Annual or perennial herbs or subshrubs. Stems 4-angled. Leaves opposite or sometimes in whorls of 3. Flowers bracteate, terminal, in simple spikes or panicles of spikes. Calyx tubular, distinctly and ± unequally (4-)5-toothed, 5-ribbed. Corolla funnel- or salver-shaped; limb 5-lobed, ± spreading. Stamens (2-)4(-5), included, didynamous. Ovary entire or 4-lobed, 4-locular with 1 ovule per loculus. Fruit splitting into 4 nutlets at maturity, enveloped in the persistent calyx.