1. Amphidium Schimper, Coroll. Bryol. Eur. 39. 1856. • [Variant of.
Amphoridium (nomenclaturally unavailable), diminutive of Greek amphora, flask, alluding to capsule shape]
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.
Species 12 (3 in the flora): North America, Mexico, Central America, South America, Europe, Asia, Africa, Pacific Islands, Australia.
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).
SELECTED REFERENCE Stech, M. 1999b. A molecular systematic contribution to the position of Amphidium Schimp. (Rhabdoweisiaceae, Bryopsida). Nova Hedwigia 68: 291-300.