Erect to decumbent, perennial herbs with opposite to sub-opposite, simple, exstipulate leaves. Inflorescence spicate, terminal or axillary. Flowers small, bracteate, usually white or bluish. Calyx tube 5-ribbed, minutely 4-5-toothed, persistent, enlarged and often ovoid inflated in fruit. Corolla-tube straight to subcurved, about as long or slightly exceeding the calyx; limb 5-lobed, somewhat 2-lipped, oblique; axial lip 2, short lobed, abaxial 3-lobed, larger with the middle lobe largest. Stamens 4, didynamous, ± included, inserted at the middle or a little above the middle of corolla-tube, dithecous with connectives thickened or sagittate; fifth stamen, if present, reduced to a minute staminode. Ovary 2(-4)-loculed with each locule 2 or 1-ovuled; style linear, included. Fruit dry, usually hard schizocarp of 2 cocci separating easily at maturity, suborbicular; seeds exalbuminous.