Herbs, perennial, 4--21 cm (--100 cm when submersed). Leaves linear-attenuate, 1--10 cm (--40 cm when submersed), apex often subulate. Inflorescences: scape sheaths longer (shores) or shorter (submersed) than principal leaves, inflated; scapes linear to filiform, 1 mm wide, (4--)5--7-ribbed; mature heads white to pale gray, young heads dark, hemispheric to globose, 4--10 mm wide, soft, flattened when pressed; receptacle glabrous or rarely with a few clear hairs; involucral bracts becoming reflexed, obscured by proximal bracts and flowers, dark gray, broadly oblong to narrowly ovate or broadly obovate, 1--1.5 mm, margins entire, apex rounded, abaxially with white, club-shaped hairs, otherwise glabrous; inner and receptacular bracts gray to near black, oblanceolate or cuneate, 1.5 mm, margins entire, apex acute, distal margins and abaxial apical surface with white, club-shaped hairs. Staminate flowers: sepals 2, grayish, oblong-linear or linear-oblanceolate, curved, 1.5 mm, apex acute to rounded, margins and abaxial surface with white, club-shaped hairs; androphore club-shaped; petals 2, triangular, nearly equal, 0.5 mm, ciliate, hairs white, club-shaped; stamens 4; anthers black. Pistillate flowers: sepals 2, gray, oblong to narrowly obovate, curved, keeled, 1.5 mm, blade usually ciliate, distal abaxial surfaces with white hairs; petals 2, pale, oblong-linear to linear oblanceolate, 1.5 mm, apex acute to obtuse, apically ciliate, adaxially with white, club-shaped hairs; pistil 2-carpellate. Seeds light brown or red-brown, ovoid to broadly ellipsoid, 0.5 mm, very faintly reticulate, not papillate.
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Lvs very thin, often pellucid, 2–10 cm × 2–5 mm, 3–9-nerved with conspicuous cross-veinlets, tapering evenly from a pale, spongy-aerenchymatous base; scapes usually solitary for each rosette, 3–20 cm (or much longer in deep water), slender, slightly twisted, 5–7-ridged; mature heads subglobose, 4–6 mm thick, gray except for the exserted white-hairy tips of the tep and receptacular bracts; invol bracts ovate to obovate, obtuse, lustrous dark gray, glabrous, reflexed and concealed at maturity; receptacle glabrous; 2n=32. Usually in shallow water, occasionally in deeper water or on miry shores; Nf. to Minn., s. to Del. and Ind., and in the mts. to N.C.; also in Ireland and Scotland, where 2n=64. July–Sept. (E. articulatum; E. pellucidum; E. septangulare)
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