Cactus , Cactus or Cacti (Cactaceae ) are a family of flowering plants . These are almost all succulents or succulent plants , that is to say xeric plants that store their reserves in tissue " juice " to cope with long periods of drought . It should not be confused Cactus and succulent plant : all succulents are not cactus . These are families of plants that have adopted the same methods of struggle against drought , like Asclepiadaceae or Crassulaceae .