10. S. débilis, Pursh. (Pl. 3, fig. 1–5.) Culms obtusely triangular, with somewhat hollowed sides, 1–2° high, yellowish-green, shining; spikelets 3–12, capitate, ovate-oblong, obtuse (3–4´´ long), chestnut-brown; involucral leaf often horizontal at maturity; scales roundish; stamens 3; style 2–3-cleft; bristles 6, stout, downwardly barbed, equalling or two surpassing the obovate turgidly plano-convex (or bluntly 3-sided) abruptly mucronate-pointed smoothish achene.—Swamps, Mass. to S. C., Minn. and Neb. Aug., Sept.
11. S. Smíthii, Gray. Culms terete, slender, 3–12´ high, often leaf-bearing from the upper sheath, dull green as are the 1–3 oblong-ovate acute spikelets; involucral leaf always erect; scales oblong-oval; style 2-cleft; bristles 1 or 2 minute rudiments or none; achene somewhat lenticular, smooth, deciduous with the scales.—Wet shores, Delaware Bay to L. Ontario, Mich., N. Ind., and Ill. July.
12. S. supìnus, L., var. Hállii, Gray. Culms filiform, 5–12´ high; upper sheath rarely distinctly leaf-bearing; spikelets 1–7 in a sessile or sometimes geminately proliferous cluster, ovate-oblong becoming cylindrical, greenish; scales ovate, strongly keeled, mucronate-pointed; stamens 2 or 3; style 2-cleft; bristles none; achene obovate-orbicular, mucronate, plano-convex, strongly wrinkled transversely.—Wet shores, Ill. to Tex.; also found in E. Mass. (Hitchings). (Eu.)
[*][*][*] Spikelets in simple or mostly compound umbellate or cymose-panicled clusters, many-flowered, terete; involucre of mostly several flat leaves; culm tall, from tufted or running rootstocks, triangular, leafy, sedge-like; leaves rough on the margin; style mostly 3-cleft.
[+] Spikelets large (6–15´´ long); midrib of the scales extended beyond the mostly lacerate or two-cleft apex into a distinct awn.
13. S. marítimus, L. (Sea Club-Rush.) Leaves flat, linear, as long as the stout culm (1–3° high), those of the involucre 1–4, very unequal; spikelets few–several in a sessile cluster, and often also with 1–4 unequal rays bearing 1–7 ovate or oblong-cylindrical (rusty-brown) spikelets; awns of the scales soon recurved; achene obovate-orbicular, compressed, flat on one side, convex or obtuse-angled on the other, minutely pointed, shining, shorter than the 1–6 unequal and deciduous (sometimes obsolete) bristles.—Saline localities, on the coast from N. Scotia to Fla., and in the interior across the continent. (Eu.)—Var. macrostáchyos, Michx.; larger, with very thick oblong-cylindrical heads (1–1½´ long), and longer involucral leaf (often 1° long).
14. S. fluviátilis, Gray. (River C.) Culm very stout, 3–5° high; leaves flat, broadly linear (½´ wide or more), tapering gradually to a point, the upper and those of the very long involucre very much exceeding the compound umbel; rays 5–9, elongated, recurved-spreading, each bearing 1–5 ovate or oblong-cylindrical acute paler heads; scales less lacerate and awns less recurved; achene obovate, sharply and exactly triangular, conspicuously pointed, opaque, scarcely equalling the 6 rigid bristles.—Borders of lakes and large streams, W. Vt. to Conn. and Penn., west to Minn. and Iowa.
[+][+] Spikelets very numerous, small (1–3´´ long); scales mucronate-pointed or blunt; umbel-like cymose panicle irregular, compound or decompound; culm 2–5° high, unusually leafy; leaves broadly linear, green and rather soft; bristles very slender, often more or less tortuous and naked below.
15. S. sylváticus, L. Spikelets lead-colored, clustered 3–10 together at the end of the mostly slender ultimate divisions of the open decompound panicle, ovoid or lance-ovate, 2´´ long; scales bluntish; bristles 6, downwardly barbed throughout, rather exceeding the triangular short-pointed achene; style 3-cleft.—Along brooks, E. Mass. to N. Y.; rare.
Var. dígynus, Boeckl. Style 2-cleft and the achene not at all angled on the back; stamens 2, and bristles 4. (S. microcarpus, Presl.)—N. Scotia and N. Eng. to Minn., and westward.