Tortula leucostoma

Leaves ovate-lanceolate or occasionally ovate, apex broadly acute or rounded-acute, piliferous, margins recurved in middle ²/3 of leaf or more, not or weakly bordered distally with ca. 2 rows of less papillose, thicker-walled cells, to ca. 2:1; costa long-excurrent, lacking an adaxial pad of cells, distally narrow, 2-3 cells across the convex adaxial surface; distal laminal cells hexagonal, 13-20 µm wide, 1:1, densely papillose with several 2-fid papillae. Sexual condition autoicous or paroicous. Sporophytes exerted. Seta 0.4-1.9 cm. Capsule stegocarpic, short-cylindric, erect and nearly straight, urn 1.5-2 mm; peristome 300-500 length µm, teeth 16, divided to near the base or perforate basally, the teeth often basally fused into a low basal membrane ca. 50 µm; operculum 0.5-0.6 mm. Spores ca. 23-25 µm, spheric, densely papillose.

Capsules mature summer. Soil, silt, clay, especially calcareous substrates, occasionally runways and burrows of small mammals, typically subarctic, Arctic and alpine habitats; low to high elevations (0-3700 m); Greenland; B.C., Nfld. and Labr., N.W.T., Nunavut, Yukon; Alaska, Ariz., Calif., Colo., Mont., Wash.; Europe; Asia.

Tortula leucostoma and T. guepinii were considered by W. C. Steere (1939c) to be probably subspecies of T. hoppeana (as Desmatodon latifolius). This species differs from T. hoppeana largely by the tapering leaf with piliferous costa, and perhaps the somewhat shorter seta.