Annual or perennial herbs, or small shrubs; stems erect to prostrate or 0, rarely lianoid. Lvs usually opposite, sometimes whorled, entire, toothed to pinnate, pinnately or palmately veined. Fls usually in terminal or, less often, lateral cymes, sometimes in dichasia, or solitary and axillary. Calyx deeply 4-lobed, sometimes lobes only fused near base. Corolla very irregular, usually yellow; upper lip small, ± ascending, pouched; lower lip > upper; pouch very inflated, ± slipper-like and consisting of the whole lip (really composed of 3 lobes). Stamens 2, included; anther cells contiguous and both fertile, or cells separated by a connective and either both fertile or one sterile or 0. Capsule septicidal, splitting at apex. Seeds numerous, ± tuberculate, not winged.