively small. (Pabvifolia.) 

 Culms very slender, decumbent or creeping; 

 blades 1 to 3 cm, long. 



43. P. parvifolium. 



