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Rafflesia arnoldii flower and bud
Rafflesia arnoldii flower and bud
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Malpighiales
Family: Rafflesiaceae
Genus: Rafflesia

See text.

Rafflesia arnoldii flower and bud

Rafflesia is a genus of parasitic flowering plants. It was discovered in the Indonesian rain forest by an Indonesian guide working for Dr. Joseph Arnold in 1818, and named after Sir Thomas Stamford Raffles, the leader of the expedition. It contains 15-19 species (including four incompletely characterized species as recognized by Meijer 1997), all found in southeastern Asia, on the Malay Peninsula, Borneo, Sumatra and Kalimantan, West Malaysia, and the Philippines. The plant has no stems, leaves or true roots. It is an endoparasite of vines in the genus Tetrastigma (Vitaceae), spreading its root-like haustoria inside the tissue of the vine. The only part of the plant that can be seen outside the host vine is the five-petaled flower. In some species, such as Rafflesia arnoldii, the flower may be over 100 cm in diameter, and weigh up to 10 kg. Even the smallest species, R. manillana, has 20 cm diameter flowers. The flowers look and smell like rotting meat, hence its local names which translate to "corpse flower" or "meat flower" (but see below). The vile smell that the flower gives off attracts insects such as carrion flies, which transport pollen from male to female flowers. Little is known about seed dispersal, however, tree shrews and other forest mammals apparently eat the fruits and disperse the seeds. Rafflesia is an official state flower of Sabah in Malaysia, as well as for the Surat Thani Province, Thailand.

The name "corpse flower" applied to Rafflesia is confusing because this common name also refers to the Titan Arum (Amorphophallus titanum) of the family Araceae. Moreover, because Amorphophallus has the world's largest unbranched inflorescence, it is sometimes mistakenly credited as having the world's largest flower. Both Rafflesia and Amorphophallus are flowering plants, but they are still distantly related. Rafflesia arnoldii has the largest single flower of any flowering plant, at least when one judges this by weight. Amorphophallus titanum has the largest unbranched inflorescence, while the Talipot palm (Corypha umbraculifera) forms the largest branched inflorescence, containing thousands of flowers; this plant is monocarpic, meaning that individuals die after flowering.



Rafflesia arnoldii bloom, approximately 80 cm in diameter
R. kerrii flower
Three Rafflesia pricei growing in close proximity near Mount Kinabalu, Borneo.
New hypothesis of Rafflesiaceae derived from within Euphorbiaceae. Rafflesiaceae in red, Euphorbiaceae in black (redrawn from Davis et al., 2007).
Unverified species
  • Rafflesia borneensis
  • Rafflesia ciliata
  • Rafflesia irigaenses
  • Rafflesia titan
  • Rafflesia witkampii

Comparison of mitochondrial DNA (mtDNA) sequences of Rafflesia with other angiosperm mtDNA indicated that this parasite evolved from photosynthetic plants of the order Malpighiales.<ref> (January 20, 2004) "Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world's largest flower". PNAS 101 (3): 787-792. </ref>. Another study from that same year confirmed this result using both mtDNA and nuclear DNA sequences, and showed that three other groups traditionally classified in Rafflesiaceae were unrelated <ref> (October 20, 2004) "Phylogenetic inference in Rafflesiales: the influence of rate heterogeneity and horizontal gene transfer". BMC Evolutionary Biology 4: 40. </ref>. A more recent study found Rafflesia and its relatives to be embedded within the family Euphorbiaceae, which is surprising as members of that family typically have very small flowers.<ref> (January 11, 2007) "Floral gigantism in Rafflesiaceae". Science doi: 10.1126/science.1135260. </ref> According to their analysis, the rate of flower size evolution was more or less constant throughout the family except at the origin of Rafflesiaceae, where the flowers rapidly evolved to become much larger before reverting to the slower rate of change.