Plants reddish to black. Leaves erect-spreading, straight or sometimes secund, lanceolate, widest proximally, apex symmetric; costa absent; leaf margins entire; basal laminal cells rectangular to long-rectangular, marginal cells quadrate, walls little pitted; medial laminal cells rounded-quadrate to ovate, 1-stratose entirely or sometimes 2-stratose in patches distally, lumens rounded; laminal papillae rare, low. Sexual condition cladautoicous; perichaetial leaves differentiated, convolute-sheathing. Spores 12-20(-30) µm.
2. Andreaea mutabilis Hook.f. & Wils., 多态黑藓 duo-tai hei xian London J. Bot. 3: 536. 1844. Type. New Zealand, Auckland Island, J. D. Hooker 50 (lectotype BM); Campbell Island, J. D. Hooker Ib. (syntype BM). Andreaea hohuanensis Chuang, J. Hattori Bot. Lab. 37: 427. 1973. Type. China: Taiwan, C.-C. Chuang 5914 (holotype UBC). Synonymized by Murray (1988).
Plants small, slender, ca. 1 cm high, purple-red to black, in dense tufts. Stems rigid, erect, moderately branched. Leaves 0.60–0.75 mm × 0.1–0.2 mm, erect to erect-spreading when dry, often distant, sometimes falcate-secund, lanceolate, with long acuminate to acute apex; the lower leaves small, with broader base and shortly acute apex; margins entire, more or less incurved; upper and median laminal cells irregularly round to oval, 4–8 µm × 3–6 µm, thick-walled, papillose; basal cells near margins isodiametric to oblate, 4–8 µm × 8–10 µm; central basal cells elongate, 20–30 µm × 4–5 µm, irregularly thick-walled, pitted. Autoicous. Perichaetial leaves oblong-lingulate, acuminate, about 1 mm long. Pseudopodium ca. 1 mm long. Capsules oblong-ovate, dark brown, 0.5–0.6 mm long, split from near base to apex into 4 valves when mature. Spores 14–18(–20) µm in diameter, finely papillose.