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FLORA OF THE DISTRICT OF COLUMBIA. 97 



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



Spikelets large, about 2 cm. long at maturity, ovate. Scales awn-tipped. 



Achenes sharply 3-angled; spikelets numerous, in a compound umbel. 



6. S. fluviatllis. 

 Achenes plano-convex; spikelets few to several, in simple or nearly simple umbels. 



7. S. robustus. 

 Spikelets not over 8 mm. long, very numerous, in decompound umbels. 

 Spikelets pedicellate, in loose clusters in large drooping panicles, or if in dense 

 glomerules the spikelets woolly from the long smooth delicate bristles. 

 Spikelets cylindric, 6-8 mm. long, in loose panicles; bristles not exserted 



beyond the scales 8. S. lineatus. 



Spikelets ovate or subglobose, not over 5 mm. long, woolly from the exserted 

 bristles. 

 Spikelets mostly in glomerules of 3-5. 



Glomerules not congested in dense heads 9. S. cyperinus. 



Glomerules congested in dense heads 9a. S. cjrperinus condensatus. 



Spikelets solitary, or in small clusters with pedicellate lateral spikelets. 



10. S. eriopliorum. 

 Spikelets sessile (not over 5 mm. long), in dense glomerules, these in stiff -rayed 

 decompound umbels; bristles shorter than the scales. 

 Spikelets ruddy brown, commonly proliferous. Bristles fiexuous, much longer 



than the achenes 11. S. polyphyllus. 



Spikelets olive or greenish brown. 

 Spikelets 3-8 in each glomerule; umbel loose and drooping. 



12. S. sylvaticus. 

 Spikelets several to many, in dense glomerules; rays of the umbel stiff. 



Sheaths and often the leaves nodulose; bristles as long as the achenes. 



13. S. atrovirens. 

 Sheaths not nodulose; bristles short or wanting 14. S. georgianus. 



1. Scirpus planifolius Muhl. 



Rocky woods; common from Cleveland Park north and west and along Sligo Creek, 

 below Takoma Park. Apr.-June. Vt. to Md. and Mo. 



2. Scirpus debilis Pursh. 



Wet sandy open ground and mud flats; frequent near the Eastern Branch and 

 Potomac; also at Terra Cotta. July-Sept. Eastern U. S. 



3. Scirpus smithii A. Gray. 



Wet shores; beach of Hunting Creek, near Alexandria. July-Sept. Me. to Va. and 

 Mich. 



4. Scirpus americanus Pers. 



Open marshy ground in the flood plain of the Potomac, from Long Bridge south- 

 ward; infrequent. June-Oct. Throughout the U. S. (S. pungensYahl.) 

 6. Scirpus validus Vahl. Bulrush. 



Marshes and shallow water in the flood plain of the Eastern Branch and Potomac, 

 forming a pure growth; infrequent. June-July. Throughout the U. S. 



6. Scirpus fluviatilis (Torr.) A. Gray. River club rush. 

 Marshes; near the mouth of Eastern Branch and at Dyke. June- July. Northern 



states, south to Va. 



7. Scirpus robustus Pursh. 



Marshes along the Potomac below Alexandria; "Maltox Creek." June. Atlantic 

 Coastal Plain. 



8. Scirpus lineatus Michx. 



Swales and moist wood borders; frequent along the Potomac. June. Eastern U. S. 



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