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Biology

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The enormous Rafflesia flowers are believed to be pollinated by flies; alighting on the central disk flies crawl underneath it where they come into contact with the sexual organs (2). It has been reported that the flowers have a strong smell of rotting flesh but it is unclear whether this acts to attract flies or is merely a by-product of the decaying petals, which reduce into a black slimy mess after around 4 days (2).
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Conservation

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Rafflesia species are protected in a number of reserves within their range such as Mount Kinabalu National Park in Sabah on the island of Borneo (5). Habitat protection is one of the key factors in securing the future of this species and this magnificent flower is a huge draw to tourists, bringing much needed revenue to the area. More investigation into the life cycle of this unusual species is urgently needed to enable propagation and ex-situ conservation measures (3). Recent success in propagating R. keithii is an encouraging step forward in the preservation for future generations of one of the world's most astonishing plant species (4).
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Description

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The dramatic Rafflesia flowers are the largest single flowers in the world; the leathery petals can reach over 90 centimetres across (2). Rafflesia is a parasite that depends completely upon its host; the majority of the plant's tissues exist as thread-like strands entirely within the host's cells (3). These host plants are vines of Tetrastigma spp., and the Rafflesia plant is itself not visible until the reproduction stage when flowers first bud through the woody vine and then open into the magnificent spectacle that is world-renowned today (4). The flowers can take up to 10 months to develop from the first visible bud to the open bloom, which may last no more than a few days (5). Currently 17 species of Rafflesia are recognised and these mainly differ in the morphology of their flowers (4). In general however, the flowers consist of 5 leathery petals that are orange in colour and mottled with cream-coloured warts (2). There is a deep well in the centre of the flower containing a central raised disc raised that supports many vertical spines (2). The sexual organs are located beneath the rim of the disk, and male and female flowers are separate (2).
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Habitat

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Rafflesia plants are specialist parasites only found in association with specific species of the host vine Tetrastigma spp. These vines are found in both primary and secondary rainforest (4).
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Range

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Species of Rafflesia are known from peninsular Malaysia, Sumatra, Java, southern Thailand, Borneo and southern Philippines (4). The genus as a whole is considered to be rare although information on distribution is lacking due to the difficulties of identifying plants within their host vines (4).
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Status

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Rafflesia manillana is classified as Endangered on the 1997 IUCN Red List of Threatened Plants (1). R. keithii and R. pricei are classified as Vulnerable; R. cantleyi, R. kerrii and R. zollingeriana are classified as Rare (1); R. hasseltii is classified as Indeterminate (1).
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Threats

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Rafflesia are inherently rare as a result of a number of factors of their life cycle; they have a double habitat specialisation, as they can only successfully parasitise particular species and these species in turn are found only in specific habitats (4). In addition to this factor, there is an extremely unbalanced sex ratio in the Rafflesia flowers observed, with many more male than female flowers (4). Flower buds have a high level of mortality and only 10-18% go on to bloom, these only lasting for a few days; the chances of a male and female flower being in bloom at the same time in a close enough vicinity to be pollinated is therefore extremely slim (4). In addition to these inherent factors, there is widespread habitat destruction within much of the rainforested area of Southeast Asia and Rafflesia buds are also collected for traditional medicine, to treat fertility problems, in parts of their range (5).
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Rafflesia

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Rafflesia is a genus of parasitic flowering plants in the family Rafflesiaceae. It contains approximately 28 species (including four incompletely characterized species as recognized by Willem Meijer in 1997), all found in Southeast Asia, mainly in Malaysia, Thailand and the Philippines. It was first discovered by French surgeon and naturalist Louis Deschamps in Java between 1791 and 1794, but his notes and illustrations, seized by the British in 1803, were not available to western science until 1861. It was later found in the Indonesian rainforest in Bengkulu, Sumatra by an Indonesian guide working for Joseph Arnold in 1818, and named after Sir Stamford Raffles, the leader of the expedition.

Description

"
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 (Vitaceae), spreading its absorptive organ, the haustorium, inside the tissue of the vine.[1] 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.[2] Even one of the smallest species, R. baletei, has 12 cm (5 in) diameter flowers.

The flowers look and smell like rotting flesh, hence its local names which translate to "corpse flower" or "meat flower" (see below). The foul odor attracts insects such as flies, which transport pollen from male to female flowers. Most species have separate male and female flowers, but a few have hermaphroditic flowers. Little is known about seed dispersal. However, tree shrews and other forest mammals eat the fruits and disperse the seeds.

Rafflesia is the official state flower of Indonesia, where it is known as puspa langka (rare flower) or padma paksasa (giant flower), of Sabah state in Malaysia, and of Surat Thani Province in Thailand. In Thailand, Rafflesia can be observed in Khao Sok National Park where the flowers are numbered and monitored by the park rangers.[3]

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.[1]

Name

The name "corpse flower" applied to Rafflesia can be confusing because this common name also refers to the titan arum (Amorphophallus titanum) of the family Araceae.[1] 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 only distantly related. 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. The flower is sometimes called the "monster flower" for its parasitic tendencies and foul odor.[2]

Classification

"
Rafflesia keithii bloom, approximately 80 cm in diameter near Taman Nasional Rafflesia Bengkulu - Indonesia
"
Rafflesia kerrii flower near Langkat, South Sumatra - Indonesia
"
Three Rafflesia pricei growing in close proximity near Mount Kinabalu, Sabah, Malaysia
"
New hypothesis of Rafflesiaceae derived from within Euphorbiaceae: Rafflesiaceae in red, Euphorbiaceae in black (redrawn from Davis et al., 2007)

Comparison of mitochondrial DNA (mtDNA) sequences of Rafflesia with other angiosperm mtDNA indicated this parasite evolved from photosynthetic plants of the order Malpighiales.[4] Another study from that same year confirmed this result using both mtDNA and nuclear DNA sequences, and showed the three other groups traditionally classified in Rafflesiaceae were unrelated.[5] A more recent study more specifically 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.[6] 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.

Verified species

Unverified species

Bornean species

Species native to Borneo include Rafflesia arnoldii, Rafflesia cantleyi, Rafflesia hasseltii, Rafflesia keithii, Rafflesia kerrii, Rafflesia pricei, and Rafflesia tengku-adlinii. R. arnoldii boasts the world's largest single bloom.[7] Some endemic Borneon species, such as R. keithii, begin blooming at night and start to decompose only two to three days later. The time from bud emergence to flowering is six to nine months. Male and female flowers must be open simultaneously for pollination to occur, hence successful pollination and fruit production are quite rare. In addition to habitat loss, these reproductive limitations are contributing factors to why many species are endangered. R. keithii is found along the eastern slopes of Mount Kinabalu in the Lohan Valley of Sabah. Rafflesia tuan-mudae is endemic to only Gunung Gading National Park in Sarawak.

Mindanao (Philippines) species

The Mindanao species is known as Rafflesia schadenbergiana, after the naturalist Alexander Schadenberg, who first discovered the species at the foothills of Mount Apo in 1882. With a flower of nearly a meter, it is close to the size of a 7 year old child when seated. On Mindanao, the species has been seen in Davao del Sur, South Cotabato and Mount Kitanglad in Bukidnon.[8] Second, Rafflesia mira and Rafflesia magnifica are two names for a single species. Both were discovered at Mount Candalaga in Maragusan, Compostela Valley. The two forms differ in size measurements in which the scientific description of Magnifica came from measurements of flowers in full bloom while that of Mira was from photographs of nearly dead samples. The medium-sized Mira and Magnifica flowers measure about half a meter and they have round or elliptic perigone wart.[9] The third species on Mindanao is the Rafflesia mixta which is found so far only in the town of Mainit, Surigao del Norte. It shows a combination of three features of Philippine Rafflesia, namely: the shape and size of the conical process in Rafflesia schadenbergiana, the floral size and sparsely distributed perigone warts of R. speciosa, and the overall resemblance, floral size, faint scent, diaphragm and ramenta morphology of R. mira.[10] Fourth, is Rafflesia verrucosa which is found only in Mount Kampalili in Davao Oriental Province.[11]

Loss of the chloroplast genome

Research published in the journal Molecular Biology and Evolution revealed that one Philippine Rafflesia species from the island of Luzon, Rafflesia lagascae (formerly described as R. manillana), has lost the genome of its chloroplast and it is speculated that the loss happened due to the parasitic lifestyle of the plant.[12]

See also

References

  1. ^ a b c Shaw, Jonathan (March–April 2017). "Colossal Blossom: Pursuing the peculiar genetics of a parasitic plant". Harvard Magazine. Retrieved 27 June 2017.
  2. ^ a b Scottie Andrew. "Scientists just found one of the world's largest flowers blooming in an Indonesian jungle". CNN. Retrieved 5 January 2020.
  3. ^ "Where to see Rafflesia in Thailand – the biggest flower in the world". 203 Challenges.
  4. ^ Barkman, T. J.; S.-H. Lim; K. Mat Salleh; J. Nais (January 20, 2004). "Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world's largest flower". PNAS. 101 (3): 787–792. doi:10.1073/pnas.0305562101. PMC 321759. PMID 14715901.
  5. ^ Nickrent, D. L.; A. Blarer; Y.-L. Qiu; R. Vidal-Russell; F. E. Anderson (October 20, 2004). "Phylogenetic inference in Rafflesiales: the influence of rate heterogeneity and horizontal gene transfer". BMC Evolutionary Biology. 4: 40. doi:10.1186/1471-2148-4-40. PMC 528834. PMID 15496229.
  6. ^ Davis, C. C.; M. Latvis; D. L. Nickrent; K. J. Wurdack; D. A. Baum (January 11, 2007). "Floral gigantism in Rafflesiaceae". Science. 315 (5820): 1812. doi:10.1126/science.1135260. PMID 17218493.
  7. ^ "Rafflesia Facts - Rafflesia, The World's Largest Bloom". RafflesiaFlower.com. Retrieved 14 September 2016.
  8. ^ Barcelona, J.F., P.B. Pelser, A.M. Tagtag, R.G. Dahonog & A.P. Lilangan. 2008. The rediscovery of Rafflesia schadenbergiana Göpp. ex Hieron. (Rafflesiaceae). Flora Malesiana Bulletin 14: 162-165.
  9. ^ Madulid, D.A.; Tandang, D.N. & Agoo, E.M.G. (2008). "Rafflesia magnifica". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 22 November 2013.
  10. ^ M.E. Manting, R.B. Arbolonio, R.B. Caballero & P.B. Pelser. 2014. Rafflesia mixta (Rafflesiaceae), a new species from Surigao del Norte, Mindanao, Philippines
  11. ^ Balete, D.S., P.B. Pelser, D.L. Nickrent & J.F. Barcelona. 2010. Rafflesia verrucosa (Rafflesiaceae), a new species of small-flowered Rafflesia from eastern Mindanao, Philippines. Phytotaxa 10: 49-57.
  12. ^ Molina, Jeanmaire; Hazzouri, Khaled M.; Nickrent, Daniel; Geisler, Matthew; Meyer, Rachel S.; et al. (2014). "Possible Loss of the Chloroplast Genome in the Parasitic Flowering Plant Rafflesia lagascae (Rafflesiaceae)". Molecular Biology and Evolution. 31 (4): 793–803. doi:10.1093/molbev/msu051. PMC 3969568. PMID 24458431.
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Rafflesia: Brief Summary

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Rafflesia is a genus of parasitic flowering plants in the family Rafflesiaceae. It contains approximately 28 species (including four incompletely characterized species as recognized by Willem Meijer in 1997), all found in Southeast Asia, mainly in Malaysia, Thailand and the Philippines. It was first discovered by French surgeon and naturalist Louis Deschamps in Java between 1791 and 1794, but his notes and illustrations, seized by the British in 1803, were not available to western science until 1861. It was later found in the Indonesian rainforest in Bengkulu, Sumatra by an Indonesian guide working for Joseph Arnold in 1818, and named after Sir Stamford Raffles, the leader of the expedition.

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