160 FLORA. 



commonly sessile. Spikelets flat or subterete, the scales falling away from the 

 rachis as they mature (nos. [-19), or persistent and the spikelets falling away from 

 the axis of the head or spike with the scales attached (nos. 20-32). Scales con- 

 cave, conduplicate or keeled, 2 -ranked, all flower-bearing or the lower ones empty. 

 Flowers perfect Perianth none. Stamens 1-3. Style 2-3-cleft, deciduous from 

 tin.' Mimniit of the achene. [Ancient Greek name for these sedges.] About 650 

 species, of with- distribution in tropical and temperate regions. Besides the fol- 

 lowing, some 40 others occur in the southern U. S. 



Style 2-cleft ; achene lenticular, not 3-angled ; scales falling ."rom the rachis ; spikelets 

 flat. 

 Achene one-half as long as the scale ; umbel nearly or quite simple. 



Spikelets yellow ; superficial cells of the achene oblong. 1. C. flavescens. 

 Spikelets green or brown ; superficial cells of the achene quadrate. 

 Scales obtuse or obtusish, appressed. 



Scales membranous, dull ; style much exserted. 2. C. diandrus. 

 Scales subcoriaceous, shining ; style scarcely exserted. 



3. C. rivularis. 

 Scales acute, somewhat spreading at maturity. 



Achene narrowly obovate ; spikelets 1-3 cm. long. 4. C. Nuttallii. 

 Achene linear-oblong ; spikelets 0.5-2 cm. long. 5. C. microdontus. 

 Achene nearly as long as the scale ; umbel sometimes much compound. 



6. C. Jlavicomus. 

 Style 3-cleft ; achene 3-angled. 



A. Scales falling away from the persistent rachis of the flattened spikelets. 

 Wings of the rachis, if present, permanently adnate to it. 



Scales tipped with recurved awns ; low annual, 2-15 cm. tall. 



7. C. injlexus. 

 Scales acute or obtuse, not awned. 



Wings of the rachis none or very narrow. 



Stamens 3 ; spikelets linear-oblong, 8-25 mm. long ; scales acute, 

 Annual ; culms smooth, 5-25 cm. long. 8. C. compressus. 

 Perennial ; culms rough, 30-85 cm. tall. 9. C. Schweinitzit. 

 Stamen 1 ; spikelets ovate, 4-8 mm. long. 



Tall perennial ; achene linear ; scales acutish. 



10. C. pseudovegetus 

 Low annual ; achene oblong ; scale-tips recurved. 



11. C. acuminatus. 

 Wings of the rachis evident. 



Low annual, adventive from Europe ; scales brown. 



12. C. fuscus. 

 Tall indigenous perennials (no 13 sometimes annual ?). 



Lower leaves reduced to pointed sheaths. 



13. C. Haspan, 

 Leaves all elongated-linear. 



Scales mucronate, reddish brown or green. 



14. C. dentatus. 

 Scales acute or obtuse, not mucronate. 



Scales wholly or partly purple-brown ; achene linear. 

 Scales tightly appressed. 15. C. rotundus. 

 Tips of the scales free. 16. C. Hallii. 



Scales straw-colored ; achene obovoid. 



17. C. esculentus. 

 Wings of the rachis separating from it as interior scales ; annuals. 



Spikes loose ; spikelets 6 20 mm. long. 18. C. erythrorkizos. 



Spikes dense, cylindric ; spikelets 3-5 mm. long. 19. C. Halei. 



B. Spikelets falling away from the axis of the spikes, the lower pair of scales com 

 monly persistent. 



Annuals ; spikelets elongated, nearly terete. 

 Scales imbricated; achene obovoid. 



Scales thin, dull brown; spikelets very slender. 20. C. speciosus. 

 Scales rigid, yellow-brown ; spikelets stout. 21. C. ferax. 



Scales distant, achene linear-obloijg. 22. C. Englemanni, 



Perennial by hard, tuber-like basal conns; spikelets more or less flattened. 

 Achene narrowly linear-oblong, 3-4 times as long as thick. 



Spikelets flat, several-many-flowered. 23. C. strigosus. 



Spikelets subterete, few-flowered. 



Spikelets 12-25 mm. I"iig, loosely spicate ; lower reflexed. 



24.. C. re/ractus. 



