FLORA OF THE DISTRICT OF COLUMBIA. 101 



A«henes trigonous; stigmas 3. 

 Perigynia beakless or, if beaked, without rigid teeth. 



Lower bracts of the inflorescence without conspicuous green sheaths. 

 Spikes solitary, terminal. 



Perigynia beakless; scales short, hyaline 10. Polytrichoideae. 



Perigynia long-beaked; scales long, bractlike 11. Phyllostachyae. 



Spikes 2 or more. 

 Terminal spike entirely staminate. 

 Perigynia pubescent. 

 Leaves and culms glabrous. 



Culms leafy (C. vestita) ' 24. Hirtae. 



Culms not leafy 12. Montanae. 



Leaves and culms pubescent 13. Pubescentes. 



Perigynia glabrous. 

 Spikes stout, sessile or short-peduncled; perigynia nerved. 



14. Pallescentes. 

 Spikes slender, drooping on slender peduncles; perigynia nerveless (C. 



prasina) 18. Gracillimae. 



Terminal spike partly pistillate. 

 Perigynia nerveless except on the margins. 



Spikes drooping; perigjoiia ascending (C prasina) 18. Gracillimae. 



Spikes erect; perigynia refiexed 15. Shortlanae. 



Perigynia nerved 16. Virescen tes. 



Lower bracts of the inflorescence with conspicuous green sheaths. 

 Perigynia nerveless or with few nerves thicker at the base. 

 Spikes slender, drooping. 



Perigynia long-beaked 17- Debiles. 



Perigynia short-beaked 18. Gracillimae. 



Spikes stouter, ascending 19. Paniceae. 



Perigynia with many uniform nerves. 



Nerves impressed 20. Griseae. 



Nerves elevated. 



Perigynia trigonous in cross section 21 . Laxiflorae. 



Perigynia circular in cross section. 



Spikes slender, drooping (C. oblita) 17. Debiles. 



Spikes stouter, ascending or divaricate 22. Granulares. 



Perigynia rigidly bidentate, the teeth sharp. 

 Achenes closely enveloped by the usually firm and tough perigynia. 

 Nerves of the perigynia few or none. 



Perigynia refiexed 23. Flavae. 



Perigynia ascending 24. Hirtae. 



Nerves of the perigynia numerous (15-30) 25. Pseudocyperae. 



Achenes loosely enveloped by the thin papery perigynia 26. Pliysocarpae. 



1. Muhlenbergianae Tuckerm. 



Infiorescence comparatively short, usually green when mature. 



Spikes loosely flowered, delicate; perigynia spongy below the middle. 



Spikes approximate or nearly so; beak of perigynium smooth; scales acuminate. 



1. C. retroflexa. 

 Spikes mostly remote; beak of perigynium minutely roughened; scales blunt. 

 Perigynium broadly lanceolate, sharply contracted into the flat beak; stigmas 



dark brown, thick, twisted 2. C. convoluta. 



Perigynium narrowly lanceolate, slightly contracted into the nearly terete beak; 

 stigmas light brown, slender, straight 3. C. rosea. 



