Plants: robust, stiff; green, pale green, yellow-green; large terminal bud; typically as loose carpets in coniferous forests. Stem: green to red-brown; 2–3 superficial cortical layers. Stem: leaves shorter than branch leaves, ovate-lingulate to oblong-lingulate, 1.6–1.8 × 1–1.2 mm; hyaline cells mostly nonseptate. Branches: long and tapering with distinct squarrose spreading leaves, often terete in tundra forms. Branch: fascicles with 2 spreading and 2–3 pendent branches. Branch: stems with 1–2 layers of cortical cells. Branch: leaves larger than stem leaves, 1.9–2.8 mm, conspicuously squarrose from ovate-hastate base and abruptly narrowed 1/2–1/3 distance from apex into involute-concave acumen, often terete in tundra forms; hyaline cells convex on both surfaces, non-ringed pores at ends and corners of cells, ringed pores on concave surface (4–8/cell) and nonringed pores (2–4/cell) on convex surface, internal commissural walls smooth or indistinctly papillose, chlorophyllous cells ovate triangular with widest part at or close to the convex surface. Sexual: condition monoicous. Spores: 17–30 µm; proximal surface finely papillose, distal surface smooth with raised bifurcated Y-mark sculpture; proximal laesura more than 0.5 spore radius. Phenology: Sporophytes abundant, capsules mature early to mid summer.
Forming loose carpets in rich habitats such as wet coniferous forests, Thuja swamps, karrs, medium fens, and stream margins. low to high elevations. Greenland, Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon, Alaska, Ariz., Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mont., N.H., N.J., N.Y., N.C., Oreg., Pa., S.D., Tenn., Vt., Wash., W.Va., Wis., Wyo., Eurasia, Pacific Islands (New Zealand).
In its typical robust form with strongly squarrose branch leaves, Sphagnum squarrosum is unmistakeable. Smaller forms such as occur in the higher mountains may be difficult to identify accurately without careful examination of microscopic details. In the tundra there sometimes occur large, terete forms of S. squarrosum but these are usually considerably more robust than S. teres. See also discussion under 14. S. strictum.