Stamens 4, didynamous, inserted in mouth of corolla tube, filaments of anterior pair usually bent round posterior pair at base; anthers usually cohering in parts, thecae confluent.
Corolla bilabiate; tube short, produced at front into sac or spur; posterior lip 4-lobed, anterior lip entire or emarginate with palate at base.
Flowers in terminal racemes at end of branches or solitary-axillary, bracteate, pedicellate, bracteoles absent.
Seeds numerous in one or two series, cylindrical-ellipsoid with entire or interrupted membranous wing.
Capsule laterally compressed, septicidal.
Annual or perennial herbs or undershrubs.
Leaves opposite, entire or toothed.
Ovary bilocular, ovules numerous.
Style filiform.
Calyx 5-lobed.