7. The edges of the internodal niches essentially wingless (8) 



8(7). Achenial surface with rectangular-linear cells oriented vertically in hori- 

 zontal rows, these rows marked off by horizontal wavy usually dis- 

 colored sutures 7. C. flavescens. 



8. Achenial surface with vertical rows of minute essentially isodiametric usually 



somewhat hexagonal cells; spikelets 7-12 mm. long; scales about 

 2 mm. long 8. C. niger. 



9(1). The spikelet axis at maturity disarticulating at the base of each internode 

 (just above each node), thus breaking into units consisting of a 

 scale, the next lowest internode and the attached wings and clasped 

 achene; internodes postanthetically on the sterile side becoming 



thickened and assuming a white cartilaginous texture 



9. C. odoratus. 



9. The spikelet axis either persistent as a unit or else deciduous as a unit, not 



disarticulating spontaneously at maturity (10) 



10(9). Culms stiffly erect with complete septa at intervals of 5-50 mm 



10. C. articulatus 



10. Culms non-septate (11) 



11(10). Each of the 5 to 8 extremely unequal primary peduncles with an irregu- 

 lar panicle of several spikes each with a number of ascending spike- 

 lets; the total inflorescence with 100 to 600 spikelets; scales when 

 spread out nearly orbicular, about 1.5 mm. long; spikelet axes 

 wingless 11. C Ida. 



11. Each primary peduncle either reduced or bearing a head or spike or a 



glomerule, or bearing several short secondary peduncles but never 

 an irregular panicle; scales usually considerably longer than broad 

 or if nearly as long as broad then longer than 1.5 mm. (12) 



12(1 1). Stamens 1 or 2; spikelet axis wingless or essentially so (13) 



12. Stamens 3; spikelet axis winged or wingless (22) 



13(12). Scales less than 1 mm. long, rounded or truncate at apex, the lateral 



nerves indistinct, hyaline-margined, 3-nerved, caducous, annual 



12. C. difformis. 



13. Scales 1 mm. or longer, acuminate at apex, the lateral nerves prominent (14) 



14(13). Scales with 7 to 9 strong evenly distributed nerves and a wholly keel-like 

 median portion, terminating in a spreading recurved awn; annual, 

 reddish-brown at base 13. C. aristatus. 



14. Scales with 3 or 5 nerves and these sometimes obscure and concentrated in 



the median portion, the tip mostly either incurved or straight (15) 



15(14). Scales 3-nerved, acuminate to cuspidate or aristate (16) 



15. Scales 5-nerved, (3-nerved if culm has retrorse projections) apex blunt, 



rounded or acute (18) 



16(15). Bracts 3 to 6, scarcely if at all surpassing the inflorescence; rays up to 

 10; spikelets to 18 mm. long, reddish-brown, digitate-radiate; scales 

 aristate 14. C. amabilis var. macrostachyos. 



16. Bracts 2 to 4, much-surpassing the inflorescence; rays up to 5; spikelets not 



more than 10 mm. long, in dense heads, white to pale-brown; scales 

 mucronate to acuminate (17) 



17(16). Matted perennial with a tuberiferous rhizome, to 3 cm. long; culm much- 

 thickened and fibrous-coated at the base; leaf sheaths nearly black; 

 bracts more or less reflexed; inflorescence contracted into a single 

 head; achene nearly black 15. C seslerioides. 



417 



