An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Rosidae of the class Magnoliopsida (dicotyledons). The order consists of three families and fewer than a hundred species, nearly all tropical or subtropical. The plants are highly specialized, nongreen, rootless parasites which grow from the roots of the host. They have few or solitary, rather large to very large flowers with numerous ovules and a single set of tepals that are commonly united into a conspicuous, corolloid calyx. Rafflesia is famous for its gigantic flowers, which in R. arnoldii of Sumatra are about 3 ft (1 m) in diameter. No other family has individual flowers even approaching this size.