CYPERACEAE 



177 



Scapes triangular : upper sheath with a linear blade : perianth-bristles 



upwardly barbed. 3. S. Clintonii. 



Perianth-bristles wanting : scales keeled. 4. S. carinatus. 



Spikelets normally more than 1, usually several or numerous, often apparently 



lateral. 

 Spikelets few, 1-12, appearing lateral. 



Scapes not sharply 3-angled : plants annual. 



Achene strongly transverse-rugose : perianth-bristles wanting. 5. S. Hallii. 



Achene smooth or very slightly roughened : perianth-bristles 4-6. 6. S. debilis. 



Scapes sharply 3-angled :" plants perennial by rootstocks. 



Spikelets acute : scales awned : involucral bract much surpassing the 



inflorescence. 7. S. Americanus. 



Spikelets obtuse : scales mucronate : involucral bract only slightly sur- 

 passing the inflorescence. 8. S. Olneyi, 

 Spikelets several or numerous, in umbels or umbel-like clusters. 



Scapes sharply 3-angled : leaves with blades about as long as the scape. 9. 5. cylindricus. 

 Scapes terete : leaves reduced to mere sheaths. 



Perianth-bristles downwardly barbed : achene gray, abruptly mucronate. 10. S. lacustris. 

 Perianth-bristles short-plumose below : achene nearly white, nar- 

 rowed above. 11. S. Calif ornicus. 

 Involucre of 2 or more bracts with flat blades. 

 Spikelets not in dense globular heads. 



Spikelets few to several, capitate to umbellate, relatively large. 



Spikelets in simple clusters : achenes obovoid-oblong, pale brown. 12. S. campestris. 



Spikelets in often compound clusters : achenes orbicular-obovoid, dark 



brown. 13. S. robustus. 



Spikelets very numerous, in compound umbels or umbelled heads, relatively 



small. 

 Perianth-bristles downwardly barbed, or wanting : spikelets in umbelled 



heads. 

 Perianth-bristles present. 



Perianth-bristles equalling or slightly exceeding the achene : leaf- 

 blades 6-16 mm. wide. 

 Spikelets 3-8 in each head : scales obtuse : perianth-bristles barbed 



throughout. 14. S. $ylvaticus. 



Spikelets 8-20 in each head : scales acute : perianth-bristles not 



barbed below. 15. S. atrovirens. 



Perianth-bristles twice as long as the achene : leaf-blades 4-6 mm. 



wide. 16. S. polyphyllus. 



Perianth-bristles wanting. 17. S. Georgianus. 



Perianth-bristles smooth or slightly pubescent : umbel mostly decompound. 

 Perianth-bristles shorter than the scales or scarcely exceeding them. 

 Perianth-bristles about as long as the achene : scales rather acute. 

 Inflorescence merely terminal : spikelets 1 mm. thick : achenes 



not papillose. 18. S. divaricatus. 



Inflorescence terminal and lateral: spikelets 2-3 mm. thick 



achenes papillose. 19. S.fontinalis. 



Perianth-bristles much longer than the achene : scales mucronate. 20. /S. lineatus. 

 Perianth-bristles much exsertedt beyond the scales at maturity 



Spikelets sessile, in small heads. 21. S. cyperinus. 



Spikelets, at least some of them, distinctly peduncled. 22. S. Eriophorum. 



Spikelets very numerous in one or several dense globular heads. 23. S. Cubensis. 



1. Scirpus nanus Spreng. Annual. Roots fibrous : scapes filiform, flattened, 

 grooved, tufted, erect or ascending, 2-5 cm. high, each bearing a scarious bladeless sheath 

 near the base : spikelets solitary, terminal, ovoid-oblong, rather acute, 3-8-flowered, 2-3 

 mm. long, not subtended by a bract : scales ovate or lanceolate, pale green, the lower ob- 

 tuse, the upper subacute : p'erianth-bristles about 6, downwardly barbed, longer than the 

 achene : stigmas 3: achenes oblong, 1 mm. long, 3-angled, pale, pointed at each end. 



In muddy places in salt marshes, Cape Breton Island to Florida and Texas and about salt springs 

 in New York and Michigan. Also on the Pacific coast of North America and on the coasts of Europe. 

 Summer and fall. 



2. Scirpus caespitosus L. Perennial. Scapes smooth, terete, densely tufted, light 

 green, erect or ascending, almost filiform, wiry, 10-40 cm. long : basal sheaths numerous, 

 membranous, imbricated, acuminate, the upper one bearing a short very narrow blade : 

 spikelet solitary, terminal, few-flowered, ovoid-oblong, about 4 min. long, subtended by a 

 subulate involucral bract of about its own length : scales yellowish brown, ovate, obtuse or 

 subacute, deciduous : perianth-bristles 6, smooth, longer than the achene : stigmas 3 : 

 achenes oblong, 1.5 mm. long, 3-angled, smooth, brown, acute. 



In bogs and on moist rocks, Greenland to Alaska, south to the mountains of New England, the 

 Adirondacks, western New York, Illinois. Minnesota and British Columbia, in the Rooky Mountains to 

 Colorado, and on the higher summits of the southern Alleghenies. Also in Europe and Asia. Summer. 



3. Scirpus Clintonii A. Gray. Perennial. Scapes tufted, triangular, very slender, 

 erect, 10-40 cm. tall, roughish on the angles : lower sheaths imbricated, one or more of 

 them bearing short subulate blades, the upper one bearing a flat, narrowly linear blade 

 shorter than the stem : spikelet solitary, terminal, ovoid, few-flowered, 3-4 mm. long, sub- 

 tended by a subulate involucral bract*: scales ovate, pale brown, acute : perianth-bristles 

 3-6, filiform, upwardly barbed, as long as the achene or longer : stigmas 3 : achenes oblong, 

 1.5 to nearly 2 mm. long, sharply 3-angled, brown, smooth, ohtnse. 



In dry fields and thickets, New Brunswick to Michigan and North Carolina. Local. Summer. 

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