Plants small, prostrate, usually freely branched, usually in mats. Stems smooth, radiculose, rhizoids smooth, in clusters contiguous to leaf insertion on abaxial side; axillary hairs minute, 2-3 cells in length, basal cell small, apical cell enlarged, ± clavate; paraphyllia none; pseudoparaphyllia minute, ovate, acute; epidermal layer ± bulging, outer cortical cells small, firm-walled in 1-2 layers, similar to epidermis, interior cortical cells somewhat uniform, enlarged, thin-walled; central strand absent. Leaves of stems and branches similar, usually imbricate, ± monomorphic and spirally arranged, or distinctly dimorphic and arranged in two dorsal and two ventral rows, erect or spreading and ± complanate when dry, spreading and often ± complanate when moist, bilaterally symmetric or asymmetric, lanceolate to ovate or elliptic, rounded, obtuse, or acute, acuminate to subulate, ecostate; margin elimbate, entire; laminal cells firm-walled, smooth or pluripapillose, distal cells quadrate (including rhombic) to hexagonal, oblate-hexagonal or rhomboidal, proximal cells oblate-oblong in several marginal rows, often elongate in mid-proximal region. Specialized asexual reproduction absent. Sexual condition autoicous; perigonia gemmiform, axillary; perichaetia terminal on short axillary branches, leaves erect, usually enlarged and sheathing sporophyte at maturity. Sporophytes usually numerous, solitary in perichaetia. Seta short to nearly absent, usually straight. Capsule immersed to shortly exserted, erect, radially symmetric, oblong- or ovoid-cylindric, pale yellow to yellow-brown; exothecial cells thin-walled, oblong to oblong-hexagonal, estomatose or stomatose, stomata superficial, restricted to base or proximal half of theca; annuli none to well developed; peristome none, or diplolepidous, composed of 16 papillose, lanceolate teeth, or reduced to irregular, pale, papillose segments; opercula conic-apiculate to conic-rostrate. Calyptra small, usually covering only opercula and distal ends of thecae, mitrate, lobed, smooth to ± papillose, more or less plicate, plicae often serrate or serrulate, or rarely, large, twisted, covering capsules completely and clasping the distal end of seta, or rarely, cucullate, ± papillose, non-plicate. Spores finely papillose to nearly smooth, relatively large. This family includes the genera Aulacopilum Wilson, Erpodium (Bridel) Bridel, Solmsiella Müller Hal., Venturiella Müller Hal., and Wildia (Müller Hal.) Brotherus. A sixth genus, Microtheciella Dixon, was transferred to the family Microtheciellaceae (H. A. Miller and A. J. Harrington 1977). Solmsiella is often combined with Erpodium (H. A. Crum 1972; A. Touw 1992; I. G. Stone 1997; D. M. Vital 1980). Stone also combined Aulacopilum, Venturiella, and Wildia with Erpodium, thus reducing the family to a single highly variable genus. Erpodium, Solmsiella, and Venturiella are recognized in North America.