Polytrichastrum sect. Meiotrichum G. L. Smith
Plants robust, polytrichoid. Stems simple to freely branched. Leaves with a sheathing base and divergent blade; sheath entire, hyaline margined; limb firm, serrate-toothed to the sheath, broadly lamellate on the adaxial surface; lamellae entire in profile, the marginal cells with the free wall thickened, the cuticle longitudinally striate and pitted. Capsule ventricose, 4--6-angled; hypophysis rugose, with conspicuous stomata; exothecial cells with rounded to slit-like thin spots in the external wall; operculum hemispherical, with a stout, hooked beak; peristome present, leiodont, teeth 64, simple. Calyptra sparsely hairy. Spores papillose.
Species 1: endemic to the mountains of western North America.
The one species was originally assigned to Polytrichadelphus, a genus of South America, southeast Asia, and Australia and New Zealand, because of the fastigiate habit and sparsely hairy calyptra. Characters found in all Polytrichadelphus species include margins of lamellae smooth, the marginal cells flask-shaped in section and crenulate in profile, capsule dorsiventral with two sharp angles, and multiple stomata dispersed over the exothecium.
Originally placed in Polytrichadelphus (a genus not present in our area) because of the fastigiate habit and sparsely hairy calyptra. All Polytrichadelphus species have lamellae which are crenulate in profile, the marginal cells smooth and flask-shaped in section, a dorsiventral capsule with two sharp angles, and multiple stomata dispersed over the exothecium, none of which occurs in Meiotrichum.
Smith, G. L. 1971. A conspectus of the genera of Polytrichaceae. Mem. New York Bot. Gard. 21(3): 1-83. fig. 1--128. Merrill, G. L. 1992. Notes on North American Polytrichaceae: Polytrichastrum G. Sm. Bryologist 95: 270--273.