Annual or perennial erect herb. Stem quadrangular, generally much branched from the base. Leaves opposite, linear-lanceolate, rarely narrowly ovate, membranous or flat, sometimes thickened and revolute; midrib distinct beneath. Inflorescence a sparingly much branched cyme; bract and bracteoles foliaceous much smaller than vegetative leaves. Flowers white, rose or lilac, 3-6 mm long, glabrous or hirsute, pedicels 1-5 mm long. Corolla-tube 1.5-4.5 mm long, usually 1.5-3 times longer than the lobes, lobes narrowly triangular. Anthers inserted at the mouth of corolla tube. Style 1-3 mm long, included, bifid, branches ± equal; stigmas 2, globose. Mericarps glabrous, puberulous or hirsute, oblong.