7. E. ovàta, R. Br. Culms nearly terete, 8–14´ high; spikelet globose-ovoid to ovate-oblong, obtuse, 1–6´´ long (dull brown); scales very obtuse, densely crowded in many ranks; style 3- (rarely 2-) cleft; achene obovate with narrow base, pale-brownish, shining, shorter than the 6–8 bristles, broader than the short-deltoid, acute and flattened tubercle. (E. obtusa, Schult.)—Muddy places, N. Brunswick to Minn., south and westward. Variable as to the length of its bristles. A low form, with smaller and more narrowly obovate achenes, and the bristles very short or none, is E. diandra, Wright. A dwarf form occurs with very small and few-flowered heads. (Eu.)
8. E. Engelmánni, Steud. Like the last; spikelets usually narrowly cylindrical and acute or acutish, 2–8´´ long; achene broad and truncate, the tubercle covering the summit; bristles not exceeding the achene. (E. obtusa, var. detonsa, Gray.)—Mass. to Penn. and Mo.
[+][+] Perennials, with running rootstocks.
9. E. olivàcea, Torr. (Pl. 2, fig. 1–5.) Culms flattish, grooved, diffusely tufted on slender matted rootstocks (2–4´ high); spikelet ovate, acutish, 20–30-flowered; scales ovate, obtuse, rather loosely imbricated (purple with a green midrib and slightly scarious margins); achene obovate, dull, abruptly beaked with a narrow tubercle, shorter than the 6–8 bristles.—Wet, sandy soil, Mass. to N. C., and western N. Y.
10. E. palsútris, R. Br. Culms nearly terete, striate, 1–5° high; spikelet oblong-lanceolate, pointed, many-flowered; scales ovate-oblong, loosely imbricated, reddish-brown with a broad and translucent whitish margin and a greenish keel, the upper acutish, the lowest rounded and often enlarged; achene rather narrowly obovate, somewhat shining, crowned with a short ovate or ovate-triangular flattened tubercle, shorter than the usually 4 bristles.—Very common, either in water, when it is pretty stout and tall, or in wet grassy grounds, when it is slender and lower. (Eu., Asia.)—Var. glaucéscens, Gray. Culms slender or filiform; tubercle narrower, acute, beak-like, sometimes half as long as the achene. With the type.—Var. cálva, Gray. Bristles none; tubercle short, but narrower than in the type.—Var. vìgens, L. H. Bailey. Culms very stout, rigid; achene more broadly obovoid. Lake Champlain and along the Great Lakes to Minn.
[*][*] Achene triangular or turgid; style 3-cleft.
[+] Bristles at least equalling the smooth achene, downwardly barbed, persistent.
11. E. rostellàta, Torr. Culms flattened and striate-grooved, wiry, erect (1–2½° high), the sterile ones reclining, rooting and proliferous from the apex (1–2° high), the sheath transversely truncate; spikelet spindle-shaped, 12–20-flowered; scales ovate, obtuse (light-brown); achene obovate-triangular, narrowed into the confluent pyramidal tubercle, which is overtopped by the 4–6 bristles.—Marshes, N. Eng. to S. C., west to Mich. and Ky.
12. E. intermèdia, Schultes. Culms capillary, wiry, striate-grooved, densely tufted from fibrous roots, diffusely spreading or reclining (6–12´ long); spikelet oblong-ovate, acutish, loosely 10–20-flowered (2–3´´ long); scales oblong, obtuse, green-keeled, the sides purplish-brown; achene obovoid with a narrowed base, beaked with a slender conical-awl-shaped distinct tubercle, which nearly equals the 6 bristles.—Wet slopes, Penn. to Iowa, north to Canada.
13. E. Torreyàna, Boeckl. Like the preceding, but more capillary and heads smaller (1½–2´´ long), sometimes proliferous, the one or more short new culms from the axil of its lowest scale, which persists as an herbaceous bract; achene very much smaller, with sharper angles and a short conical tubercle, which is hardly equalled by the 3–6 slender bristles. (E. microcarpa, var. filiculmis, Torr.)—Wet pine-barrens, N. J. to Fla.