Rafflesia

Replica Rafflesia displayed in Philippine National Museum

The plant has no stems, leaves or roots. It is a holoparasite of vines in the genus Tetrastigma (a plant in the Vitaceae, the grape vine family), spreading its absorptive organ, the haustorium, inside the tissue of the vine.[6] The only part of the plant that can be seen outside the host vine is the five-petalled flower. In some species, such as Rafflesia arnoldii, the flower may be over 100 centimetres (40 in) in diameter, and weigh up to 10 kilograms (22 lb). A Rafflesia that flowered in West Sumatra in 2019 was measured to be almost 4 feet (120 cm) in diameter, the largest flower ever recorded – 4 inches (10 cm) wider than the flower reported as the largest in 2017.[7] Even one of the smallest species, R. baletei, has 12 cm (5 in) diameter flowers.

The flowers look and smell like rotting flesh. The foul odour attracts insects such as carrion flies, which transport pollen from male to female flowers. Most species are dioecious, having separate male and female flowers, but a few (R. baletei and R. verrucosa) have hermaphroditic flowers.[8] Little is known about seed dispersal. Tree shrews and other forest mammals eat the fruits.[9] The extremely tiny seeds have extremely tiny elaiosomes, and are thus most likely dispersed by ants. The seeds are packed into berries, which contains hundreds of thousands of seeds.[6]

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 unrelated to each other. Rafflesia arnoldii has the largest single flower of any flowering plant, at least in terms of weight. Amorphophallus titanum has the largest unbranched inflorescence, while the talipot palm (Corypha umbraculifera) forms the largest branched inflorescence, containing thousands of flowers; the talipot is monocarpic, meaning the individual plants die after flowering.

Rafflesia are also remarkable for showing a large horizontal transfer of genes from their host plants. This is well known among bacteria, but not higher organisms. It occurs in the mitochondria (originally derived from bacteria) found within the cells of Rafflesia; these appear to have exchanged genes with the mitochondria of the host tissue.[6][10]

In Indonesian it is known as padma. R. arnoldii is known as padma raksasa ("giant padma").[11] In Javanese it is called patma.[12] In Malay, the 'normal' R. hasseltii is vernacularly known as pakma, patma or ambai-ambai,[4][12][13] whereas the goliath R. arnoldii from Sumatra is called krubut or kerubut, 'great flower'.[4][13] The words padma, pakma or patma originate etymologically from the word पद्म (padma), Sanskrit for 'lotus'.[13]

A webpage for a class project by two American students, made in 2003, incorrectly stated that the local name translated to "corpse flower".[14] A month later this sentence was copied to Wikipedia,[15] but due to subsequent edits, by 2010 the sentence came to claim that the English name was "corpse flower",[16] and by 2020 this name has been used numerous times in news articles and the like.

The name "corpse flower" referred to the titan arum (Amorphophallus titanum) of the family Araceae.[6]

According to a CNN reporter, the flower has been called the "monster flower".[7]

Robert Brown introduced the genus Rafflesia to the wider scientific world in a presentation before the Linnean Society of London in June 1820, but his scientific paper on the subject was only published in late 1821.[1]

In 1999 the British botanical historian David Mabberley pointed out that the genus Rafflesia was first validated by an anonymous report on the meeting published in the Annals of Philosophy in September 1820 (the name was technically an unpublished nomen nudum until this publication). Mabberley claimed the author was Samuel Frederick Gray.[17] However, as that is nowhere stated in the Annals, per Article 46.8 of the code of ICBN, Mabberley was wrong to formally ascribe the validation to Gray. The validation of the name was thus attributed to one Thomas Thomson, the editor of the Annals in 1820, by the IPNI. Mabberley admitted his error in 2017.[1] This Thomson was not the botanist Thomas Thomson, who was three years old in 1820, but his identically named father, a chemist.[18]

Rafflesia keithii bloom, approximately 80 cm in diameter near Taman Nasional Rafflesia Bengkulu, Indonesia

Rafflesia kerrii flower near Langkat, Indonesia

Three Rafflesia pricei growing in close proximity near Mount Kinabalu, Borneo

Comparison of mitochondrial DNA (mtDNA) sequences of Rafflesia with other angiosperm mtDNA indicated this parasite evolved from photosynthetic plants of the order Malpighiales.[19] Another 2004 study confirmed this result using both mtDNA and nuclear DNA sequences, and showed the three other groups traditionally classified in Rafflesiaceae were unrelated.[20] A 2007 study more specifically found Rafflesia and its relatives to be embedded within the family Euphorbiaceae as traditionally circumscribed, which was surprising, as members of that family typically have very small flowers. 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.[21]

To maintain monophyletic families, in 2016 the APG IV system separated the family Peraceae from the Euphorbiaceae.[22] A summary cladogram is shown below,[21] with family placements in the APG IV system.[22]

A 2010 molecular phylogenetic study of 18 species of Rafflesia found that they fell into four clear-cut geographically defined groups:[23]

However, the clear monophyly of the four geographical clades does not correspond to any clear difference in appearance. There is no consistency within the clades in the size of flowers, or the presence or absence of white warts; species in different clades resemble one another more than they do some other species within the same clade. Homoplasy – repeatedly gaining or losing traits – seems to be the rule within Rafflesia.[23]

Rafflesia arnoldii life cycle.

Species of Rafflesia are all thought to be holoparasites of lianas of the genus Tetrastigma, vines which belong to the Vitaceae, the family of the grape vines. They are thus, in a way, hyperparasites, because Tetrastigma are themselves, in a way, structural parasites of the trees they use to climb up to the light. Rafflesia appear to be species-specific, with each Rafflesia species naturally only growing on one to three species of Tetrastigma. Of the 57 known species of Tetrastigma, only ten are known to be host plants. Of the 30 odd species of Rafflesia, the host plants are only known from about half of the species. A certain species of Tetrastigma is very popular among Rafflesia: T. tuberculatum is a host plant for at least 15 species, and only two Philippine species are not known to infect it. T. papillosum and T. diepenhorstii both host at least two species. The flowers may bud from different locations; R. cantleyi flowers from the vine some two meters from the ground, [41] whereas R. zollingeriana always buds out of the roots and appears out of the ground.[42]

The gender ratio may be skewed. In R. lobata there are approximately nine male flowers for every female flower.[43] Rarely are there flowers of both sexes at one location to ensure pollination and thus sexual reproduction. This may not matter: female flowers usually form fruit anyway and may thus be agamospermous.[41] Flowering is relatively constant, and sites may continue to flower for decades.[44][45]

In Rafflesia arnoldii the flowers are visited by the flies Drosophila colorata, Chrysomya megacephala and Sarcophaga haemorrhoidalis. Black ants of the genus Euprenolepis may feed on the developing flower buds, perhaps killing them.[46] Mammals which are known to eat the flowers are the Javan treeshrew Tupaia javanica and the porcupine Hystrix javanica. Mammals which have been recorded destroying the buds or flowers, often simply by stepping on and crushing them, are: pigs (Sus scrofa), wild cats (Felis bengalensis), rusa (Cervus timorensis), muntjak (Muntiacus muntjak) and banteng (Bos javanicus).[41]

In Thailand the buds and flowers of R. kerrii are considered a delicacy. They are also harvested for herbalism, a concoction is believed to act as a sexual stimulant and to help for fever or backache.[47] In the Philippines the plants are also used in folk herbalism, but the flowers are also fed to swine as fodder.[45] On Java the buds of R. zollingeriana are harvested and dried for use in jamu, the ancient traditional herbalism of the island. It is unknown for what the buds are supposed to be good for;[44] jamu concoctions are often complex mixtures and often are supposed to help with sexual prowess.

These plants also have some economic use in attracting ecotourists.[48]

Research in Malaysia and Indonesia has made it possible to propagate the species for use in horticulture, with the famous Bogor Botanical Garden growing the first plants in the 1850s using grafts of infected vines. The Malaysian biologist Jamili Nais was the first to propagate the plants using the seeds around the year 2000.[41]

• Amorphophallus titanum, a similar smelling plant, sometimes known as the "corpse flower"
• Parasitic plant
• Carrion flower

• Sofiyanti, Nery; Yen, Choong (December 2012). "Morphology of Ovule, Seed, and Pollen Grain of Rafflesia R. Br. (Rafflesiaceae)". Bangladesh Journal of Plant Taxonomy. 19 (2): 109–117. doi:10.3329/bjpt.v19i2.13124.

• Media related to Rafflesia at Wikimedia Commons
• Rafflesia flower and threats
• Parasitic Plant Connection: Rafflesia Gallery
• ARKive: images and movies of the rafflesia (Rafflesia spp)