Herbs or shrubs, rarely climbers (Thunbergia). Leaves opposite, decussate, simple, without stipules; cystoliths commonly present on leaves and other vegetative parts, appearing as white streaks. Flowers usually in cymes, racemes or spikes but sometimes solitary or in axillary whorls, bisexual, often zygomorphic. Bracts and usually bracteoles present, bracts often prominent and concealing calyx, sometimes arranged in 3-4 levels especially in those genera with axillary inflorescences. Calyx 4-5 lobed, lobes usually similar in genera with 5 lobes but often dissimilar in those with 4 lobes such as Barleria; much reduced in Thunbergia. Corolla usually 5-lobed but often 2-lipped with lower lip 3-lobed and upper lip notched or (in Acanthus) absent. Stamens attached to corolla, usually 4 in two dissimilar pairs, sometimes 2 with second pair reduced to staminodes; anthers 1-2-celled, sometimes spurred at base, cells at same level or one below the other; pollen very varied in appearance and often distinctive for a particular genus. Ovary superior, 2-celled; ovules 2-numerous. Style 1; stigma 2-lobed, posterior lobe often reduced and apparently absent. Fruit a loculicidal capsule, usually cylindrical or clavate in shale (globose and beaked in Thunbergia); seeds usually borne on short hook-like retiacula which eject the seed when ripe capsule opens. seeds usually flattened, lens-shaped, glabrous or hairy, sometimes with elastic mucilagenous.A tropical family well represented in the warm subtropical valleys and foothills. Most species flower in the dry winter season.
Small shrubs. Leaves petiolate, entire, usually dark shiny green and above and noticeably paler beneath. Flowers in small cymes, sometimes axillary but usually arranged in a dense raceme-like panicle, known as a thyrse. Bracts small, inconspicuous; bracteoles 0. Calyx deeply 5-lobed, segments very narrow. Corolla tubular, curved, shortly 2-lipped. Stamens 2; anthers 2-celled, cells oblong, muticous. Ovary glabrous. Capsule elongate, many-seeded from base; seeds lens-shaped, glabrous or hairy.
Shrub up to 3m. Stems erect, glabrous. Leaves often crowded near branch tips, elliptic(-obovate), 11-28 x 2.5-8cm, shortly acuminate at both ends, glabrous; petiole 15-35mm. Flowers in a dense, uninterrupted terminal thyrse, 4-23 x 4-5cm, usually solitary, rarely 2-3; rhachis pubescent. Bracts linear, c 10mm, pubescent. Calyx c 6mm, pubescent, lobes linear. Corolla orange-brown, tubular, 20-25mm, c 8mm wide at mouth, pubescent; upper lip 6-7mm, spreading, about twice as long as deflexed lower lip. Anthers 4-5mm, shortly exserted. Capsule narrowly clavate, 2-3cm.