Ptychomitrium linearifolium Reimers & Sakurai 1931

Ptychomitrium linearifolium is characterized by having leaves that are crisped when dry, tapered from an ovate base to long-linear toothed upper acumen. Sometimes, specimens of Ptychomitrium gardneri with long upper linear acumen can be misidentified as P. linearifolium. However, the former species differs by having more robust, multi-branched plants, and strongly plicate leaf bases.

Plants medium-sized, to 2–3 cm high, green to yellowish green above, brown to dark brown below, in loose tufts. Stems simple or sparsely branched; central strand well developed. Leaves 3.9–4.6 mm long, crisped or somewhat contorted when dry, erect-spreading to wide-spreading when moist, tapered from an ovate, more or less sheathing base to a long-linear and keeled upper acumen, acute at the apex; margins slightly recurved below, with large, remote teeth above, each tooth consisting of several cells; upper leaf cells obscure, rounded quadrate to subquadrate, 8–10 µm wide, with slightly thickened walls; basal cells elongate, 26–40 µm x 8–13 µm, hyaline, thin-walled. Autoicous. Perichaetial leaves similar to the upper stem leaves. Setae straight, yellow, 4–5 mm long; capsules erect, ellipsoid to oblong-ellipsoid, yellowish brown, 1.5–2.0 mm long; annuli undifferentiated; peristome teeth reddish brown, linear-lanceolate, bifid nearly to the base, sometimes perforate, finely papillose; opercula with a long, erect beak. Calyptrae mitrate, reaching the middle of the capsule, longitudinally plicate, lobed at the base. Spores spherical, finely papillose to nearly smooth.

Distribution: China, Korea, and Japan.

Habitat: on rocks and boulders, sometimes on thin soil over rocks in mountains.