326 CONTRIBUTIONS FROM 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 cubense) ; first glume more than half the 
length of the spikelet. 
Culms decumbent or creeping at base; spikelets 3.2 to 4 
mm. long; plants reedlike, 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. (TrENERA.) 
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 inm. 
long; leaves glabrous_______ 28. P. stenodes, 
Panicles open or contracted, many-flowered. 
Panicles 40 to 60 cm. long, the numerous elongate 
branches in verticils__-________ 49. P. megiston. 
Panicles mostly much less than 40 em. 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 blunt. 
Panicles not over 6 cm. long; plants somewhat 
glaucous, relatively small. (PARVIFOLIA. ) 
Culms very slender, decumbent or creeping ; 
blades 1 to 3 cm. long. 
43. P. parvifolium. 
