Plants moderate-sized, typically stiff and compact, capitulum usually hemispherical; green, grayish white, pale yellow, purplish red, may have a slight metallic luster when dry. Stems pale green or yellowish, rarely red-tinged; superficial cortical cells mostly aporose, but some cells may have a single oval to elliptic pore-like wall thinning in the distal portion of the cell. Stem leaves triangular to triangular-lingulate, 1-1.3 mm, apex acute to slightly obtuse, border broad at base (more than 0.25 width); hyaline cells narrowly rhomboid, mostly 0-1-septate and mostly efibrillose. Branches usually strongly 5-ranked. Branch fascicles with mostly 3 spreading and 1-2 pendent branches. Branch leaves ovate to ovate-lanceolate, 1.1-1.5 mm, concave, straight, apex slightly involute; hyaline cells on convex surface with numerous oval to elliptic pores along commissures grading from small pores near apex to large round pores at base, concave surface with large round pores in proximal portions of leaf. Sexual condition monoicous or dioicous. Spores 19-27 µm, finely papillose on proximal surface, pusticulate on distal surface; proximal laesura less than 0.4 spore radius.
Capsules mature mid summer. Weakly minerotrophic and hygrophytic, wet mineral bedrock, damp coniferous humus along coast and in montane regions; low to high elevations; B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que.; Alaska, Conn., Ga., Maine, Md., Mass., Minn., N.H., N.Y., N.C., Pa., Tenn., Vt., Va., W.Va.; Eurasia.
Sporophytes are common in Sphagnum quinquefarium. This species is usually associated with S. capillifolium, S. girgensohnii, and S. russowii. No other species of sect. Acutifolia has the combination of quinquefarious branch leaves and three spreading branches per fascicle. Sphagnum rubiginosum has three spreading branches but the branch leaves are quite unranked and its lingulate stem leaf is quite distinct from the triangular stem leaf of S. quinquefarium. See also discussion under 86. S. talbotianum.