crown of thorns

noun

• 1a 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 hedging in the tropics. Also called Christ's thorn.

  • Euphorbia milii, family Euphorbiaceae
• any of a number of thorny plants, especially Christ’s thorn (Ziziphus spina-christi).