308 American Midland Naturalist Monograph No. 7 



ll.Achenes 2 mm long; glumes 2-2.5 mm long, nearly 

 glabrous, slightly spotted; inflorescence lax; spike- 

 lets ovoid, 5-10 mm long; stems soft, easily com- 

 pressed; marshes and shallow water, throughout 

 111 S. validus Vahl 



11, Achenes 2.5 mm long; glumes 3-4 mm long, more or 

 less viscid-puberulent, brown-spotted; inflorescence 

 condensed; spikelets ellipsoid, 1-2 cm long; stems 

 firm and hard; shallow water, local. [S. occidentalis 

 (Wats.) Chase] S. acutus Muhl. 



1. Involucral bracts several, loliaceous; stem more or less 3-angled, 

 leafy; plants perennial. 



12. Spikelets 1-4 cm long; achenes 2.5-4 mm long. 



13. Achenes strongly 3-angled, 4-5 mm long; bristles 6, well- 

 developed; wet ground, local 



S. fluviatilis (Torr.) A.Gray 



13. Achenes more or less compressed or obtusely 3-angied, 3- 



4.5 mm long; bristles 2-6, usually weakly-developed; wet 



ground, rare. Cook Co.; adv. from w. U.S 



S. paludosus A.Nels. 



12. Spikelets numerous, 3-8 mm long, umbellate or paniculate; 

 achenes about 1 mm long. 



14. Spikelets in dense glomerules in stiff-rayed decompound 



umbels; bristles retrorsely minutely barbed, at least at 



apex, rarely absent. 



15. Spikelets 2.5-3 mm long, commonly proliferous; leaves 



4-6 mm wide; bristles much longer than the achene, 



flexuous; wet groimd in woods in the southern half 



of the state S. polyphyllus Vahl 



15. Spikelets 3-9 mm long; leaves 6-16 mm wide; bristles 



straight, or none. 



16. Style usually 3-cleft; bristles about equalling the 



achene or shorter, or absent, barbed only above 



the middle; along ditches, streams, lake shores, 



or in wet woods throughout 111. [S. gcorgianus 



Harper] S. atrovircns Willd. 



16. Style usually 2-cleft; bristles usually 4, barbed near- 

 ly to the base, equalling or slightly exceeding 

 the achene; lower sheaths red-banded; swamps, 



rare; Lake Co., F. C. Gates 2270, 3059 



- S. rubr otitic tus Fern. 



14. Spikelets in loose clusters in larger drooping panicles; 

 bristles smooth, flexuous, much longer than the achene. 

 17. Spikelets cylindrical, 5-8 mm long; leaves 4-7 mm 

 wide; bristles not exceeding the glumes; wet ground 



in woods, or along ditches, common 



S. lineatus Michx. 



