Leaves ovate to short-elliptic, apex broadly acute, awned, margins recurved in mid 4/5 of leaf, usually bordered distally with 2-4 rows of smooth or less papillose, some-what thicker-walled cells; costa excurrent in the awn, lacking an adaxial pad of cells, distally narrow, 2-4 cells across the convex adaxial surface; distal laminal cells hexagonal, 16-19 µm wide, 1:1, papillose with 4-6 1- to 2-fid papillae. Sexual condition autoicous. Sporophytes exerted. Seta 0.7-0.8 cm. Capsule stegocarpic, not systylius, cylindric, erect and nearly straight, urn 1.2-1.4 mm; peristome ca. 500 µm, of 16 teeth, weakly twisted, divided to below the middle, basal membrane to 75 µm high; operculum ca. 0.8 mm. Spores 13-18 µm, spheric, papillose.
Tortula guepinii resembles T. hoppeana of montane and subarctic distribution in North America and elsewhere, but it is smaller, with leaves less than 2 mm, and cells of the leaf margin are distinctly less papillose at the apex. Tortula plinthobia of the southeastern and southwestern United States has distal laminal cells only 10-13 µm wide.