Small annual or perennial herbs. Stems erect or prostrate (except in B. ruellioides). Leaves opposite, simple, sessile or petiolate, pinnately veined. Inflorescences terminal raceme, terminal and axillary racemes or clusters. Calyx deeply 5-lobed, calyx lobes. Corolla tubular, bilabiate; upper lip either entire or emarginated to shallowly 2-lobed, lower lip usually widely spreading 3-lobed, upper lip usually shorter than lower lip. Stamens 2 fertiles, 2 staminodes, didynamous; posterior stamens usually fertile and affixed to corolla tube, anterior stamens reduced to staminodes without spur or geniculum arising at or near the base; anthers free or contiguous, thecae divaricate. Ovary superior, ellipsoid, glabrous, bicarpelate with 2 locules, axial placenta with numerous ovules; style slender, erect; stigma bilamellate, flat. Fruits septicidal 2-valved capsules, cylindric. Seeds numerous, scrobiculate or reticulate, variously shaped.