1. Amphidium Schimp., Coroll. Bryol. Eur. 39. 1856.
Plants slender, dull to dark green or yellowish brown, in dense cushions. Stems erect, simple or branched, radiculose below. Leaves crowded, crispate or contorted when dry, erect-spreading when moist, keeled, linear to narrowly oblong-lanceolate, acuminate at the apex; margins slightly recurved below the middle; costa single, strong, ending near the apex; upper cells small, rounded-quadrate to rounded-hexagonal, thick-walled, not transparent, pluripapillose; lower cells rectangular, thin-walled, hyaline, smooth. Dioicous or autoicous. Perichaetial leaves large, completely sheathing at base. Setae short, straight; capsules emergent or slightly exserted, erect, symmetric, oblong-cylindric from a broad, tapered neck, distinctly 8-ribbed and reddish brown when dry; opercula apiculate or rostrate with an oblique beak; annuli and peristome none; stomata present in the neck, superficial. Calyptrae cucullate, smooth. Spores small, spherical, smooth or nearly so.
The genus Amphidium consists of about 11 species in the world. Most species are found growing on an acid substratum. Three species and one variety were reported from China (Redfearn et al. 1996); however, only one species, Amphidium lapponicum (Hedw.) Schimp., is treated in this study. Amphidium sublapponicum (C. Muell.) Broth. was synonymized with A. lapponicum by C. Gao (1994) and A. mougeotii (Bruch & Schimp.) Schimp. var. formosicum Card. with Hymenostylium recurvirostre (Hedw.) Dix. by C.-M. Kuo and T.-Y. Chiang (1987). Redfearn et al. (1996) mistakenly listed A. mougeotii from Taiwan based on a citation of P.-C. Chen et al. (1963). In addition, we cannot verify A. papillosum Bartr. reported from Taiwan (C.-K. Wang 1969).
Amphidium is similar not only to Rhabdoweisia, but also to Zygodon and Orthotrichum of the Orthotrichaceae. Amphidium has been placed in the latter family by several recent treatments (Crum & Anderson 1981; Lewinsky 1976), indicating that the genus is closely related to diplolepideous genera rather than to such halpolepideous genera as Rhabdoweisia. In this study we still place Amphidium in the family Dicranaceae, because of the tradition of treating the genus in the Chinese moss flora.