324 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Basal leaves similar to culm leaves, not forming a winter rosette; spikelets 

 all fertile. 

 Spikelets piano-gibbous, the second glume swollen, bristly and burlike at 

 maturity ; first glume nearly as long as the minute spikelet ; Trinidad. 



75. P. hirtum. 

 Spikelets not piano-gibbous nor burlike. 

 Fruit transversely rugose. 

 Plants perennial. 



Spikelets relatively long-pediceled in a large open panicle. 



20. P. maximum. 

 Spikelets subsessile along the racemes or raceme-like branches of 

 the panicle. 

 Nodes bearded ; inflorescence of numerous long sublasciculate 



ascending racemes 5. P. barbinode. 



Nodes glabrous ; inflorescence of several short erect racemes. 



4. P. geminatum. 

 Plants annual. ( Fasctculata. ) 

 Spikelets glabrous. 



Spikelets not over 2 mm. long, not reticulate-veined 6. P. reptans. 



Spikelets 2 to 3 mm. long, strongly reticulate-veined. 



7. P. f asciculatum. 

 Spikelets pubescent. 



Plants velvety ; rachis pilose = 8. P. molle. 



Plants glabrous as a whole ; rachis scabrous only. 



9. P. adspersum. 

 Fruit not transversely rugose (minutely papillose-roughened in P. mille- 

 grana). 

 Plants annual. 



Spikelets pubescent, 1.2 to 1.3 mm. long, long-pediceled in an open 



delicate panicle; blades ovate-lanceolate 41. P. trichoides. 



Spikelets glabrous, 2 mm. long or more; blades linear or linear- 

 lanceolate. 

 First glume not over one-fourth the length of the spikelet, truncate 

 or triangular-tipped. (Dichotomifloea in part.) 



Sheaths glabrous 10. P. dichotomifiorum. 



Sheaths papillose-hispid r 11. P. bartowense. 



First glume usually as much as half the length of the spikelet, 

 acute or acuminate. (Capillaeia.) 

 Inflorescence elongate, composed of several approximate implicate 



panicles 16. P. cayennense. 



Inflorescence not composed of approximate nor implicate pan- 

 icles. 

 Panicles more than half the length of the entire plant ; spike- 

 lets 2 to 2.2 mm. long 14. P. capillare. 



Panicles not more than one-third the length of the entire 



plant; spikelets 3 to 3.3 mm. long_. 15. P. hirticaule. 



Plants perennial. 



Spikelets short-pediceled along one side of the panicle branches, 

 forming more or less spikelike racemes. 



Second glume inflated-gibbous, pubescent 45. P. ineptum. 



Second glume not inflated-gibbous. 

 Blades lanceolate or ovate-lanceolate. (Stolonifeba.) 



