Plants: small, in dense cushions. Stems: erect, branches ascending. Leaves: twisted and contorted when dry, spreading when moist, linear to narrowly lanceolate, not rugose; margins entire or toothed; apex acute; costa percurrent or short-excurrent; basal laminal cells rectangular; distal cells rounded, 5–11 µm, papillose over lumina and transverse walls, papillae cuticular; marginal cells not much different from basal. Sexual: condition autoicous or dioicous; perichaetial leaves larger than stem leaves. Seta: 1–3.5 mm. Capsule: mostly emergent to immersed, oblong, 8-ribbed, constricted below mouth; stomata superficial; peristome absent. Calyptra: cucullate, smooth, naked, not plicate, covering 1/2 capsule. Spores: isosporous. North America, Mexico, Central America, South America, Europe, Asia, Africa, Pacific Islands, Australia.

Species 12 (3 in the flora). Amphidium forms limey green cushions in seepages of non-calcareous rock. The basal laminal cells are smooth. The absence of peristome has led to considerable discussion of the placement of the genus. J. Lewinsky (1976) suggested placement in Orthotrichaceae, while D. H. Vitt (1973) proposed Rhabdoweisiaceae Limpricht. Although Amphidium is treated here in Orthotrichaceae, recent DNA evidence indicates closer relationships with Haplolepideae [unranked] (B. Goffinet et al. 1998) and Rhabdoweisiaceae (M. Stech 1999b).