The Largest Flower in the World Smells Like Rotting Meat and Is Named After Stamford Raffles

The Rafflesia arnoldii flower is the largest single bloom of any flowering plant species in the world. A mature specimen is about 1 metre across, weighs roughly 7 kilograms, has five thick fleshy petals of a brick-red colour mottled with pale spots, and produces a strong smell of rotting meat to attract the carrion-feeding blowflies that pollinate it. The flower opens for about five days and then collapses into a black slimy mass that decomposes within a week.

The plant has no leaves, no stem, no roots, and no chlorophyll. It is a holoparasite — every metabolic function it cannot perform itself is taken from a single host genus, the woody vine Tetrastigma, into which the Rafflesia embeds its filamentous body. The only visible part of the plant is the flower, which erupts from the surface of an infected vine like a fungus and is the only sign that the parasite is present at all.

It was first reported to European science in May 1818 by a small British East India Company expedition led by Stamford Raffles, then Lieutenant-Governor of the British colony of Bencoolen on the west coast of Sumatra.

The expedition

Raffles had been appointed to Bencoolen in 1817, after losing the Java governorship to the Dutch in the post-Napoleonic colonial settlement. Bencoolen was a backwater — a hot, fever-ridden coastal pepper-trading post that the East India Company had run unprofitably since 1685 — and Raffles spent much of his five years there exploring the Sumatran interior and cataloguing its natural history.

The May 1818 expedition was a two-month overland trek into the Pulau Lebar district about 150 kilometres inland from the Bencoolen coast. The party included Raffles, his wife Sophia, his deputy Lewis Watson Presgrave, and the expedition’s medical officer Joseph Arnold, a 36-year-old Norwich-born surgeon-botanist who had joined the British East India Company in 1815 as a ship’s surgeon and had attached himself to the Raffles household earlier in 1818.

On about 19 May 1818, a few days into the inland march, one of the Malay porters showed Arnold a giant flower he had spotted at the base of a vine in the forest off the path. Arnold’s diary entry for that day records his reaction: “I rejoice to tell you that I happened to meet with what I consider the greatest prodigy of the vegetable kingdom… It measured a full yard across, weighs fifteen pounds, and contains a measure and a half of nectarines.”

The party recorded the find, took several specimens, made watercolour drawings, and pressed dried portions of the flower in their botanical presses. Raffles immediately recognised the find as a new genus and named it provisionally Rafflesia — pending formal description by a competent European taxonomist.

What happened to Arnold

The expedition returned to Bencoolen in early July 1818. Arnold had caught a fever during the trip and was visibly unwell when the party arrived back at the coast. The fever progressed rapidly. He died at the Raffles residence on 26 July 1818, eight weeks after finding the flower that would carry his name. He was 36.

The cause was almost certainly malaria — the same disease that killed approximately a third of the European population of Bencoolen during any given decade of the colony’s existence and that Joseph Arnold’s medical experience had not protected him against. His grave is in the small European cemetery at Fort Marlborough in modern Bengkulu. The headstone is intact.

His botanical specimens were sent to London via the next available East India Company vessel, with Raffles’s covering letter requesting that the new genus be formally described by Robert Brown, the senior botanist of the Linnean Society of London and the foremost British plant taxonomist of the period. Brown received the material in late 1819, performed the formal taxonomic description, and presented the new species to the Linnean Society on 20 June 1820 as Rafflesia arnoldii — Raffles for the patron of the expedition, Arnold for the discoverer who had not survived to see his name in print.

The earlier Deschamps find

It later turned out that Rafflesia arnoldii was not actually new to European science. A French naval surgeon named Louis-Auguste Deschamps had found a closely-related species (now classified as Rafflesia patma) on Nusakambangan island off the south coast of Java in 1797, during the French scientific expedition that had been led by Jean-Baptiste Marchand. Deschamps had written a complete botanical description and made detailed drawings.

His papers and specimens were impounded by a British naval ship in 1803 when Deschamps was returning to France and were held in the British Admiralty archives for the next 58 years. The Deschamps Rafflesia material was rediscovered in 1861 by the British botanist William Hooker (then Director of the Royal Botanic Gardens at Kew), who published a partial recovery of the Deschamps material in 1862. The Deschamps priority was acknowledged in the taxonomic literature but the Brown name Rafflesia arnoldii (with the Raffles dedication) was retained as the established type-species name under the priority rules of the International Code of Botanical Nomenclature.

Why it matters

There are about 28 recognised species of Rafflesia, all of them parasitic on Tetrastigma vines, all of them native to the rainforests of Southeast Asia (Sumatra, Borneo, Peninsular Malaysia, the Philippines, southern Thailand). The Rafflesia arnoldii of Sumatra is the largest of the genus. The genus Rhizanthes, a close relative, also belongs to the same family of bizarre parasitic flowering plants and is also restricted to the same Southeast Asian rainforests.

The genus is endangered. Rafflesia depends on intact primary rainforest for its host vines, which depend in turn on intact primary rainforest for their fig and dipterocarp ecology. The clearing of Indonesian and Malaysian rainforest for palm-oil plantations through the late 20th and early 21st centuries has reduced the available habitat by perhaps 70% over fifty years. Several of the rarer Rafflesia species are believed to be functionally extinct.

The flower’s smell — the rotting-meat odour that attracts the pollinating blowflies — is produced by the same dimethyl-disulphide and dimethyl-trisulphide compounds that human noses detect in spoiling animal protein. The smell is strongest in the first 24 hours after the bloom opens and tapers off through the five-day flowering period. A few enterprising Sumatran villages near known Rafflesia habitats have built small ecotourism operations around the rare events when a bloom is open; visitors typically last about three minutes in the immediate vicinity of an open flower before retreating to a more downwind position.