84 American Midland Naturalist Monograph No. 2 



13. Perigynia 15-20-nerve(d, 1.5-2 mm. thick, the beak 2 mm. 

 long; wet ground, common; chiefly in the n. half of the 

 state C. hystricina Muhl. 



13. Perigynia 8-10-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. 



14. Beak of the perigynium 0.5-1 mm. long, minutely bidentate; 

 perigynia ellipsoid, 2-3.5 mm. long; lake shores and river 

 banks, n.e. 111. [C. oedert var. pumda (Coss. & Germ.) 

 Fern.] C. viridula Michx. 



14. Beak of the perigynium 2-2.5 mm. long, equalling or exceed- 

 ing the body. 

 15. Pistillate spikes erect, sessile; perigynia spreading or re- 

 flexed, 2-3 times as long as the glumes; beak of the 



perigynium sparsely serrulate; wet meadows, n.e. Ill 



C. viridula Michx. 



15. Pistillate spikes pendulous on slender peduncles; perigynia 

 spreading-ascending, about as long as the glumes; beak 

 smooth; alluvial soil in the n. half of the state. [C. 



longirostris sensu Torr., non Krock} 



C. sprengeln Dewey 



1. Staminate spikes two or more; perigynia ovoid or ovoid-lanceoloid, usually 

 more or less inflated. 

 16. Teeth of the perigynium short, not more than 0.5 mm. long. 



17. Perigynia fusiform or narrowly ellipsoid, short-beaked, the beak not 

 more than 1 mm. long. 



18. Perigynia strongly nerved; swamps and ditches 



C. lacustris Willd. 



18. Perigynia impressed-nerved; ditches, and wet ground in woods... 

 C. hyaltnolepis Steud. 



17. Perigynia ovoid-lanceoloid, inflated, papery, strongly nerved; beak 



2-3.5 mm. long; swampy ground, local C. retrorsa Schw. 



16. Teeth of the perigynium 0.5-2 mm. long. 



19. Perigynium 5-6.5 mm. wide, 7-10 mm. long, the teeth 0.5-1 mm. 

 long; wet ground in woods; Lake Forest, Vasey; Cook Co., Gates 

 C. tucker mam Dewey 



19. Perigynium 2-3.5 mm. wide. 



20. Teeth 1-2 mm. long; marshy ground C. laevicotiica Dewey 



20. Teeth 0.5-1 mm. long. 



21. Lower perigynia refle.xed or widely spreading; stems scattered, 

 obtusely angled; plants stoloniferous; leaves 4-12 mm. wide; 



ditches and shores, n. Ill C. rostrata Stokes 



21. Perigynia ascending; stems cespitose, sharply angled; leaves 

 3-5 mm. wide; swamps, and wet ground in woods, chiefly in 

 the n. half of the state C vesicaria L. 



