Plants: small, bright green. Stems: with apices not distinctly hooked, branches many. Leaves: often somewhat incurved, appressed, not falcate-secund, strongly concave, 2-plicate, 0.8–1.3 mm; apex abruptly acute to short-acuminate; medial laminal cells pellucid. Phenology: Capsules mature Jun–Aug.
Dry siliceous boulders, calcareous rock, mineral soil, subalpine-alpine. moderate to high elevations (900-4000 m). Alta., B.C., Nfld. and Labr., Que., Yukon, Ariz., Calif., Colo., Idaho, Oreg., Utah, Wyo., n Europe.
Variety compacta is distinctive and may be a good species, distinguished by its bright green color, small size, ovate concave leaves that often incurve when dry, and clear laminal cells.