Plants robust and weak-stemmed; green to golden-yellow; capitulum ± rounded in emergent forms, flat in submersed forms; lacking distinct terminal bud; Stems green to brown; superficial cortex of 2 layers of thin-walled and enlarged cells. Stem leaves triangular, 1--1.7 mm apex acute to slightly obtuse; leaves usually appressed; margins entire; hyaline cells fibrillose and usually septate at base and sides. Branches unranked, long and tapering, leaves greatly elongated at distal end. Branch fascicles with 2 spreading and 2 pendent branches. Branch stems green; cortex enlarged with conspicuous retort cells. Branch leaves ovate-lanceolate to lanceolate, 3--5.5 mm; straight$ but sometimes slightly falcate-secund; weakly undulate and recurved when dry; margins entire; hyaline cells on convex surface with 0--1 pore per cell, on concave surface with round wall thinnings on the apices and angles; chlorophyllous cells narrowly triangular in transverse section and just enclosed on the concave surface. Sexual condition dioicous. Spores 26--29 µm; both surfaces distinctly papillose, appearing pusticulate to irregularly pusticulate; proximal laesura mostly less than 0.5 spore radius.

Forming wet often floating carpets in weakly minerotrophic mires; N.B., Nfld., N.S., Que; Ala., Conn., Del., Fla., Ga., La., Maine, Md., Mass., Miss., N.H., N.J., N.Y., N.C., Pa., S.C., Vt., Va.

Sporophytes are uncommon. See discussion of S. atlanticum for taxonomic distinctions.