5. Ptychomitrium linearifolium Reim. in Reim. & Sak. 狭叶缩叶藓 xia-ye suo-ye xian
Bot. Jahrb. 64: 539. 1931. Type. Japan: Mar. 1879. F. Schaal s.n.
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 × 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.