Amphidium Schimper, Coroll. Bryol. Eur. 39. 1856.
[a variant of Amphoridium (nomenclaturally unavailable) and means like an urn, referring to the capsule shape].
Dale H. Vitt
Plants small, in dense cushions. Stem leaves twisted and contorted when dry, linear to narrowly lanceolate, acute; margins entire or toothed above, costa strong; distal laminal cells small, rounded, obscured by numerous, elliptic cuticular papillae over lumens and transverse walls; basal cells yellow-clear, smooth. Sexual condition autoicous or dioicous. Perichaetial leaves larger and ± clasping seta; gemmae not produced. Seta short 1.0--3.5 mm. Capsule oblong, 8-ribbed, constricted below mouth, mostly emergent to immersed; peristome none; stomates superficial. Calyptra cucullate, naked, smooth. Spores isomorphic.
Species 12 (3 species in the flora); North America, Europe, Asia, Africa, Pacific Islands, Australia.
Limey green cushion-forming plants in seepages of non-calcareous rocks is descriptive and diagnostic for all species. The lack of a peristome has lead to considerable discussion of the placement of the genus. J. Lewinsky (1976) suggested correct placement in the Orthotrichaceae while D. H. Vitt (1973) proposed the Rhabdoweisiaceae. Although treated here in the former family, recent DNA evidence indicates closer relationships with the Haplolepideae (Goffinet et al. 1998) and the latter family (Stech 1999).
Goffinet, B., R. J. Bayer, and D. H. Vitt. 1998. Circumscription and phylogeny of the Orthotrichales (Bryopsida) inferred from rbcL sequence analyses. Amer. J. Bot. 85: 1324--1337. Stech, M. 1999. A molecular systematic contribution to the position of Amphidium Schimp. (Rhabdoweisiaceae, Bryopsida). Nova Hedwigia 68: 291--300.