Plants moderate-sized to robust, fairly weak-stemmed, lax in submersed forms, ± sprawling in emergent froms; golden-brown to dark brown; capitulum weakly 5-radiate, branches strongly laterally curved; golden brown to dark brown. Stems pale brown, superficial cortex of only weakly differentiated. Stem leaves triangular-lingulate, 0.8--1.3 mm, usually appressed; apex acute to narrowly obtuse, hyaline cells nonseptate and fibrillose near apex. Branches unranked or weakly 5-ranked, typically strongly curved, leaves moderately elongated at distal end. Branch fascicles with 2 spreading and 1--2 pendent branches. Branch stems green$ but sometimes reddish at proximal end, with cortex enlarged with conspicuous retort cells. Branch leaves 2--2.8 mm, ovate-lanceolate to narrowly ovate-lanceolate, 2--2.8 mm; straight to usually strongly subsecund; weakly undulate and recurved; margins entire; hyaline cells on convex surface often with 2 pores per fibril interval, pores less than 1/3 cell diameter; concave surface aporose or rarely with a few wall thinnings in cell ends and angles; chlorophyllous cells trapezoidal in transverse section and narrowly exposed on concave surface. Sexual condition dioicous. Spores 33--38 µm; both surfaces roughly verrucate-scabrate; proximal laesura less than 0.5 spore radius.

Forming wet carpets$ but habitat unclear due to recent taxonomic separation from S. norvegicum; in North America, S. majus seems to occur in ombrotrophic to poor fen habitats, often on floating mats, mixed with S. cuspidatum in eastern North America; B.C., Nfld., N.S., Ont., Que., Alaska, Conn., Maine, Mass., Mich., Minn., N.H., N.J., Pa., Vt., Wis.; Eurasia.

Sporophytes are rare. In the field S. majus is typically darker brown than S. norvegicum, while its capitulum is denser and less stellate appearing than the latter species. See also discussion of S. annulatum.