Bryum marginatum Dickson ex Withering, Syst. Arr. Brit. Pl. ed. 4, 3: 824. 1801; Mnium serratum Schrader ex Bridel

Plants (1-)2-3(-6) cm. Stems red or reddish brown. Leaves green to dark green, contorted and twisted when dry, ovate-elliptic or sometimes elliptic or oblong-ovate, rarely narrow, (2-)3-4(-5) mm; base long-decurrent; margins reddish brown, 2-stratose or rarely multistratose, toothed to below mid leaf or sometimes only distally, teeth paired or occasionally single, small to large, blunt or occasionally sharp; apex acute or acuminate, rarely obtuse or rounded, apiculate or cuspidate, cusp toothed; costa percurrent, subpercurrent, or excurrent, smooth, on well-developed leaves distal abaxial surface rarely with few blunt teeth; medial laminal cells ± isodiametric or short-elongate, (18-)20-30(-40) µm, slightly smaller towards margins, in diagonal or longitudinal rows, usually strongly collenchymatous, blue postmortal color absent; marginal cells linear, in 2-3(-4) rows. Sexual condition synoicous or rarely dioicous. Seta single. Capsule yellow-brown, 2-4 mm; operculum rostrate; exostome reddish brown, sometimes yellowish. Spores 18-32 µm.

Capsules mature late spring. Forests on humus, soil, logs, rock, base of trees, shaded cliffs; low to moderate elevations; Greenland; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Ga., Idaho, Ill., Iowa, Ky., Maine, Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.Mex., N.Y., N.C., N.Dak., Ohio, Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W. Va., Wis., Wyo.; Europe; Asia; Africa.

Mnium marginatum is a widespread species that should only be confused with the closely related 4. M. lycopodioides; see discussion under that species.