Hypnum serpens var. compactum Hooker in T. Drummond, Musc. Amer., 188. 1828; Amblystegium americanum Grout; A. compactum (Hooker) Austin; A. dissitifolium Macoun & Kindberg; A. holzingeri (Grout) Grout; A. subcompactum Macoun & Kindberg; Brachythecium collinum var. holzingeri Grout; H. compactum (Hooker) Müller Hal.; Rhynchostegiella compacta (Hooker) Loeske; R. compacta subsp. americana (Grout) Wijk & Margadant

Plants in dense to ± loose mats. Stems erect-ascending or creeping; pseudoparaphyllia foliose or filamentous. Stem leaves crowded, homomallous when dry, gradually narrowed to apex, slightly concave; alar cells usually many, region reaching from margin to costa at insertion or nearly so; laminal cells 5-9:1; basal cells shorter, broader. Specialized asexual reproduction by papillose rhizoidal gemmae on abaxial costa surface. Perichaetia with inner leaves ± suddenly narrowed to apex, not plicate, margins irregularly denticulate distally, apex acuminate, laminal cells smooth. Seta orange-yellow or at base reddish, 0.8-1.4 cm. Capsule with annulus separating, 1- or 2-seriate; operculum conic to short-rostrate; exostome teeth lanceolate, brownish yellow, external surface reticulate or reticulate-striate basally or with portions cross striolate; endostome cilia to 1/2 segment length. Spores finely papillose.

Damp cliffs, limestone, swamps on logs, stumps, humus, bark at base of trees; low to high elevations; Greenland; Alta., B.C., Man., Nfld. and Labr. (Nfld.), N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon; Alaska, Ariz., Ark., Calif., Colo., Idaho, Ind., Iowa, Kans., Mich., Minn., Mo., Mont., Nebr., Nev., N.Mex., N.Y., N.Dak., Ohio, Pa., S.Dak., Tex., Utah, Va., Wash., W. Va., Wis.; Mexico (Baja California, Puebla); Central America (Guatemala); n, c Europe; Asia (Kashmir); Atlantic Islands (Iceland).