Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592
Kew Species Profiles
This southeast Asian plant has the largest known individual flower in the world. It is parasitic on members of the genus Tetrastigma (in the grape family, Vitaceae). It has no roots or leaves and most of the time lives unobserved inside the woody stems and roots of its host. Rafflesia arnoldii only becomes visible when its plump buds emerge through the bark of its host and develop into the large, fleshy flowers which are pollinated by carrion-flies.
Known from the southeast Asian islands of Sumatra and Borneo, where it occurs in primary and secondary forest, up to 1,000 m above sea level.
DescriptionRafflesia arnoldii is a parasitic plant, without roots or leaves. The main body of the plant resides inside the host plant. The only visible parts are the flowers, which burst through the host plant's bark as compact buds, and later the fruits. The flowers are up to 1 m in diameter, and their flesh is reddish-brown with white spots. Each flower is either male or female and consists of five lobes inserted on a cup-like structure. In the centre of the cup is a column with a disk. The anthers (male parts) or styles (female parts) are situated underneath the disk. The fruits are berries with minute seeds.
It is likely that only damaged roots or stems of a new host can be infected by seedlings of Rafflesia . The foetid smell of the flowers attracts carrion-flies (of the genera Lucilia and Sarcophaga ). The pollen adheres to the backs of the flies, which do not seem to receive any reward from the plant.
Two varieties are known, the more common being R. arnoldii var. arnoldii from Sumatra and Borneo, the other one being R. arnoldii var. atjehensis which is only known from north Sumatra. The main difference between the two is that the central disk (or ramenta) is partly missing at the base of the central column in R. arnoldii var. atjehensis .
A race for discoveryThe first botanist to find a specimen of a Rafflesia was the French explorer Louis Auguste Deschamps (1765-1842). He was a member of a French scientific expedition to Asia and the Pacific. During the expedition he spent three years on Java, where in 1797 he collected a specimen of what is now known as R. patma . During the return voyage in 1798, his ship was taken by the British, with whom France was at war, and all his papers and notes were confiscated. They did not see the light of day until 1954 when they were rediscovered in the Natural History Museum, London.
The British botanist Joseph Arnold (1782-1818) and the statesman Sir Thomas Stamford Bingley Raffles (1781-1826, founder of modern Singapore) collected a specimen of another Rafflesia species found by a Malay servant in Sumatra in 1818. Arnold contracted a fever and died soon after the discovery. Lady Raffles, who had also been present when the specimen was collected, finished the colour drawing that Arnold had started of the plant, and it was sent to Joseph Banks, along with the preserved material. Banks passed all the materials on to Robert Brown (1773-1858) of the British Museum and Kew's resident botanical artist Franz Bauer (1758-1840).
William Jack (1795-1822) who was Arnold's successor in Sumatra, being aware that Deschamps, despite his loss of notes, could formally publish a name for the newly discovered genus at any moment, rushed to draft a description to ensure the credit went to a British botanist. This draft description was held in readiness, in case there was word that the French were about to publish, whilst waiting for the British Museum to produce a better-prepared version.
The generic name, Rafflesia (given in honour of Sir Raffles), proposed by Brown (who had originally wanted to call it Arnoldii ) after Joseph Arnold, was validated by S.F. Gray in his report of the June 1820 meeting of the Linnean Society of London, as published in the Annals of Philosophy in September that year. While the species Rafflesia arnoldii was officially described for the first time in 1821 by Brown, so that Arnold was commemorated after all.
Threats and conservationMany sites where Rafflesia grows are now popular with tourists, who provide an income for local people and also an incentive to preserve the species. Unfortunately, as a result of this ecotourism and the resulting human disturbance, the number of flower buds produced per year has decreased significantly at many sites.
UsesThe flower buds are applied in traditional medicine to promote delivery and recovery during and after childbirth. They are also used as an aphrodisiac. It is likely that these uses are associated with the shape, colour and size of the buds, and superstitions surrounding the flower, rather than being linked to any chemical properties.
The flower of Rafflesia arnoldii is an iconic symbol of the southeast Asian rainforest, and is often used in tourist brochures to symbolise the rich biodiversity of the region's forests. The flower has also been depicted on Indonesian postage stamps on several occasions, while the flowers of related Rafflesia species are often illustrated on the postage stamps of neighbouring southeast Asian countries. The flower is also used as the symbol of the Flora Malesiana project, which aims to describe all flowering plants from the region between Thailand and Australia.
Areas of forest in which Rafflesia arnoldii grows are visited by ecotourists, providing an income for local people and revenue for protected areas. The fruits are eaten by ground squirrels and tree shrews.
CultivationThere are a number of reports of Rafflesia plants being grown in cultivation, but it is usually assumed that this is the result of transplanting the host plant rather than successful artificial infection of a healthy host in cultivation.
Where to see this at KewRafflesia arnoldii has never been grown at Kew, but a wax model is exhibited in Museum No. 1. The wax model was obtained from the Horticultural Society in 1855, having originally been made at a cost of £20. The model was seen by J. Hunt Cooke who immortalized it in verse in 1877:
What strange gigantic flower is hereThat shows its lonesome pallid faceWhere neither stems nor leaves appear
A preserved specimen of Rafflesia arnoldii is held in Kew's Herbarium. An alcohol-preserved flower of Rafflesia arnoldii is held in Kew's Economic Botany Collection, where it is available to researchers by appointment.
None known.
