Plants commonly cemented to substrate. Stems with stalked mucilage hairs in leaf axils, stalks usually brown. Leaves spiraling around stem in several rows, usually brittle, commonly ending in a distinct apiculus of a single cell; costa sometimes poorly differentiated, sometimes not reaching the leaf insertion; laminal cells with thick longitudinal walls and often pitted or sinuose, transverse walls thin. Capsule 0.5-2 mm.
Species about 45 (11 in the flora): cosmopolitan.
Andreaea is easily recognized in the field by the dark green to blackish dense turf strongly adherent to a rock habitat, the brittle leaves, and capsule opening by four longitudinal lateral slits. These species are largely temperate montane to arctic-alpine in distribution, not uncommon on exposed acid rock surfaces. The present treatment follows B. M. Murray´s (1987, 1988, 1988b) detailed and thorough study closely except that Andreaea alpestris is treated as a synonym of A. rupestris and A. crassinervia as a synonym of A. rothii, following M. F. V. Corley et al. (1981), while infraspecific taxa are not recognized. The costa may be interpreted as strongly excurrent when it fills the leaf subula.