Perennial or sometimes annual or biennial herbs. Stems erect or ascending, branched, glabrous. Leaves opposite, succulent, sessile or petiolate, lamina undivided or rarely pinnatifid, entire, crenate or serrate, usually flat or sometimes semiterete, glabrous. Inflorescence terminal or axillary, panicle or corymb-like, sometimes thyrsoid, composed of cymes. Flowers 4-merous, pedicellate, erect, bisexual, large, brightly coloured. Sepals free or more or less connate, shorter than or sometimes equalling the corolla-tube. Corolla gamopetalous, tubular, lobes 4. Stamens 8, in two whorls, adnate to the corolla-tube, anther dithecous. Carpels 4, free or slightly connate at the base, styles usually shorter than the ovaries, stigma capitate. Nectar scales semi-orbicular to linear, entire, crenulate or emarginate at the top. Follicles 4, many-seeded. Seeds oblong or ellipsoid, with lontitudinally rugose tegument.