Herbs, perennial, to 115 cm; rhizomes absent; stolons present; corms present. Leaves emersed or submersed; submersed leaves phyllodial, flattened, 30--70 cm, rarely widening into blade; emersed leaves phyllodial, flattened, or petiole triangular, 34--50 cm, blade linear to elliptic, rarely hastate to sagittate, 5--15 ´ 0.6--12 cm, basal lobes when present shorter than remainder of blade. Inflorescences racemes, of 2--8 whorls, emersed, 8--10 ´ 2--6 cm; peduncles 10--115 cm; bracts connate more than or equal to ΒΌ total length, ovate, 3--6 mm, delicate, not papillose; fruiting pedicels absent. Flowers to 3 cm diam.; sepals recurved, not enclosing flower; filaments dilated, shorter than anthers, pubescent; pistillate sessile to subsessile, without ring of sterile stamens. Fruiting heads 1--1.7 cm diam.; achenes obovoid to oblong, abaxially keeled, 2--3 ´ 1.3--1.6 mm, beaked; face not tuberculate, wings 1--2, ± entire, glands 1; beak lateral, recurved, 0.8--1.4 mm. 2n = 22. Flowering summer (Jul--Sep). Calcareous or brackish shallow water and shores of ponds, swamps, and rivers, occasionally in deep water; 0--1000 m; Man., Ont., Que., P.E.I., Sask.; Ark., Calif., Conn., Del., D.C., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Nebr., N.H., N.J., N.Y., Ohio, Pa., R.I., Tenn., Vt., Va., Wash., W.Va., Wis.
Erect or lax, emersed or submersed, highly variable according to the habitat; lvs lanceolate and entire, or shortly sagittate with narrow basal lobes, or phyllodial; scape 1-8 dm, with 2-8 whorls of fls, typically geniculate at the lowest whorl, the upper fls staminate on filiform pedicels 1.5-3 cm, the lower pistillate, sessile or nearly so (the pedicel sometimes to 5 mm, rarely to 1 cm); bracts ovate, obtuse, 4-6 mm, connate below, smooth; sep ovate, 4-7 mm, reflexed at maturity; pet 1-3 cm; stamens 15-many; filaments subulate, roughened with minute scales; achenes obovate to oblong, 2-3 mm, narrowly winged on the margins only, usually with a resin-duct on each face; beak 0.8-1.4 mm; 2n=22. In shallow water of swamps and ponds; Me. and Que. to Minn., s. to Va., Tenn., Mo., and Neb. July-Sept. (S. heterophylla)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.