Annual or occasionally perennial, usually glabrous herbs, erect, spreading or cushion-like. Lvs opposite, sessile, sometimes amplexicaul. Fls in terminal dichasial cymes, arranged in corymbiform, capitate or spicate infls, (4)-5-merous. Calyx deeply lobed; lobes keeled, usually linear. Corolla salverform or ± funnelform, usually pink to purplish rose. Stamens usually inserted near apex or upper part of corolla tube; anthers linear or nearly so, twisting spirally after dehiscence. Style filiform, caducous; stigmas 2. Capsule fusiform to oblong-ovoid or ellipsoid; valve margins often intrusive. Seeds numerous, minute.