rafflesia

rafflesia, (genus Rafflesia), genus of about 42 species of parasitic plants native to Southeast Asia. All Rafflesia species parasitize the roots of Tetrastigma vines (family Vitaceae), and their presence is not made known until the striking flowers emerge from the host vine. One species, Rafflesia arnoldii, boasts the largest single flower of any plant.

Physical description

Like other members of the family Rafflesiaceae, Rafflesia plants are endoparasitic, meaning that the vegetative organs are so reduced and modified that the plant body exists only as a network of threadlike cellular strands living almost wholly within the tissues of the host plant. There are no green photosynthetic tissues, leaves, roots, or stems in the generally accepted sense, although vestiges of leaves exist in some species as scales. Rafflesia plants are thus obligate parasites, which cannot live without the nutrition provided by the host. Despite the dramatic reduction of most of the plant body, the flowers are well developed and can be extremely large.

Rafflesia flowers are sturdy, typically with five substantial tepals (undifferentiated petals and sepals) surrounding the sex organs in a central cup. Interestingly, individual flowers are unisexual, meaning that pollination can occur only if another flower of the opposite sex is simultaneously blooming. The distinctive flowers are sapromyiophilous, meaning that they are pollinated by carrion-feeding flies, and they have a number of adaptations to attract their unconventional pollinators. Most are reddish or purplish brown and have a mottled pattern that resembles rotting flesh. In addition, they emit a fetid carrion odor during the few days they are blooming, and some species even generate heat to simulate decomposition. The unusual pollen is transferred by means of a sticky liquid that dries on the flies. The resultant fruit is a berry containing sticky seeds thought to be disseminated by fruit-eating rodents.

Major species and conservation

The genus includes the giant R. arnoldii, sometimes known as the corpse flower or monster flower, which produces the largest-known individual flower of any plant species in the world and is found in the forested mountains of Sumatra and Borneo. Its fully developed flower appears aboveground as a thick fleshy five-lobed structure weighing up to 11 kg (24 pounds) and measuring almost one meter (about one yard) across.

Most Rafflesia species are considered rare and, given their complete dependence on Tetrastigma vines, are extremely difficult to cultivate and very vulnerable to extinction. Major threats include the loss of rainforest habitat, due to logging and other land-use changes, and illegal harvest of the flowers for their purported medicinal properties. As of 2023 only one species, R. magnifica of the Philippines, has been formally evaluated, and it is listed as critically endangered by the IUCN Red List of Threatened Species, though scientists estimate that at least 60 percent of the species are endangered.