1 (also crown-of-thorns-starfish) a large spiky starfish of the tropical Indo-Pacific, feeding on coral and sometimes causing great damage to reefs.
- Acanthaster planci, class Asteroidea
2a Madagascan shrub of the spurge family, with bright red flowers and many slender thorns. It is a popular houseplant and is sometimes used for hedges in the tropics.
- Euphorbia milii, family Euphorbiaceae
any of a number of other thorny plants, especially Christ’s thorn.