Perennial herbs or undershrubs, erect, trailing or ascending, branched or not, glabrous to scabrid or strigose. Leaves opposite. Inflorescence terminal, racemose; flowers solitary, axillary, bracteate, pedicellate or not, 2-bracteolate. Calyx tubular to campanulate, 5-lobed; lobes valvate, ± equal. Corolla tube short, expanding and inflated above; limb oblique, 2-lipped; the lower lip overlapping the upper in bud, 3-lobed; the upper lip obovate, shortly bilobed. Stamens 4, didynamous, included, upper pair of anthers without appendage, lower pair with connective, the upper branch of which bearing one anther, the lower curving upwards and ending in a rounded appendage; anthers monothecal, dehiscing by an apical pore. Ovary 2-locular. Capsule 2-valved. Seeds numerous, angular, pitted.