Stems 7--10(--18) mm, slender, rather wiry. Leaves 1.5--1.8(--2.5) mm, ovate to oblong-obovate, erect-incurved when dry, only weakly spreading when moist, rounded concave in lamellate portion, becoming abruptly cucullate approaching the obtuse apex; margins irregularly dentate with projecting ends of obliquely oriented, rhomboidal marginal cells, usually hyaline-margined; costa ending in or just below apex, smooth on the back above, rarely with a few low, adaxial lamellae; lamellae 8--15, 6--12 cells high, margins deeply incised, coarsely and irregularly dentate; cells of leaf base short-rectangular, narrower at margins; median cells of lamina 12--24(--30) µm wide, thin- to firm-walled; perichaetial leaves 3.8--4.5 mm, erect, twice as long as stem leaves or longer. Seta brown, 7--15 mm. Capsule 2.6--4 mm, greenish to dark brown to blackish brown, variable in shape, asymmetrically ovoid and gibbous; peristome teeth 200--320 µm.

Habitat similar to that of P. cavifolium, somewhat rare and local in Arctic North America; Nunavut (Baffin Is.), Labrador, Yukon; Arctic Alaska (including Aleutians); Arctic and subarctic Eurasia (southward to 61ºN, including Archangelsk Province, e Siberia, Altai); Atlantic Islands (Iceland).