216 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Blades with a white-carti- 

 laginous margin, not cili- 

 ate; spikelets 1.5 mm. 



long 44. P. tenue. 



Blades without white mar- 

 gin, ciliate toward the 

 cordate base; spikelets 

 scarcely over 1 mm . long, 



suborbicular 13. P. erectifolium. 



Plants not forming winter rosettes. 



Panicles narrow and compact with appressed branches; 

 spikelets glabrous, 1 to 2.5 mm. long. 



Culms 1 meter or more tall, compressed at base; pan- 

 icle 10 to 20 cm. long; spikelets 2.5 mm. long 9. P. condensum. 



Culms 60 cm. or less tall, stiff and wiry, base not com- 

 pressed; panicle less than 5 cm. long; spikelets 1 to 

 2 mm. long. 



Spikelets scarcely more than 1 mm. long 40. P. stenodes. 



Spikelets 2 mm. long 43. P. tenerum. 



Panicles open, usually diffusely spreading. 



Panicle branches in several distinct distant whorls; 

 spikelets short -pediceled, remote along the 



branches 26. P. megiston. 



Panicle branches not in distinct whorls. 



Spikelets 5 to 6 mm. long, pedicels short and 



stout; panicle branches few, ascending 49. P. zizanioides. 



Spikelets less than 5 mm. long, pedicels slen- 

 der, often capillary. 

 Plants producing scaly rootstocks. 



Blades 5 to 15 cm. long; culms less 



than 50 cm. tall; a sea-shore grass 34. P. repens. 



Blades elongated, 20 to 40 cm. long; 



culms 1 meter or more tall 47. P. virgatum cubense. 



Plants not producing rootstocks, but culms 

 sometimes decumbent and rooting at base. 



Spikelets glutinous, 3 mm. long 18. P. glutinosum. 



Spikelets not glutinous. (See contin- 

 uation 2.) 

 (Continuation 2.) 

 Spikelets warty-rugose, about 2 mm. long; blades ovate- 

 lanceolate 38. P. sellovii. 



Spikelets not rugose. 



Spikelets pubescent, minute (1 mm. long); blades ovate- 

 lanceolate 46. /'. trichoides. 



Spikelets glabrous. 



Spikelets 1.5 mm. loim, short-pediceled on the spread- 

 ing branches of a panicle 2 to 5 cm. long: culms 

 slender, 30 to 50 cm. high, blades 1 to 2 mm. wide. 14. P. exigwiflorum. 

 Spikelets on more or less elongated pedicel.-. 



Culms Blender, widely decumbent -spreading; 

 blades elliptic-lanceolate, 1 to 3 cm. long, 

 glaucous 30. P. parvifoiium. 



