Plants: small, sometimes large, in tufts or loose cushions. Stems: erect (creeping in O. kellmanii), branches erect to ascending. Leaves: usually erect-appressed and straight when dry, spreading to wide-spreading when moist, ovate, oblong, lanceolate, ligulate, or linear-lanceolate, not rugose; margins entire or denticulate near apex; apex acute, acuminate, apiculate, or obtuse, awn absent (present in O. diaphanum); costa usually ending near apex; basal laminal cells elongate-linear or rectangular; distal cells usually rounded, almost isodiametric, 6–24 µm, papillose only over lumina, papillae 1–4 per cell, conic or 2-fid; marginal cells gradually shorter than basal. Sexual: condition gonioautoicous or cladautoicous, rarely dioicous; perichaetial leaves similar to stem leaves or sometimes slightly differentiated. Seta: to 6 mm. Capsule: immersed, emergent, or exserted, globose to cylindric, smooth or 8- or 16-ribbed, sometimes constricted below mouth when dry; stomata superficial or immersed; peristome double, rarely single or absent; exostome teeth 0, 8, or 16, papillose or striate; endostome segments 0, 8, or 16. Calyptra: mitrate, conic-oblong to short-conic, not split at base, smooth or papillose, ± hairy or naked, plicate (not or obscurely plicate in O. gymnostomum and O. obtusifolium), covering entire capsule. Spores: isosporous. Nearly worldwide, more common in temperate areas.

Species ca. 125 (47 in the flora).