3. Oligotrichum hercynicum (Hedwig) Lamarck & de Candolle, Fl. Franç. ed. 3. 2: 492. 1805.
Polytrichum hercynicum Hedwig, Sp. Musc. Frond., 94. 1801; Oligotrichum incurvum (Bridel) Lindberg
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.