Jones: Flora of Illinois, 23. Cyperaceae 73 



9. SciRPUS L — Bulrush 



1. Involucral bract one, appearing like a continuation of the stem, or lacking. 

 2. Spikelets soUtary, rarely two. 



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



in ponds and slow streams, or on muddy shores, rare. Cook Co 



S. subterminalis Torr. 



3. Bract shorter than or equalling the spikelet; bogs, n. 111. Ringwood, Mc- 



Henry Co., Vasey S. cespitosus L. 



2. Spikelets usually several to many. 



4. Spikelets few, 1-12, appearing lateral. 



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



minute or absent, or equalling or exceeding the achene. 



6. Stems subterete with rounded sides; spikelets acutish; involucral 



bract always erect; achenes glossy, black, plano-convex; wet 



shores, rare ^S". smithit Gray 



6. Stems obtusely 3-angled with concave sides; spikelets blunt; invol- 



ucral bract usually divaricate at maturity; achenes dull, un- 

 equally biconvex, or lenticular; wet soil, rare. Mason Co., Vasey 



in 1862. [S. debilis of Pursh, not Lam.] S. purshianus Fern. 



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



7. Bristles longer than the trigonal achenes; glumes yellowish brown, 



entire, mucronate; swamps ..S. torreyl Olney 



7. Bristles not longer than the plano-convex achenes; glumes reddish 

 brown, awn-tipped; shores and marshy ground throughout 111. 

 S. americanus Pers. 



4. Spikelets numerous in small clusters in compound umbels; plants peren- 

 nial with rhizomes, the terete stems 1-3 m. tall. 

 8. Achenes 2 mm. long, nearly as long as the glumes; spikelets ovoid, 

 5-10 mm. long; marshes and shallow water, throughout 111., except 

 the s. part S. validus Vahl 



8. Achenes 2.5-3 mm. long, shorter than the glumes; spikelets ellipsoid, 

 1-2 cm. long; shallow water in the n. half of the state. [5". occiden- 



talis (Wats.) Chase] 5. acutus Muhl. 



1. Involucral bracts several, foliaceous; stem 3-angled, leafy; plants perennial. 

 9. Spikelets 3-15 in an irregular umbel; rays 5-12, elongated, recurved- 

 spreading; spikelets ellipsoid, 1.5-4 cm. long; in the n. half of the state. 



S. fluviatilis (Torr.) Gray 



9. Spikelets numerous, umbellate or capitate. 

 10. Bristles downwardly barbed. 



11. Style 2-cleft; achenes plano-convex; bristles usually 4; spikelets 4- 



9 mm. long; swamps, rare. Lake Co., Gates 2770, 3059 



S. rubrotinctus Fern. 



11. Style 3-cIeft; achenes trigonal; bristles 6. 



12. Bristles twice the length of the achene; leaves 4-6 mm. wide; 

 spikelets 2.5-3 mm. long, commonly proliferous; wet ground 

 in woods in the s. half of the state S. polyphyllus Vahl 



