145. Ca-feracear 307 



3. Bract 1-5 cm long, twice the length of the cylindrical or ovoid 

 spikelet; shallow water, Wolf Lake, Chicago, Cook Co., 

 July 26, 1890, E. J. Hill: swamp, Waukegan, Lake Co., 

 R. A. Harper in 1891 S. suhtcrminalis Torr. 



3. Bract shorter than or equalling the spikelet; Ringwood, Mc- 



Henry Co., Vasey S. cespitosus L. 



2. Spikelets usually more than one. 



4. Spikelets few, appearing lateral. 



5. Stems terete, or obtusely 3-angled; plants annual, tufted; 



bristles minute or absent, or equalling or exceeding the 



achene. 



6. Spikelets solitary or rarely 2, the glumes boat-shaped, 



keeled, stronglv convex: stems filiform, 0.2-0.3 mm 



thick; low wet ground, rare; Alexander Co., H. E. 



Allies in 1951. [.S". carinatus (H. & A.) A.Gray, not 



Sm.] S. koilolepis (Steud.) Gleason 



6. Spikelets more than one, usually several; glumes flat or 

 nearly so; stems 0.7-2 mm thick. 

 7. Achenes strongly transversely rugose; low sandy places 



in Cass, Mason, and Menard counties 



S. hallii A.Gray 



7. Achenes obscurely ridged, or smooth. 



8. Stems subterete with rounded sides; spikelets acut- 

 ish; involucral bract always erect; achenes glossy, 



black, plano-convex; wet shores, rare 



S. smithii A.Gray 



8. Stems obtusely 3-angled with concave sides; spike- 

 lets blunt; involucral bract usually divaricate at 

 maturity; achenes dull, unequally biconvex, or 

 lenticular; wet soil, rare; Hancock, Lawrence, 

 and Mason counties. [S. debilis of auth., not 



Lam.] S. purshianus Feni. 



5. Stems sharply 3-angled; plants perennial, with rhizomes. 

 9. Bristles longer than the trigonal achenes; glumes yellow- 

 ish-brown, entire, mucronate; St. Clair Co., G. Engel- 



mann S. torreyi Olney 



9. Bristles not longer than the plano-convex achenes; 

 glumes reddish-brown, awn-tipped; shores and marshy 



ground throughout 111. Three-square 



S. americanus Pers. 



4. Spikelets in compound umbels. 



10. Achenes trigonal, 2.5 mm long; spikelets ovoid to cylindri- 

 cal, 7-15 mm long, usually solitary on the slender 

 branches; shallow water, rare; known in 111. from Hen- 

 derson, Menard, and St. Clair counties 



S. heterochaetus Chase 



10. Achenes biconvex; spikelets 2-several on the slender 

 branches. 



