CYPEEACEAE. 41 



flowered, the lower reflexed, the middle ones spreading, all separating from the 

 axis at maturity: scales green, several-nerved: achenes linear, 2.5-3 mm. long, 

 apiculate, 2-3 times as long as thick, as long as the scale. Susquehanna 

 valley. Common, on the dry river shores and islands. Schists. Sum. 

 11. O. filiculmis Vahl. Perennial. Leaf -blades 2-4 mm. wide: scape smooth, 

 slender, often wiry, ascending or reclined, 1.5 dm. long: spikelets densely 

 clustered in a sessile head, or in 1-7 peduncled heads, linear, acute, 5-11- 

 flowered, subterete or compressed, 5-12 mm. long, 2 mm. wide or less: scales 

 pale-green, 7-11-nerved, appressed: achenes oblong or obovoid, fully 2 mm. 

 long, 3-angled, dull gray, about twice as long as thick. S. Occasional, in 

 sand near Peach Bottom. 



3. EBIOPHORUM L. Bog herbs, perennial by rootstocks. Stems erect, 

 triangular or nearly terete. Leaves with linear blades, or 1 or 2 of the upper 

 mere bladeless sheaths. Spikelets terminal, solitary, capitate, or in umbels, 

 subtended by an involucre of 1-several bracts, or naked. Scales spirally imbri- 

 cate, usually all flower-bearing. Perianth of 6 or many, filiform smooth soft 

 bristles, white or brown, the bristles straight or crisped, much exserted. Sta- 

 mens 1-3. Style deciduous. Stigmas 3. Achene 3-angled, often broad. 



1. E. virginicum L. Stems stiff, smooth, 4-12 dm. tall: leaf -blades narrowly 

 elongate-linear, flat: bracts of the involucre spreading or deflexed: spikelets 

 several or numerous in a dense terminal cluster, erect, or the outer spreading: 

 scales acute, brown with a green center: perianth-bristles numerous, dingy- 

 brown or copper-colored, about 3 times as long as the scale: achenes linear- 

 oblong, acute, apiculate, brown. E. S. Common in swamps. Quartzite, 

 schists. Sum. COTTON-GRASS. 



4. SCIE.PUS [Tourn.] L. Annual or perennial small or large caulescent 

 or scapose herbs, the leaves sometimes reduced to basal sheaths. Spikelets few- 

 many-flowered, terete or flattened, solitary, capitate, spicate, or umbellate, often 

 subtended by an involucre. Scales spirally imbricate or nearly 2-ranked, the 

 1-3 lower sometimes empty. Perianth of 1-6 slender or rigid bristles or rarely 

 wanting. Stamens 2 or 3. Style not swollen at the base, wholly deciduous 

 from the achene, or its base persistent. Stigmas 2 or 3. Aehene triangular, 

 lenticular or plano-convex. BULRUSH. CLUB-RUSH. 



Involucre of a single bract, or wanting. 



Spikelets solitary, terminal. 1. 8. planifolius. 



Spikelets typically several or numerous, often apparently 



lateral. 

 Spikelets few, 1-12, appearing lateral. 



Scapes bluntly 3-angled : plants annual. 2. S. debills. 



Scapes acutely 3-angled : plants perennial. 3. 8. americanus 



Spikelets several or numerous, in umbels or umbel- 

 like clusters. 4. 8. validus. 

 Involucre of 2 or more bracts with flat blades. 



Spikelets relatively large, few-several, capitate or umbel- 

 late. 5. S. fluviatilis. 

 Spikelets relatively small, very numerous, umbellate. 



Perianthl-bristles downwardly barbed, or wanting : 



spikelets in umbellate heads. 

 Perianth-bristles equalling the achene or slightly 



exceeding it : leaf-blades 6-16 mm. wide. 

 Spikelet-scales obtuse : perianth-bristles barbed 



throughout. 6. S. sylvaticus. 



Spikelet-scales acute : perianth-bristles barbed 



above. 7. 8. atrovirens. 



Perianth-bristles twice as long as the achene : 



leaf-blades 4-6 mm. wide. 8. 8. polyphyllua. 



Perianth-bristles smooth or merely pubescent : umbel 



decompound. 



Spikelets sessile, borne in small heads. 9. 8. cyperinus. 



Spikelets, or some of them, distinctly peduncled. 10. 8. Eriovhorum. 



