[+] Culm sharply triangular, stout, chiefly from running rootstocks; spikelets many-flowered, rusty brown, closely sessile in one cluster; sheaths at base more or less leaf-bearing.
5. S. púngens, Vahl. Running rootstocks long and stout; culm sharply 3-angled throughout (1–4° high) with concave sides; leaves 1–3, elongated (4–10´ long), keeled and channelled; spikelets 1–6, capitate, ovoid, usually long, overtopped by the pointed involucral leaf; scales ovate, sparingly ciliate, 2-cleft at the apex and awn-pointed from between the acute lobes; anthers tipped with an awl-shaped minutely fringed appendage; style 2-cleft (rarely 3-cleft); bristles 2–6, shorter than the obovate plano-convex and mucronate smooth achene.—Borders of salt and fresh ponds and streams, throughout N. Am. (Eu., S. Am.)
6. S. Torrèyi, Olney. Rootstocks slender if any (so that the plant is readily pulled up from the mud); culm 3-angled, with concave sides, rather slender (2–4° high), leafy at base; leaves 2 or 3, more than half the length of the culm, triangular-channelled, slender; spikelets 1–4, oblong or spindle-shaped, acute, distinct, pale chestnut-color, long overtopped by the slender erect involucral leaf; scales ovate, smooth, entire, barely mucronate; style 3-cleft; bristles longer than the unequally triangular-obovate very smooth long-pointed achene.—Borders of ponds, brackish and fresh, N. Eng. to Penn., Mich., and Minn.
7. S. Olnèyi, Gray. Culm 3-wing-angled, with deeply excavated sides, stout (2–7° high), the upper sheath bearing a short triangular leaf or none; spikelets 6–12, closely capitate, ovoid, obtuse, overtopped by the short involucral leaf; scales orbicular, smooth, the inconspicuous mucronate point shorter than the scarious apex; anthers with a very short and blunt minutely bearded tip; style 2-cleft; bristles 6, scarcely equalling the narrowly obovate plano-convex and mucronate achene.—Salt marshes, S. New Eng. to Fla., west to the Pacific.
S. mucronàtus, L. Resembling the last, 1–3° high; spikelets numerous in a dense cluster, oblong-ovate, 6–8´´ long or less; scales ovate, mucronate, firm, scarcely at all scarious; style 3-cleft; achene smaller, broadly obovate.—In a single locality in Delaware Co., Penn.; probably introduced from S. Europe.
[+][+] Culm triangular, tall and stout, from slender running rootstocks; spikelets many-flowered, loosely umbellate or corymbed, involucellate-bracted.
8. S. Cánbyi, Gray. Culm (3–5° high) 3-angled, usually sharply so above, obtusely below, the sheath at base extended into a long slender triangular and channelled leaf (2–4° long); involucral leaf similar (4–8´ long), continuing the culm; spikelets oblong (4–6´´ long), single or sometimes proliferously 2 or 3 together, nodding on the apex of the 5–9 long filiform and flattened peduncles or rays of the dichotomous umbel-like corymb, or the central one nearly sessile; scales loosely imbricated, oblong-ovate, acute, pale, thin and scarious, with a greenish nerved back; bristles 6, firm, furnished above with spreading hairs rather than barbs, equalling the slender abrupt beak of the obovate-triangular shining achene (1½´´ long).—In a pond near Salisbury, Md.
[+][+][+] Culm terete, very tall and stout, from a deep running rootstock, leafless or very nearly so; spikelets numerous, clustered in a one-sided compound umbel-like panicle longer than the involucral leaf; involucellate bracts small, scale-like and rusty-scarious; scales of the spikelets rusty or chestnut-brown, scarious, the midrib extended into a mucronate point.
9. S. lacústris, L. (Great Bulrush.) Culm 3–9° high, ½–1´ thick at base; spikelets ovate-oblong (3–4´´ long); scales mostly a little downy on the back and ciliate; style 2-cleft; achene pale and dull, obovate with a narrowed base, plano-convex, mucronate-pointed, usually overtopped by the 4–6 slender downwardly barbed bristles. (S. validus, Vahl.)—Common everywhere in still fresh water. (Eu., Asia, etc.)
[+][+][+][+] Culms slender from an annual root, terete, plano-convex or obtusely triangular, naked; the sheaths rarely bearing a short leaf; spikelets few or several in a sessile cluster, sometimes solitary, much overtopped by the involucral leaf; bristles often few or wanting.