58 FLOE A OF PEILADELFEIJ. 



Style 3-cleft; achene 3-angled. 



Scales falling away from the persistent rachis of the flattened spikelet. 

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



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



5. C. inflexus. 

 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. 6. C. compressus. 



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



7. C. pseudovegetus. 

 Wings of the rachis evident. 



Low annual, adventive from Europe ; scales brown. 



8. C. fuscits. 

 Tall indigenous perennials. 



Scales mucronate, reddish-brown or green. 



9. C. dentatus. 

 Scales acute or obtuse, not mucronate. 



Scales wholly or partly purple-brown; achene 



linear. 10. C. rotundus. 



Scales straw-colored ; achene ovoid. 



11. C. escidentus. 

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



12. C. erythrorhisos. 

 Spikelets falling away from the axis of the spikes, the lower pair of 



scales commonly persistent. 

 Annuals ; spikelets elongated, nearly terete. 



Scales imbricated; achene obovoid. 13. C. speciosus. 



Scales distant; achene linear-oblong. 14. C. Engelmanni. 

 Perennial by hard^ tuber-like basal corms; spikelets more or less 

 flattened. 

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

 Spikelets flat, several-many-flowered. 



15. C. strigosus. 

 Spikelets subterete, few-flowered. 



Spikelets 12-25 mm. long, loosely spieate ; lower re- 

 flexed. 16. C. refractus. 

 Spikelets 3-12 mm. long, densely capitate or spieate. 

 Spikelets all reflexed ; culms rough. 



17. C. retrofractus. 

 Spikelets spreading or only the lower reflexed; 

 culms smooth. 

 Heads oblong or cylindric. 



Spikelets 6-10 mm. long, the lower re- 

 flexed. 18. C. Lancastriensis. 

 Spikelets 3-4 mm. long, the lower spread- 

 ing. 19. C. cyJindricus. 

 Heads globose. 20. C. ovxdaris. 

 Achene oblong or obovoid, about twice as long as thick. 

 Eaehis wingless or very narrowly winged. 



21. C. fiUculmis. 

 Eachis-wings membranous, broad. 



Scales firm, not appressed, spikelet loosely capitate. 



22. C. Grayi. 

 Scales thin, closely appressed ; spikelets densely cap- 

 itate. 23. C. echinatus. 



1. Ctperus flavescens L. M. p. 161. Low grounds. Summer. 



PMtodeZpMa— Byberry, Mart. (B. C), on the Delaware Eiver (P.). 

 Buchs—'NeSiT Bristol, Mart. (Fr.). Delaware— Wavfa (P.), Valley of 

 Darby Creek (B. Sm.). Lancaster— {!?.). Northampton— 'Eastou. (P.). 

 Dauphin — (P.). 



