CYPEKACEAE. 175 



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. paiiciflorus. 

 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. caespitosus. 

 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. siibierminalis. 

 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. ffallii. 



Achene smooth or v"ery 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. Torreyi. 

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



13. S. mticronatuSt 

 Spikelets several or numerous, umbelled ; tall sedges. 



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

 Culm terete ; leaves reduced to shea'ths. 



Bristles downwardly barbed ; achene gray, abruptly mucronate. 



15. S. validus. 

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



1 6. S. Calif ornicus. 

 Spikelets several, spicate. 17. S. r it/us. 



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. 



1 8. S. interior. 

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



19. S. robust us. 

 Achene sharply 3-angled ; spikelets umbellate. 20. S. fl uviatilis. 



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



Spikelets narrowly cylindric, 2-5 cm. long; bristles 2-4. 21. S, Xor'ae-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. sy-lvaiicus. 



Spikelets 820 in each head; bristles not barbed below; scales acute. 



23. S. atrovirens. 

 Style 2-cleft ; achene plano-convex ' ? bristles 4. 24. S, microcarfus. 



