Plants slender and weak-stemmed, moderate-sized, flaccid and plumose when submerged and stiffer and more compact when emergent; green to yellow, usually not tinged with brown or red; capitulum well defined, flat in submersed forms and more rounded in emergent forms. Stems green; superficial cortex of 2-3 layers of enlarged thin-walled cells. Stem leaves long triangular-ovate, 1-2 mm; usually appressed; apex acute to apiculate, hyaline cells only rarely septate or aporose but often fibrillose in apical region. Branches unranked, straight to slightly curved, leaves somewhat elongated at distal end. Branch fascicles with 2 spreading and 2-3 pendent branches. Branch stems green, cortex enlarged with conspicuous retort cells. Branch leaves 1.5-2.7 mm, ovate-lanceolate to lanceolate; straight to falcate toward branch tips; when dry often undulate and lightly recurved, margins entire to rarely weakly toothed along the margins in flaccid aquatic forms, hyaline cells on convex surface with 0-1 small round pores at apex, on concave surface with faint round wall thinnings in cell apices and angles; chlorophyllous cells triangular to trapezoidal in transverse section, broadly exposed on the convex surface and exposed slightly to broadly on the concave surface. Sexual condition dioicous. Spores 30-43 µm; the superficial surface coarsely papillose to papillose reticulate.

Widespread, forming wet carpets in weakly minerotrophic mires; low to moderate elevations; Nfld. and Labr. (Nfld.), N.S.; Ala., Conn., Del., Fla., Ind., Maine, Mass., Mich., Minn., N.H., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Vt., Va.; Europe.

The sporophytes of Sphagnum viride are uncommon. See discussion under 27. S. cuspidatum for taxonomic distinctions. Spore characters are taken from Flatberg’s description.