Acanthaceae

Herbs or subshrubs, rarely small trees or climbers, sometimes mangroves, usually with cystoliths; branches often 4–6-angled or grooved, usually with transverse ridges across the nodes. Leaves opposite, simple, entire or shallowly toothed, rarely deeply incised; stipules absent. Inflorescence axillary or terminal spikes, cymes, racemes or clusters, or flowers solitary. Flowers usually zygomorphic, bisexual, often both chasmogamous and cleistogamous present on same plant, often subtended by a bract and with 2 leafy bracteoles; sepals usually 4 or 5, rarely more, equal and fused only at base or unequal and fused higher up; corolla tubular, regular or 2-lipped, with 5 spreading lobes; stamens fused with corolla, in 2 pairs of unequal length, 2 often sterile, filaments free or fused basally in pairs, anthers usually 2-celled, opening by longitudinal slits; ovary superior, 2-celled, ovules 2–12 per cell, style simple. Fruit a loculicidal 2-valved capsule, or, sometimes 1-celled by abortion, often opening explosively after drying or on wetting, usually with persistent seed-bearing hooks; seeds 2–many, compressed, discoid, sometimes with mucilaginous hairs, or solitary and viviparous in Avicennia.