Ptychomitrium formosicum Brotherus & A. Yasuda 1928

Ptychomitrium formosicum is distinguished by having median and basal juxtacostal cells with sinuose walls, annuli well developed, and leaves crisped when dry (Brotherus 1928). It is similar to P. tortula in having sinuose median and basal juxtacostal cells, but it differs by having smaller plants (2–6 cm vs. 9–15 cm), leaves crisped, but not strongly contorted when dry and straight, but not secund when moist, less strongly sinuose leaf cells, and by having well-developed annuli.

Plants medium-sized to large, slender, to 2–6 cm high, yellowish green above, dark green to reddish brown below, in loose tufts. Stems branched; central strand well developed. Leaves 5.0–5.5 mm long, crisped when dry, spreading when moist, linear-lanceolate from an oblong, plicate base, keeled above, acute or acuminate at the apex; margins revolute on one side below, strongly and remotely toothed above, each tooth consisting of several cells; costa single, strong, percurrent; upper leaf cells irregularly subquadrate, 5–8 µm wide, with slightly thickened walls; median cells short-rectangular, 10–15 µm x 5–7 µm, with sinuose walls; basal cells near margins short-rectangular to oblong-rectangular, 15–26 µm x 8–10 µm, with thin, straight walls; basal juxtacostal cells elongate to linear-elongate, 30–40 µm x 4–5 µm, with sinuose walls. Autoicous. Perichaetial leaves similar to upper stem leaves. Setae elongate, (8–)10–15 mm long, straight, yellowish brown, twisted above; capsule erect, oblong-ellipsoid, yellowish brown, 1.3–1.5 mm long; annuli well developed, consisting of two rows of thick-walled cells; peristome teeth reddish brown, linear-lanceolate, forked nearly to the base, densely and finely papillose; opercula with a long, erect beak. Calyptrae mitrate, reaching to the middle of capsules, longitudinally plicate, lobed at the base. Spores small, spherical, 8–10 µm in diameter, finely papillose.

Distribution: China (Taiwan) and Japan.

Habitat: on rocks at high elevations, 2500–3500 m.