Rafflesia arnoldii
(c) ccgfh, some rights reserved (CC BY-NC)
I hope you didn’t hear Radio 4 last Monday morning at 9. If you did you can stop reading now…or maybe you were as absorbed as I was and want to find out even more about Rafflesia. “Start The Week”| is not a programme I usually listen to but this week it was all about plants, and had the inspirational botanist Chris Thorogood from Oxford Botanic Garden talking about his latest trip to south east Asia to help conserve this extraordinary plant which has the largest flowers in the world.
As soon as the programme had finished I started this post and if you read on you’ll see why, even though its unlikely you’ll ever be able to grow one at home, or even see one in one of our great botanic gardens any time soon.
Images without captions or attributions are screenclips from The Green Planet on YouTube
Rafflesias are a bizarre group of plants, to put it mildly. To start with they have no leaves, or stems, and their only visible part is the flower, but since they don’t flower very often its extremely hard to find them in their remote jungle home across Indonesia, Malaysia, Brunei, the Philippines and Thailand.
There are thought to be over 40 species and they all produce large flowers – even the smallest can be the size of a dinner plate – but on the biggest, Rafflesia arnoldii, they can be enormous – well over a metre in diameter, and potentially weighing over 10kg. This makes them the world’s largest flower, with one found on a specimen in Sumatra in 2019 being 120cm across.
The flowers of all Rafflesia species are in mottled shades of brick-red with white or paler blotches, for a very clever reason as we’ll see shortly. They have 5 petals, which I’ve seen described as soft, leathery or even spongey, and which are covered with wart-like lumps and bumps.
In the centre is a deep, cup-shaped chamber – described by one observer as being like a planetarium or astronomical observatory with a roof partially opened to the sky. Inside, at the base is a large pale disc covered with a scary set of spikes, and surrounded by softer fine hairs.
Rafflesia arnoldii
(c) ccgfh, some rights reserved (CC BY-NC)
Even stranger is the fact that, not only do they not have leaves or stems but Rafflesias don’t have roots either. This is because the plant is a highly specialised form of parasite and live in and on vines in the genus Tetrastigma.
Instead, to obtain water and nutrients they have root-like structures known as haustoria, which burrow into the host plant in much the same way that broomrape, mistletoe and fungi predate their host plants.
Charles Davis, professor of evolutionary biology at Harvard describes the Rafflesia’s way of obtaining its sustenance as rather like making “an illegal connection to the electrical grid.” Tetrastigma vines hold large quantities of water, and the Rafflesia can draw on this at will, especially when it is needed for the final stages of flower development. In fact when open its flowers are actually mostly water and Davis goes on to say they feel like “a Nerf football that is wet,” [Don’t worry I had to look it up too! -its a type of sponge ball]
But Rafflesia are not just parasitic, they are perhaps the most extreme parasitic plant known because not only do they live inside the vine, and feed off it but Davis discovered when he sequenced their genomes that they take more than just water and nutrients. They also take some of their hosts genes. This process, known as horizontal gene transfer, was thought usually only to occur in the lowest levels of lifeforms such as bacteria. It means, says Davis that “the host and parasite share so much biology that the boundaries between them have become blurred.” He suggests although while it’s possible this could be an evolutionary dead end it seems more likely to be “a powerful, alternative means by which Rafflesia maintain their fitness: by co-opting the genes of their hosts.” 
Back to the flowers and their unusual colouring. As I’m sure you guessed they have evolved to look like lumps of rotting meat and they stink of it too. This makes them part of a range of plants, not otherwise related in anyway such as the titan arum, skunk cabbage and stapelia, which have large smelly flowers that resemble carrion and attract carrion flies to pollinate them. To prove his point Davis used vacuum pumps to capture the smell and had it analysed only to find that the chemical profiles were indeed very similar to that of rotting meat. Since carrion flies are apparently attracted to larger rather than smaller piles of dead stuff Davis goes on to suggest that “There seems to be an association, between gigantism [in flower size] and plants that reek of rotten flesh.“
So, lets look at the life cyle of the Rafflesia, although even now it’s not fully known. The flowerbud emerges from the vine’s bark looking like a small orangey-brown cabbage with tightly furled leaves. This can take between 6 and 9 months to fully form.
As the flower opens it warms up, producing heat to help to spread its distinctive smell which emanates from the base of the flower deep inside the central cup. The carrion flies arrive, go down into the flower in search of their dinner but obviously don’t find any. In the process they get covered in pollen. As you can see from the photo of the fly above, whilst in almost every other plant pollen is powdery, in Rafflesia, Davis notes it is “produced as a massive quantity of viscous fluid, sort of like snot, that dries on the backs of these flies.”
It’s thought to remain viable for quite a long time, and can be transported up by the flies to 12 miles before pollinating another flower in a reverse of the original process. Even so because of the rarity of simultaneous flowering successful pollination and fertilisation are not frequent occurrences.
In less than a week the flower dies and within a few more days just dissolves into a puddle of black slime. Amidst the goo of decaying female flowers are its fruits which, according to Davis look like “a manure pie, filled with hundreds of thousands of tiny seeds”. Each millimetre long seed is surrounded by a little blob of oil which is extremely attractive to ants.
The fruit are either eaten by various small creatures whose droppings disperse the seeds, or they rot and the seeds thus become available to the ants who take them to feed the oily part to their larvae. The ants are not interested in the seeds themselves so they are taken and dumped in their waste disposal arena [I didn’t know that ants had such spaces but apparently they do!]. Because this area contains all sorts of other rotting materials and is quite warm because of the heat created by decomposition with any luck a few seeds might germinate near a vine root. That’s not certain but merely informed guesswork because it is known that other forest-floor plants like trillium and violets, have similar oil components, and are dispersed by ants.”
What intrigued me was how the Rafflesia managed to get itself into the host vine in the first place. It appears that the ants might help there too. Vines sometimes secrete a sugary water if their bark is scratched or damaged perhaps by a passing animal, or perhaps the ants chew into the bark in search of it. But actually the real answer is nobody knows.
Rafflesia have only been known to westerners since the first known sighting in Java by the French surgeon and naturalist Louis Deschamps in the 1790s but news didn’t reach Europe for decades because this was during wars with Britain and his drawings and notes were captured by the Royal Navy in 1803 and didn’t get “rediscovered” until 1861.
By then it had already been scientifically described and named in the Journal of the Linnean Society for 1822. The article, as first read to the Society in June 1820 by Robert Brown the society’s librarian, tells the story of its discovery – of “what I consider as the greatest prodigy of the vegetable world” by Joseph Arnold, another surgeon naturalist and fellow of the Linnean Society, in May 1818.
The article was accompanied by no less than 8 engravings of the flower and its parts by Franz Bauer, based on Arnold’s original drawings.
Arnold had just started out on a collecting trip with Sir Stamford Raffles, then the Governor of the East India Company’s establishments in Sumatra, “when one of the Malay servants came running to me with wonder in his eyes, and said, come with me, Sir, come! a flower, very large, beautiful, wonderful!”
I immediately went with the man about a hundred yards in the jungle, and he pointed to a flower growing close to the ground under the bushes, which was truly astonishing. My first impulse was to cut it up and carry it to the hut. I therefore seized the Malay’s parang (a sort of instrument like a woodman’s chopping-hook), and finding that it sprang from a small root which ran horizontally (about as large as two fingers, or a little more), I soon detached it and removed it to our hut. To tell you the truth, had I been alone, and had there been no witnesses, I should I think have been fearful of mentioning the dimensions of this flower, so much does it exceed every flower I have ever seen or heard of; but I had Sir Stamford and Lady Raffles with me, and Mr. Palsgrave, a respectable man resident at Manna, who, though equally astonished with myself, yet are able to testify as to the truth”. However “a guide from the interior of the country said, that such flowers were rare, but that he had seen several, and that the natives called them Krábát.”
Arnold then went on to describe the flower in great detail including the fact that “a swarm of flies were hovering over the mouth of the nectary, and apparently laying their eggs in the substance of it” and that it “had precisely the smell of tainted beef” and was “a full yard across “.
“Sir Stamford, Lady Raffles and myself taking immediate measures to be accurate in this respect, by pinning four large sheets of paper together, and cutting them to the precise size of the flower. The nectarium in the opinion of all of us would hold twelve pints, and the weight of this prodigy we calculated to be fifteen pounds.”
Unfortunately the specimen flower itself did not reach England because “It was not examined on the spot, as it was intended to preserve it in spirits and examine it at more leisure; but from the neglect of the persons to whom it was intrusted, the petals were destroyed by insects.”
Nevertheless Sir Stamford’s letters and Arnold’s drawings were enough to cause a sensation, and the article about the discovery in the Linnean Journal. From there news spread rapidly and reports of Rafflesia were published in French, German, Swedish and American botanical journals too. Brown followed the original piece up with another article and series of engraving in the 1844 Journal.
The next obvious thing would have been for seeds or plants to have been sent back to Kew and grown in the hothouses there. I’m sure this was tried but until very recently all attempts to cultivate R. arnoldii outside its native habitat have failed miserably.
That lack of success lasted until around 2000 when Jamili Nais, a Malaysian biologist , became the first to propagate plants from seeds and even more recently in September 2022 The Jakarta Post reported that Sofi Mursidawati, a researcher at the Plant Conservation Centre of Bogor Botanical Garden on Java [formerly under the Dutch this was Buitenzorg BG] , who had been trying to cultivate the flower there for the last 16 years had finally coaxed one into flower. It followed on her earlier breakthrough with the successful cultivation of Rafflesia patma at Bogor. However it’s not quite as straightforward as it seems. The bud mortality rate is 90 percent and none of the plants she has raised have bloomed at the same time so there’s been no pollination and no viable seed. For more on her work see this article in National Geographic.
The way that is currently being trialled is to take cuttings of “Rafflesia invaded” vine and graft them on to “clean” stock and hope that the root-like structures [haustoria,] are able to regrow and colonise their new hosts.
You’d think that being such an extraordinary plant group Rafflesia would be safe and well protected but the truth is exactly the opposite with most of the genus now on the brink of extinction. A study published last September found that most of the 42 species are severely threatened, but only one has been listed in the International Union for Conservation of Nature (IUCN)’s Red List of Threatened Species. Furthermore, over two thirds (67%) of the plants’ habitats are unprotected and at risk of destruction. It doesn’t help that Rafflesia species have a limited dispersal capacity or that most species are restricted to a single island, [only five are known to grow on more than one]. Even within those limits most species are known only in one or two localities, with some having been collected just once .
Chris Thorogood, deputy director of Oxford Botanic Garden, and one of the authors of the study, argues that because, apart from flowering times, Rafflesia are hidden throughout their life cycle, they are poorly understood, and although new species still being found many populations are believed to contain only a few hundred individual plants.
It just “highlights how the global conservation efforts geared towards plants – however iconic – have lagged behind those of animals… and how we urgently need a joined-up, cross-regional approach to save some of the world’s most remarkable flowers.”
Yet as Adriane Tobias, a forester from the Philippines and another of the authors, has said. “Rafflesia has the potential to be a new icon for conservation in the Asian tropics.” They are striking enough to capture the popular imagination and could be “the panda of the plant world”. Already the national flower in Indonesia, and on stamps and currency, and appreciated for its medicinal and culinary properties it has considerable further potential. Encouraging ecotourism would allow local communities to benefit from Rafflesia conservation, rather than destroying their habitat in slash and burn subsistence farming. “Indigenous peoples are some of the best guardians of our forests, and Rafflesia conservation programmes are far more likely to be successful if they engage local communities.”
Rafflesia are rightly celebrated, lets hope that the conservation programmes currently underway keeps enough 0f them alive for them to be celebrated for generations to come.
You can hear Chris Thorogood talking about efforts to conserve Rafflesia on 28th March 2024 – free tickets in association with the Linnean Society, available via Eventbrite.
See you there!
For further information good places to start are the on-line article in People, Plants and Planet, “Most of the world’s largest flowers (genus Rafflesia) are now on the brink of extinction” by Pastor Malabrigo and others, Sept 2023; for more on Charles Davis’s work see “Colossal Blossom: Pursuing the peculiar genetics of a parasitic plant” by Jonathan Shaw in Harvard Magazine, 2017; For more on the issues around propagating Rafflesia see Carlos Ordonez-Parra, “Unlocking the Tiny Secrets to Grow the World’s Largest Flowers” on the Botany One website, October 2023. There are also several youtube videos as well, although not all are completely accurate…and, last but not least the Start the Week programme broadcast on Monday 4th March 2024, which will be available for at least a year
The Gardens Trust 
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