Annual or perennial herbs, mostly woody at base, branches long, slender, mostly quadrangular. Leaves mostly linear or lanceolate, rarely ovate or obovate, upper leaves opposite, without stipules, lower in whorls, stipules filiform. Inflorescence a spike. Flowers small, generally solitary, sessile or shortly pedicellate; rose or blue, bisexual, tribracteate. Calyx minute, tube ± ovate, lobes inconspicuous. Corolla-tube longer than calyx-tube, 4-5 lobed. Stamens 4-5, included; anthers linear. Ovary ± compressed. Style bifid at apex, filiform, often longer than corolla-tube, branches unequal. Stigmas 2, globose. Fruit a 2-valved indehiscent capsule, oblong to oblong-linear, rarely subglobose. Seed 1, mostly oblong.