44. Sphagnum riparium Ångström, Öfvers. Kongl. Vetensk.-Akad. Förh. 21: 198. 1864.
Plants stiff and upright, large; green to pale green to brownish, capitulum large and flat, with a conspicuous terminal bud. Stems pale green, superficial cortex of 3-4 layers of weakly differentiated cells. Stem leaves triangular-lingulate, 1.2-1.4 mm; apex with a deep lacerate split; hyaline cells aporose, efibrillose and often septate. Branches unranked to rarely 5-ranked, branch leaves only weakly undulate, but sharply recurved at the apex, leaves not much elongated at distal end. Branch fascicles with 2 spreading and 2 pendent branches. Branch stem green, cortex enlarged with retort cells. Branch leaves ovate-lanceolate; 2-2.6 mm; straight; weakly undulate but strongly recurved, hyaline cells on convex surface with very large irregular pores (formed from the confluence of several smaller pores) at the cell apex, concave surface with large round wall thinnings in the cell angles; chlorophyllous cells triangular to trapezoidal in transverse section, apex normally slightly exposed on concave surface. Sexual condition dioicous. Spores 22-28 µm; proximal surface noticeably papillose, distal surface smooth or with fewer papillae; proximal laesura more than 0.5 the length of the radius.
Forming often extensive carpets in weakly minerotrophic mires; low to moderate elevations; Greenland; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Conn., Ind., Maine, Mass., Mich., Minn., Mont., N.H., N.J., N.Y., Ohio, Pa., Vt., Wash.; Eurasia.
Sporophytes are uncommon in Sphagnum riparium. This species is typically very easily recognized in the field with its pale green color, strong terminal bud, and unranked branch leaves.