FLORA OF THE DISTRICT OF COLUMBIA. 105 



14. Pallescentes Fries. 



Plant glabrous; staminate spike terminal; pistillate spikes short and stout; perigy- 

 nia ascending. 



A single species 49. C. pallescens. 



15. Shortianae Bailey. 



Spikes brown, evenly cylindric, the tips of the densely crowded perigynia re- 

 curved and without teeth. 



A single species 50. 0. shortiana. 



16. Virescentes Kunth. 



Leaves long and slender, the sheaths, at least, hairy; terminal spike staminate 

 below; lower bracts of the inflorescence without conspicuous green sheaths. 



Perigynia densely pubescent. 

 Terminal spike 9-18 mm. long; leaves usually exceeding the culms. . .51. C. swanii. 

 Terminal spike 18-40 mm. long; leaves usually shorter than the culms. 



52. 0. virescens. 

 Perigynia glabrous (at least at maturity). 



Leaves (except sheaths) glabrous 53. C. caroliniana. 



Leaves pubescent. 



Scales acute to short-cuspidate, shorter than the perigynia; staminate portion 



of terminal spike short 54. C. complanata. 



Scales rough-cuspidate, usually much longer titan the perigynia; staminate por- 

 tion longer 55. C. bushii. 



17. Debiles Carey. 



Habit very lax; base of the lowest bract of the inflorescence long-sheathing; spikes 

 slender, drooping; perigynia thin-toothed, more or less long-beaked. 



Perigynia lightly nerved or nerveless; upper sheaths glabrous 56. C. debilis. 



Perigynia strongly nerved; upper sheaths puberulent 57. C. oblita. 



18. Gracillimae Carey. 



PerigjTiia short-beaked, few-nerved, in long drooping spikes; lowest bracts of the 

 inflorescence sheathing. 



Leaves glabrous; perigynia less than 2 mm. thick. 



Lower bracts of the inflorescence long-sheathing 58. 0. gracillima. 



Lower bracts short-sheathing 59. C. prasina. 



Leaves pubescent; perigynia more than 3 mm. long 60. C. davisii. 



19. Paniceae Tuckerm. 



Plant with long slender rootstocks and rather laxly flowered pistillate spikes of 

 strongly few-nerved perigynia. 



A single species 61. C. tetanica. 



20. Griseae Bailey. 



Distinguished from all other species in our region by the impressed nerves of the 

 perigynia. 



Perigynia tapering at the base, constricted at the apex, obtusely triangular in cross 

 section. 



Sheaths glabrous; perigynia 4.5-5 mm. long 62. C. oligocarpa. 



Sheaths pubescent; perigynia 3.5-4 mm. long 63. C. hitchcockiana. 



