[Atrichum hercynicum (Hedw.) P. Beauv., moreBryum incurvum Huds. ex Brid., Catharinea hercynica F. Weber & D. Mohr, Catharinea hercynica var. sancta (Brid.) Brid., Catharinea sancta Brid., Catharinea sudetica C. Presl, Dicranum incurvum (Huds. ex Brid.) P. Beauv., Oligotrichum exiguum Stirt., Oligotrichum incurvum (Huds. ex Brid.) Lindb., Oligotrichum integrifolium Kindb., Orthotrichum hercynicum P. Beauv., Polytrichum hercynicum Hedw.]
Plants: bright green, somewhat glaucous, becoming reddish brown with age. Stems: 1–2.5(–3) cm. Leaves: 2.5–5 mm, lanceolate from a weakly sheathing base, broadly incurved and subtubulose when dry, somewhat spreading but remaining incurved and strongly channeled distally when moist; margins entire to finely and distantly serrulate; costa percurrent or shortly excurrent as a short mucro, the adaxial surface with several low continuous or interrupted abaxial lamellae; abaxial surface of lamina smooth or sporadically with scattered short lamellae near the apex of leaf; adaxial lamellae 8–20, 6–13 cells high, restricted to the costa, crispate-undulate, extending to the middle of the leaf or below, the margins finely and irregularly crenulate with bulging marginal cells, smooth; median cells of lamina 15–20 µm, somewhat smaller towards the margins, rounded subquadrate, thick-walled; marginal teeth distant, minute, unicellular; perichaetial leaves 3–3.5 mm, narrowly lanceolate. Seta: stout, pale brown, 2–4 cm. Capsule: 2–4 mm, cylindric, slightly larger at the base, terete or irregularly angled or ridged; peristome teeth 32, double, somewhat irregular. Spores: 10–15 µm.
Soil, gravel, and moist peaty embankments, open disturbed sites, roadcuts, beside paths, on lake shores, stream banks, late snow areas, also aquatic in rapidly flowing glacier melt streams. moderate to high elevations (500-2200 m). Greenland, Alta., B.C., Nfld. and Labr. (Nfld.), N.S., Yukon, Alaska, Mont., Oreg., Wash., Europe (southward to Spain, Turkey), e Asia (Japan).
An arctic-alpine species widespread in northern latitudes, Oligotrichum hercynicum is a pioneer species, typically forming bright green patches on disturbed soil but, like O. falcatum, also in aquatic habitats.