Description: Annual or [perennial herbs, vines or shrubs]; glabrous or pubescent with glandular or non-glandular hairs.
Leaves opposite or sometimes whorled, rarely alternate, simple and margins entire, toothed or lobed or pinnately compound; petiolate or sessile, not or scarcely ridged across nodes.
Flowers solitary, axillary, or forming irregular terminal racemes or panicles; bracteoles absent. Sepals 4, fused only at base, slightly unequal. Corolla strongly 2-lipped, upper lip 2-lobed, truncately rounded, entire and sometimes hooded; lower lip 3-lobed, often large and inflated, concave and slipper-shaped. Stamens 2, of 2 distinct kinds, either anther loculi contiguous and both loculi fertile or loculi separated on connective and both loculi fertile or 1 modified and fertile, sterile or absent. Style short.
Capsule septicidal, secondarily scarcely loculicidal apically, 4-valved; seeds numerous, minute.
Distribution and occurrence: World: c. 500–600 species, Mexico to South America. Australia: 1 species (naturalized).
Text by W. R. Barker