Any of the more than 2,500 plant species that make up the family Acanthaceae, of the figwort order.
Acanthus are found mostly in tropical and subtropical regions. Most are herbaceous plants or shrubs that grow in tropical rainforests; some are climbers (vines) or trees. Acanthus have simple leaves arranged in opposite pairs on the twigs and enlarged cells called cystoliths in streaks or protuberances in the vegetative parts. The bisexual flowers are bilaterally symmetrical and usually crowded together in clusters. Individual flowers are enclosed by leaflike bracts, which are often coloured and large. Acanthus are mainly of horticultural interest and include some ornamentals.