22 POALES 



Leaves glabrous, several of the upper spikelets staminate. 



8. C. riparia. 

 Perigynia pubescent. 



Pistillate spikes large, 1-2.5 cm. long. 



Leaves flat, 2-5 mm. wide. 9. C. lanuginosa. 



Leaves involute, about 1 mm. wide. 10. C. filiform is. 



Pistillate spikes small, usually less than 1 cm. long. 

 Staminate spike large, 1-2.5 cm. long. 



27. C. pennsylvanica. 

 Staminate spike small, 4-8 mm. long. 28. C. varia. 



Perigynia with entire beaks or beakless. 

 Perigynia 4-5 mm. long. 



Pistillate spikes dense, many flowered, 18. C. grisea. 



Pistillate spike loose, few flowered. 19. C. amphibola. 



Perigynia usually not over 3 cm. long. 

 Spikes two or more, the upper staminate. 



Pistillate spikes densely flowered or drooping. 



Pistillate spikes drooping. 15. C. limosa. 



Pistillate spikes not drooping. 



Bracts with long blades, much exceeding the subtended 

 spikes. 

 Bracts mostly overtopping the spikes, perigynium 

 strongly many nerved. 20. C. granularis. 



Bracts rarely overtopping the spikes, perigynium ob- 

 scurely few nerved. 21. C. crawel. 

 Bracts short, rarely over twice the length of the sub- 

 tended spikes. 

 Perigynia about 3 mm. long. 23. C. meadil. 

 Perigynia about 2 mm. long. 11. C. buxbaumit. 

 Pistillate spikes loosely few flowered. 



Pistillate spikes not globose, usually over 1 cm. long. 

 Tip of perigynia bent outward. 24. C. laxlflora. 



Tip of perigynia straight or nearly so. 



Perigynia 3-4 mm. long. 22. C. oligocarpa. 



Perigynia 2 mm. long. 25. C. aurea. 



Pistillate spikes globose, 4-8 mm. long, 26. C. setifolia. 

 Spikes solitary. 



Spikes not overtopped by bracts 30. C. fllifolla. 



Spikes overtopped by leafy bracts. 29. C. durifolia. 



Achenes lenticular, stigmas two. 



Spikes unlike, the upper mostly or entirely staminate, the lower 

 mostly pistillate. 

 Pistillate spikes densely flowered. 



Orifice of perigynia entire or nearly so. 

 Lower sheaths prominently fibrilose, scales equal to perigynia 

 in length. 12. C. stricta. 



Lower sheaths less fibrilose, scales longer than perigynia. 



13. C. haydenl. 



Orifice of perigynia with 2 teeth, 14. C. nebraskensis. 



Pistillate spike few flowered, 25. C. aurea. 



Spikes alike or nearly so, all with both staminate and pistillate 



flowers. 



