27. Scales (at least the fertile ones) 2.3-5.5 mm. long; spikelet axis either wing- 



less or with more or less persistent wings; spikelets variously borne 

 but if only 1 mm. broad then not much-compressed (29) 



28(27). Internodes of spikes to 0.5 mm. long; scales 1.3-1.5 mm. long 



26. C erythrorhizos. 



28. Internodes of spikes 0.6-2 mm. long; scales 1.5-2 mm. long.. 27. C. digitatus. 



29(27). Achene 0.25-0.3 mm. thick 28. C. onerosus. 



29. Achene 0.4-1.2 mm thick (30) 



30(29). Achene 1-1.3 mm. long (31) 



30. Achene 1.3-3 mm. long, much longer than thick (32) 



31(30). Achene 1-1.3 mm. long, nearly as thick as long, pale or brown; spikelets 

 much-compressed; scales 3-3.5 mm. long, acuminate, the keel 



grayish-white, the broad margins pale and hyaline 



29. C. compressus. 



31. Achene 1-1.2 mm. long, about half as thick, nearly black; scales 2-3 mm. 



long, obtuse, the keel green, the sides reddish-brown 



30. C. Parishii. 



32(30). Spikelet axis internodes essentially wingless, occasionally with wings to 

 0.2 mm. broad (33) 



32. Spikelet axis internodes with wings 0.3-1.2 mm. broad (35) 



33(32). Nonviscid perennial, tufted and usually with extensive knotty subrhizo- 

 matous bases; secondary peduncles absent; leaves neither spongy 

 nor septate basally; inflorescence a single dense sessile head 1-3 

 cm. thick with 15 to 55 spikelets 31. C filiculmis. 



33. Viscid tufted perennials with culms 3-7 mm. thick, the longer peduncles in 



most inflorescences with secondary peduncles each bearing a head 

 similar to those of the shorter primary peduncles; leaves spongy at 

 base, when dried their incomplete septa visible, the leaf apexes 

 involute (34) 



34(33). Spikelets grayish-ochraceous turning grayish-brown; achene thickest 

 (0.7-0.8 mm.) near the apex, long-tapered to the base, 1.4-1.8 

 mm. long, only slightly apiculate 32. C. elegans. 



34. Spikelets grayish-yellow becoming rich-golden-brown; achene nearly cylin- 



drical or very slightly thickened in the upper part, long-tapered 

 below, the main part 1.5 mm. long and 0.5 mm. thick but also with 

 the persistent style base (or very large apiculus) adding almost 

 1 mm. to the length 33. C. oxylepis. 



35(32). Rhizomatous perennials; spikelets with 6 to 40 eventually deciduous 

 scales; spikelet axes persistent on the axis of the cluster or spike (36) 



35. Tufted perennials (occasionally with knotty subrhizomatous bases in C. 



huarmensis) ; spikelets with 2 to 8 scales (up to 20 in C. strigosus) 

 and these persistent (deciduous in some specimens of C. strigosus) ; 

 spikelet axis deciduous (more or less so in C. strigosus) (38) 



36(35). Bracts 3 or 4, about equaling the inflorescence; inflorescence with 20 to 

 65 spikelets altogether, usually even the longer primary peduncles 

 bearing a simple cluster or spike of spikelets just as do the shorter 

 peduncles; each cluster or spike with 3 to 9 spikelets; wings of 



spikelet axis 2-3 mm. long; achenes 0.9-1 mm. thick 



34. C rotundus. 



36. Bracts 5 to 13, usually much-surpassing the inflorescence; inflorescence with 



70 to 350 spikelets altogether; the longer primary peduncles usually 

 with several nearly sessile clusters or spikes of spikelets; each cluster 

 or spike with 10 to 50 spikelets; wings of spikelet axis 1-1.5 mm. 

 long; achenes 0.4-0.8 mm. thick (37) 



419 



