320 American Midland Naturalist Monograph No. 7 



5. Beak of the perigynium serrulate; achenes longer than 



wide, the angles not thickened; swamps, common 



C. lupulina Muhl. 



5. Beak of the perigynium smooth; achenes as wide as long, 

 the angles prominently thickened; wet ground, local 

 C. lupuliformis Sartw. 



2. Mature perigynia not more than 1 cm long. 



6. Leaves involute-filiform; pistillate spikes 1 or 2, sessile, glo- 

 bose, few-flowered; perigynia ovoid, turgid, glossy, 4-7 

 mm long, nearly twice the length of the obtuse glumes; 

 bogs; Lake Co., Hill in 1908 C. oligosperma Michx. 



6. Leaves flat. 



7. Perigynia obovoid, 4-5 mm long, truncate above and 

 abruptly subulate-beaked; terminal spike often mostly 

 pistillate. 



8. Perigynia shorter than the serrulate, linear-subulate 

 glumes; ditches and swamps; northward to McLean 

 and Adams counties C. frankii Kunth 



8. Perigynia much longer than the glumes. 



9. Perigynia squarrose; glumes acute to mucronate; style 

 strongly curved near the ovary; swampy ground and 

 roadside ditches, common C. squarrosa L. 



9. Perigynia ascending; glumes obtusish or acutish; style 

 straight throughout; swamps and roadside ditches; 

 chiefly in the southern half of 111., extending north- 

 ward to Macon Co. [C. typhinoides Schw.] 



C. typhina Michx. 



7. Perigynia lanceoloid, ellipsoid, or ovoid. 

 10. Glumes with a serrulate awn. 



11. Perigynia lanceoloid, strongly ribbed, soon reflexed, 

 5-7 mir long, the beak equalling or exceeding the 

 body; teeth strongly divergent, 1-2 mm long; 

 swamps and ditches, local. [C pseudocyperus of 



auth.] C. comosa Boott 



11. Perigynia ellipsoid or ovoid, often inflated, 5-9 mm 

 long. 

 12. Perigynia 15- to 20-nerved, 1.5-2 mm thick, the 

 beak 2 mm long; wet ground, common; chief- 

 ly in the northern half of the state 



C. hystricina Muhl. 



12. Peiigynia 8- to 10-nerved, 2.5-3 mm thick, the 

 beak 3-4 mm long; swamps, wet meadows, 



and ditches, common C. lurida Wahl. 



10. Glumes not serrulate. 



13. Beak of the perigynium 0.5-1 mm long, minutely 

 bidentate. 



