FLOWERING PLANTS AND FERNS OF ARIZONA 157 



Achene triangular; style branches 3, or sometimes only 2, in C. seslerioides (4). 



4. Rachilla of the spikelet with numerous articulations, one below each scale, 



the joints separating readily at maturity; stems usually tall and stout; 



inflorescence typically large, compound, with some of the rays elongate; 



spikelets very slender, mostly 8 mm. long or longer, pale yellowish brown 



to reddish brown when mature 21. C. ferax. 



4. Rachilla not articulated or with only one articulation just above the base, 

 the joints not separating (5). 

 5. Scales cuspidate to aristate, the tips spreading in age (6). 



6. Plant stoloniferous; stamens 3; stems seldom less than 30 cm. long; 



scales strongly several-nerved (7). 



7. Scales broadly ovate, merely cuspidate, the spikes not appearing 



bristly; central spike oblong or ovoid-oblong, usually much longer 



than the lateral ones, all sessile or nearly so; stolons thick and 



hard, tuberlike, mostly not more than 1 cm. long. 



13. C FENDLERIANUS. 



7. Scales ovate-lanceolate, long-aristate, giving the spikes a bristly 



appearance; spikes all broadly ovoid or globose, some of them 

 on more or less elongate, slender rays; stolons slender, thickened 

 at the distal end, mostly 2 cm. long or longer. 



15. C. WRIGHTII. 

 6. Plant not stoloniferous; stamen normally only 1 (8). 



8. Spikelets very slender, usually less than 2 mm. wide, more than 3 



times as long as wide, spreading, in umbellike clusters, these either 

 sessile or borne on slender rays; scales merely cuspidate, bright 



reddish brown; plant annual 6. C. amabilis. 



8. Spikelets more than 2 mm. wide, not more than 3 times as long as 

 wide (9). 

 9. Scales 5- to 9-nerved, with reddish or brownish margins, ending in 

 a slender, wide-spreading or recurved awn more than one- 

 third as long as the body of the scale; plant annual, strong 



scented when dry 17. C. aristatus. 



9. Scales 3-nerved, pale green when fresh, becoming yellowish brown, 

 with broad, white or only slightly colored margins, ending in a 

 stout, moderately spreading cusp much less than one-third as 

 long as the body of the scale (10). 

 10. Plant annual; bracts of the involucre suberect; inflorescence 

 usually with one or more slender rays; achene narrow, acumi- 

 nate, light-colored 4. C. acuminatus. 



10. Plant perennial; bracts more or less reflexed; inflorescence con- 

 tracted, subcapitate; achene broad, obtuse and often abrupt- 

 ly apiculate, becoming nearly black; stems bulbous-thickened 



at base 7. C. seslerioides. 



5. Scales muticous or mucronate, the tips not or but slightly spreading (11). 

 11. Plant stoloniferous, the stolons longer than thick (12). 



12. Scales loosely imbricate, wider than long, greenish or olive brown, 



prominently several-nerved; plants of relatively dry situations 



(13). 



13. Stolons mostly more than 1 cm. long, slender at the proximal end, 



thickened at the distal end; inflorescence usually contracted, the 



spikes dense, most of them sessile or nearly so; stems and leaves 



often scabrous or hispid 12. C. manimae. 



13. Stolons mostly less than 1 cm. long, uniformly thick, hard, tuber- 



like; inflorescence open, the spikes usually loose, some of them 

 borne on long, slender rays; stems and leaves smooth. 



14. C. RUSBYI. 

 12. Scales closely imbricate, longer than wide, golden brown or ma- 

 hogany-colored; stolons elongate, slender most of their length 

 but often tuberous-thickened toward the distal end; plants of 

 marshes, stream beds, and irrigated fields (14). 



14. Scales mahogany-colored, the lateral nerves inconspicuous; rachis 



of the spike usually shorter than the spikelets. 



2. ('. ROTUNDUS. 



14. Scales golden brown (exceptionally reddish brown) the Lateral 

 nerves conspicuous; rachis usually as long as or longer than 

 the spikelets 3. C. esculextus. 



