17. Annual or biennial; rhizome wanting; stems scarcely thickened or fibrous- 



coated basally; leaf sheaths often reddish-brown or purplish-brown 

 at base; bracts erect or ascending; inflorescence with 2 to 5 rays, 



rarely a single head; achenes brown or purplish-brown 



16. C acuminatus. 



18(15). Achenes only 0.7-0.8 mm. long; culms with scattered microscopic re- 

 trorse projections like shark's teeth 17. C. surinamensis. 



18. Achenes 0.9-1.5 mm. long; culms either smooth or with antrorse or hori- 



zontal projections (19) 



19(18). Culms 5-12 mm. thick basally, apically 3-8 mm. thick and with micro- 

 scopic antrorse projections like shark's teeth; scales 2-2.4 mm. long, 

 when spread out 1.2-1.5 mm. broad at the broadest point (just 

 below the middle) 18. C. virens. 



19. Culms 0.7-5 mm. thick basally, apically 0.4-2.7 mm. thick, either smooth or 



with microscopic knobs (very rarely with antrorse projections in 

 C. pseudovegetus); scales 1.3-1.9 mm. long (20) 



20(19). Scales with the dorsal basal flat portion or groove continuing a third to 

 half the total length of a scale and 0.3-0.5 mm. broad; scales when 

 spread out 1.5-1.9 mm. broad near the base and tapering all the 

 way to the apex; achene 1.3-1.5 mm. long, 0.5-0.6 mm. thick, 

 maturing to a nearly black color 19. C. ochraceus. 



20. Scales with the dorsal basal flat portion or groove continuing only a fifth to 



a third the total length and only 0.1-0.2 (-0.3) mm. broad; scales 

 when spread out 0.6-1.2 mm. broad at the broadest (near the 

 middle or shortly below); achene 0.9-1.3 mm. long, 0.2-0.45 mm. 

 thick, maturing to a brownish color (21) 



21(20). Scales essentially linear for most of the length, only 0.6-0.7 mm. broad 

 and (as folded in place) the whole scale incurved-falcate; achene 

 linear, 0.2-0.3 mm. thick 20. C. pseudovegetus. 



21. Scales ovate, reddish with greenish keels, 0.8-1.1 mm. broad at the broadest 



point, as folded in place the lower part of the keel incurved but 

 the upper part straight , 21. C. reflexus. 



22(12). Most leaves reduced to mere bladeless sheaths or occasionally the upper- 

 most sheaths with short blades very rarely to 10 cm. long (23) 



22. Even the lower leaves with well-developed blades (26) 



23(22). Inflorescence (not including bracts) 1-2 cm. long 22. C. phaeolepis. 



23. Inflorescence (not including bracts) 3-35 cm. long (24) 



24(23). Bracts usually 2, 1 of them 0.3 to 1 (to 2) times as long as the inflores- 

 cence 23. C Haspan. 



24. Bracts 10 to 25, often much-surpassing the inflorescence (25) 



25(24). Internodes of spikelet axes with deciduous wings about 1 mm. long and 

 0.2-0.3 mm. broad 24. C. giganteus. 



25. Spikelet axes wingless : 25. C. alternifoUus. 



26(22). Achene 0.4-0.7 mm. long, 0.4-0.5 mm. thick, subglobose, white; bracts 

 usually only 2 in number 23. C. Haspan. 



26. Achene 0.7-3 mm. long, usually considerably longer than thick; bracts 3 to 



13 (27) 



27(26). Scales 1.3-2 mm. long; achenes 0.8-1 mm. long, 0.3-0.6 mm. thick, 

 unequally trigonous; spikelet axis with readily deciduous wings, 

 0.2-0.3 mm. broad; spikclets only 1 mm. broad, much-compressed, 

 borne 15 to 70 together in spikes (28) 



418 



