CYPERACEAE. 1 75 



deciduous from the achene, or its base persistent as a subulate tip. Achene tri- 

 angular, lenticular or plano-convex. [Latin name of the Bulrush, said to be from 

 sirs, the Celtic word for rushes.] About 200 species of very wide geographic dis- 

 tribution. Besides the following, some 6 others occur in the southern and western 

 parts of North America. 



Spikelet solitary, terminal, bractless or subtended by a single bract or short leaf. 

 No involucral bract. 



Culms 2-5 cm. high ; achene smooth ; plant of saline soil. i. S. nanus. 

 Culms 7-25 cm. high ; achene reticulated ; plant of fresh-water marshes. 



2. S. pauciflorus. 

 Involucral bract present, erect. 



Bract shorter than or but little exceeding the spikelet ; plants not aquatic. 

 Culm terete ; leaf of upper sheath subulate ; bristles smooth. 



3. S. cacspitostts. 

 Culms triangular ; leaf of upper sheath linear ; bristles upwardly barbed. 



Leaves shorter than the culm ; scales acute, 4. S. Clintoni. 



Leaves about as long as the culm ; scales cuspidate. 



5. S. planifolius. 

 Bract at least twice as long as the spikelet ; plant aquatic. 



6. S. subterminalis. 

 Spikelets normally more than i, usually several or numerous, often appearing lateral ; 



involucral bract only i. 

 Spikelets few, 1-12, appearing lateral. 



Culms not sharply 3-angled ; achene plano-convex ; annuals. 



Achene strongly transversely rugose. 7. S. Hallii. 



Achene smooth or very slightly roughened. 



Bristles downwardly barbed, about equalling the achene. 



8. S. debilis. 



Bristles minute or wanting. 9. S. Smithii* 



Culms sharply 3-angled ; plants perennial by rootstocks. 



Achene plano-convex ; bristles shorter than or equalling the achene. 



Spikelets acute, much overtopped by the slender involucral leaf ; scales 



awned. 10. S. Americanus. 



Spikelets obtuse ; involucral leaf short, stout ; scales mucronulate. 



11. S. Olneyi. 

 Achene 3-angled, ridged on the back. 



Bristles longer than the achene; involucral leaf erect. 



12. S. Torreyt. 

 Bristles as long as the achene ; involucral leaf abruptly bent. 



13. S. mucronatus, 

 Spikelets several or numerous, umbelled ; tall sedges. 



Culm sharply triangular, equalled by the long leaves. 14. S. cylindricus. 

 Culm terete ; leaves reduced to sheaths. 



Bristles downwardly barbed ; achene gray, abruptly mucronate. 



15. S. lacustris. 

 Bristles short-plumose below ; achene nearly white, narrowed above. 



16. S, Califomicus. 

 Spikelets several, spicate. 17. S. rufus. 



Spikelets several, capitate or umbellate, large ; involucral leaves 2 or more. 

 Achene lenticular or plano-convex ; spikelets capitate. 



Capitate cluster simple ; achene obovate-oblong, pale brown. 



18. S. campestris. 

 Capitate cluster often compound ; achene orbicular-obovate, dark brown. 



19. S. robustus. 

 Achene sharply 3-angled ; spikelets umbellate. 20. S. fluviatilis. 



Spikelets oblong-cylindric, 1.5-2.5 cm. long; bristles 6. 



Spikelets narrowly cylindric, 2-5 cm. long ; bristles 2-4. 21. S. Novae- Angliae. 

 Spikelets very numerous in compound umbels or umbelled heads, small ; involucral leaves 



several ; tall sedges. 



Bristles downwardly barbed ; spikelets in umbelled heads. 

 Spikelets ovoid or oblong, 3-5 mm, long. 



Bristles equalling or slightly exceeding the achene ; leaves 6-16 mm. wide. 

 Style 3-cleft ; achene 3-angled ; bristles 6. 



Spikelets 3-8 in each head ; bristles barbed throughout ; scales 



obtuse. 22. S. sylvaticus. 



Spikelets 8-20 in each head; bristles not barbed below; scales acute. 



23. S. atrovirens. 

 Style 2-cleft ; achene plano-convex ; bristles 4. 24. S. microcarpus. 



