Millennium Seed Bank blog
Welcome to the Millennium Seed Bank blog. There is a lot going on behind the scenes at Kew's Millennium Seed Bank (MSB) - not only here at Wakehurst but also with our partners all over the globe. We will be blogging about our seed collecting trips, local events, research projects and discoveries as well as everyday goings on.
We currently have seeds from more than 30,000 species of wild plants in long term storage and continue to receive seed collections from all over the world. It is an amazing place to work and we hope to share our passion for seed conservation with you via our blogs.
Grass pea is a crop with two sides to its personality. Considered both a saviour and a destroyer, in times of famine grass pea is often the only alternative to starvation. Being the hardy plant that it is it can withstand extreme environments, from drought to flooding, and when all other crops fail grass pea will often be the last one left standing. It is easy to cultivate, and is tasty and high in nutritious protein, which makes grass pea a popular crop in south west Asia and the eastern Horn of Africa where it is also grown to feed livestock. Being a member of the legume family, Lathyrus is able to fix nitrogen from the air which means that growing it keeps the soil healthy and well fertilised.
Pretty Poisonous - a grass pea in flower (Photo credit: Nancy J. Ondra)
Now, before we make a saint out of the humble grass pea, let us consider some of its more sinister attributes. Eaten in small quantities, grass pea is harmless. However, eating it as a major part of the diet over a three month period can cause permanent paralysis below the knees in adults and brain damage in children, a disorder known as lathyrism. The culprit is a potent neurotoxin called ODAP. This is responsible for the drought and waterlogging tolerance of grass pea but, if taken in large quantities, it brings on the neurological disorder. For example, Ethiopia has seen several lathyrism epidemics in the past 50 years, when hunger overrules the dangers inherent in grass pea consumption. What makes matters worse is that the level of the neurotoxin increases in the crop under conditions of severe water stress which exacerbates the risk of lathyrism at a time when the poorest of the poor have no choice but to rely on the crop for their survival.
According to The Consultative Group on International Agricultural Research (CGIAR) at least 100,000 people in developing countries are believed to suffer from paralysis caused by the neurotoxin. There are a number of ways of preparing grass pea so that it is less harmful, for example, by washing and soaking the grass peas and then discarding the water before cooking or by eating grass pea mixed in with other crops. Both strategies are effective in reducing the risk of lathyrism however in a famine where water and other food sources are scarce, detoxification of grass pea may be harder to implement.
Bags of grass pea sold at a maket in Florence, Italy (Photo credit: Dirk Enneking, Institute for Plant Genetics and Crop Breeding)
Thanks to the Grasspea
The adverse neurological effects of eating grass pea have been known since prehistoric times. Ancient Indian texts described the disorder and even Hippocrates, the father of modern medicine himself, mentions a neurological disorder caused by eating a Lathyrus seed in 46 B.C. in Greece. Grass pea was served as a famine food during the Spanish War of Independence against Napoleon and below is one of Francisco de Goya’s famous aquatints, Gracias a la Almorta ("Thanks to the Grasspea"). It captures the hardships of the time through its depiction of the poor surviving on grass pea porridge, one of them lying on the floor, already crippled by it. I’m still scratching my head over whether Francisco de Goya was being sarcastic or not when he chose that title – such is the paradox that grass pea presents!
Francisco de Goya's aquatint "Gracias a la almorta" translated to "Thanks to the grass pea". (Photo credit: Wikipedia Commons)
“Why not just abandon the cultivation of this so-called food crop?!” I hear you say. Well, it is not as straightforward as that. Grass pea continues to be the ultimate safety net for subsistence farmers in the poorest parts of the world and provided that consumption does not reach that critical level it is safe and nutritious to eat. Quite simply, grass pea is too important to do away with altogether.
Breeding low toxin varieties
Crop diversity is the key to overcoming this paradox and is the only thing that can put an end to the good cop/bad cop antics of grass pea. The International Centre for Agricultural Research for Dry Areas (ICARDA) is working with Ethiopian breeders to develop cultivars of grass pea with low levels of the neurotoxin ODAP. Toxins found in African and Asian grass pea plants are seven times more toxic than the Middle Eastern varieties. The new ICARDA hybrids have levels of the toxin high enough to keep up the crop’s resilience to drought and flooding, without being damaging to human health. The Centre for Legumes in Mediterranean Agriculture (CLIMA) is also conducting important research in this area and has recently produced a low toxin variety. Hope is on the horizon but much more work needs to be done to produce locally adapted, low toxin varieties and to distribute these to farmers.
Grass pea seeds (Photo credit: Dirk Enneking, Centre for Legumes in Mediterranean Agriculture CLIMA 1995)
Crop Wild Relatives: A source of genetic diversity
The wild relatives of grass pea are an important source of genetic diversity for the cultivation of low toxin varieties. Grass pea is one of the 29 priority crops that are the focus of the Adapting Agriculture to Climate Change project executed by Kew’s Millennium Seed Bank and the Global Crop Diversity Trust. By collecting the wild relatives of crops such as grass pea and making their seeds available to breeders, useful traits such as lower toxicity levels, in the case of Grass pea, and resistance to pests, diseases and environmental stresses can be passed on to crops, making them more resilient and better equipped to deal with climate change. The development of low toxin varieties of grass pea is a matter of food security and is something that will have a direct impact on the health and livelihood of thousands of people. Grass pea takes on a special importance in the light of climate change since tolerance to drought and flooding are characteristics that give the crop an advantage in stressful conditions.
Who knows, maybe grass pea will be up for sainthood after all!
- Sarah -
2 comments on 'The curious case of the grass pea'
As a Seed Processing Assistant my role includes a range of tasks that are carried out at various times throughout the week.
These tasks include seeing the seed collections from arrival at the Seed Bank, all the way through to banking them in the vault, and beyond. The collections are dried, cleaned, x-rayed, counted, banked and then germination tested. Each day is different as, although the range of tasks is fairly limited, the material we are working on is very varied. This makes it a very exciting role and you are always learning something new!
The spiral staircase leading to the underground vault at the Millennium Seed Bank (Image: Dave Hill)
First task of the day
This morning my team are working down in the vault preparing some seed collections for storage at -20°C and, where necessary, at -190°C in cryo storage as well. By this point the collections have been cleaned, x-rayed and counted and have spent a month in the main dry room at 15% relative humidity (RH) to ensure they are dry enough for storage. We use a non-destructive Rotronic device to check that the RH of the seeds is at 17% RH or less.
A non-destructive Rotronic device is used for checking if seeds are dry enough to be banked. (Image: © RBG Kew)
Today we are banking species from Malawi. Each collection is placed in a suitably sized glass container with an indicator sachet and, using our database, a location in the freezer is allocated and labels for the containers printed.
Packaging seeds into jars for storage. (Image © RBG Kew)
Once we have repeated this process for each collection in the batch the next step is dressing up in the big blue suits to go into the freezer and put the containers in/on the relevant drawer and shelves. It is exciting to know that by lunchtime we have added seeds from another 60 species to the 1.9 billion seeds already in storage at the MSB.
Here I am ready to put the seeds in the freezer. (Images: © RBG Kew)
A different task for the afternoon
It is all change in the afternoon with x-raying to be done. Using our digital x-ray machine we can view the contents of a sample of each seed collection and determine its quality. The machine produces an image that allows us to see full, empty, infested and diseased seeds in detail. Not all collections take a great picture so in those instances we cut open some seeds under a microscope instead. We work through a number of collections until we get to this Leguminosae species; it has a number of infested seeds present, you can even see some maggots!
X-ray image of an infested Leguminosae species; the dark areas in the seeds are maggots. (Image: © RBG Kew)
Change of plan as an exciting new batch arrives
While we are working a batch arrives from the USA. An incoming batch takes priority over any other work so we pack away and clean up ready to unpack the new collections. Each batch comes with lots of paperwork and the first job is to check if any chemical treatments have been used or if any quarantine or CITES listed species are present, as these would need to be separated and handled differently.
Bags of seeds just arrived from USA. (Image: © RBG Kew)
We unpack the box inside an extraction hood and wear gloves as a precaution. In the box we find 35 seed collections with associated voucher specimens and data sheets. Using the batch list we check that seeds, voucher specimen and data are included for each species. We open and assess each seed collection and also make notes where relevant e.g. if the collection is very small.
Once unpacked the seeds are placed in a crate in the dry room.
The drying room at the Millennium Seed Bank. Air, dried using desiccant-impregnated dryers to 15% relative humidity is fed into the initial dry room which is maintained at 15°C
The vouchers are placed at -20°C for one week prior to processing, the data is entered onto our database, and the International Coordinator for the USA is informed that the batch has arrived safely. By the time we have finished clearing up it is 5pm and time to go home.
- Angie -
0 comments on 'A day in the life of a Seed Processing Assistant'
If you get excited by exotic fruits, here’s one that adds a little ‘creep factor’ to the experience. Best of all, you can even grow it in your own garden in the UK and use it as a party trick to freak your friends!
The fruit of Decaisnea insignis, also called ‘dead man’s finger’ (Photo: W. Stuppy)
Freaky blue fruit
The freaky fruit I am referring to here is kind of a secret delicacy. It’s been enjoyed for centuries by the Lepcha, the indigenous people of Sikkim, but outside its natural range the dead man’s finger is little known for its edible fruits. A member of the chocolate vine family (Lardizabalaceae), Decaisnea insignis is a shrub native to China, Nepal, northeast India (Sikkim), Bhutan, and Myanmar. At home in Asia it grows at altitudes between 900 to 3600 metres above sea level which is why it is frost-hardy in the UK where it is sometimes grown as an ornamental.
Left: a female flower of the chocolate vine (Akebia quinata), a popular garden plant with chocolate-scented flowers; right: a female flower of its close relative, the lesser known Decaisnea insignis (Photo: W. Stuppy)
Like a cold human finger
The greenish-yellow flowers of Decaisnea are between 3-6 cm in diameter and borne in drooping racemes. They come in separate male and female flowers but it is only the latter ones that give rise to Decaisnea’s most striking decorative feature, the very unusual finger-like blue fruits. About 7-12 cm long, soft to the touch and covered in an eerily skin-like peel, the fruit of Decaisnea does really feel like a cold human finger, hence it’s common name ‘dead man’s finger’.
The fruits of Decaisnea insignis are always borne in clusters of three (Photo: W. Stuppy)
One flower – three fruits
The fruits of Decaisnea are borne in clusters of three and this has got an interesting reason. Normally you would expect one fruit per flower but in Decaisnea, each female flower contains three separate carpels (the three straight cylinders in the centre; see photo above). Because the three carpels are free from each other, after successful pollination, each one of them turns into a fruit of its own. Actually, ‘fruitlet’ would be the botanically correct term for one of these fingers, the diminutive indicating the origin of a triplet of ‘fingers’ from one flower.
The fruit of Decaisnea insignis opens along a straight line to reveal the edible gelatinous pulp (Photo: W. Stuppy)
The taste of a dead man’s finger
Now comes the really interesting part. Almost as if opening with a zip, the fruits easily split along a straight line to reveal their translucent gelatinous pulp into which a large number of flat black seeds are embedded in two rows. The jelly-like pulp is the edible part, not the hard seeds. Having tasted my first dead man’s finger with great curiosity and excitement, I found its flavour very pleasant and subtle, mainly sweet, perhaps with a hint of melon or cucumber.
Unzipped – the fruit of Decaisnea insignis opened up along its ventral suture, like the carcass of a slaughtered animal, ready to be gutted. Yum! (Photo: W. Stuppy)
A bit of seed morphology
O.K. this is a bit nerdy but since I am a Seed Morphologist and information about the inner workings of the seed of a dead man’s finger is not something you can easily find anywhere else, I might as well... The seeds of Decaisnea insignis are about 1 cm long and about 3-4 mm thick. Inside the seeds bear a very small embryo embedded in copious nutritious tissue (endosperm) which the embryo consumes during germination.
A longitudinal section through the seed of Decaisnea insignis showing the very small embryo embedded in copious endosperm (Photo: Gemma Toothill)
The usual question: who is it meant for?
When I come across such weird fruits like the dead man’s finger I always want to know how they are dispersed naturally. Offering a sweet edible pulp, the fruits of Decaisnea insignis are obviously meant to be eaten by some animal but which one? Little can be found in the literature about Decaisnea’s natural dispersers. However, the size of the fruit (too big for most birds in its native range) and the fact that it obviously requires peeling (a bit like a banana) to separate the edible pulp from the thick leathery peel suggests that animals with a good degree of ‘manual’ dexterity are the co-adapted dispersers of Decaisnea insignis. Indeed, the only information in the scientific literature I could find about potential dispersers is that in China (Yunnan & Szechuan), snub-nosed monkeys (Rhinopithecus spp., Cercopithecidae) include fruits of Decaisnea in their diet [Dietary profile of Rhinopithecus bieti and its socioecological implications].
Whether snub-nosed monkeys are really the co-adapted dispersers of Decaisnea is hard to say because primates in general are intelligent and may learn to eat any fruit, even if is not ‘meant’ specifically for them. Also, this would not necessarily explain the fruits’ very unusual blue colour. Snub-nosed monkeys possess trichromatic vision like us humans and so the fruits could as well be some shade of red or yellow, which is a much more common fruit colour. If any readers would have more information towards solving the riddle of the natural disperser of Decaisnea, I would like to hear from them.
Just in case you wondered....
Some readers might be more familiar with the Latin name Decaisnea fargesii for the dead man’s finger. Indeed, on the basis of its blue fruits, D. fargesii from China (the most common form in cultivation) has been considered as a separate species from the Nepalese D. insignis with yellowish-green fruits. However, fruit colour alone is not considered a strong enough character to justify the separation into two species which is why some authors have combined both species into one, i.e. Decaisnea insignis (e.g. Flora of China, Mabberley’s Plant Book).
Danger! Don’t just eat any dead man’s finger!
Just to avoid any potentially dangerous confusion, it must be said that there are other species, unrelated and not all plants, commonly known as Dead Man’s (or Dead Men’s) Fingers, one of them deadly poisonous. Oenanthe crocata, a member of the carrot family (Apiaceae), is known under the common name ‘Hemlock Water-Dropwort’, but is also sometimes called ‘Dead Men’s Fingers’ (on account of the shape of its tubers). All parts of this plant are poisonous and occasionally lead to fatalities. Looking similar to Cow Parsley (Anthriscus sylvestris) or Comon Hogweed (Heracleum sphondylium), it should be hard to confuse Oenanthe crocata with Decaisnea insignis. However, since Oenanthe crocata is deemed one of the most poisonous plants in Britain, a word of warning seems appropriate here. After all, as my colleage Steve Davis pointed out, in recent years Kew has received frequent enquiries concerning Oenanthe crocata, including a case of someone being admitted to A&E, and several cases of livestock or pet poisonings. Other ‘Dead Man’s Fingers’ are Xylaria polymorpha (a fungus), Alcyonium digitatum (a species of soft coral) and Codium fragile (a seaweed).
5 comments on 'The Sweet Taste of a Dead Man’s Finger'
With people across the world already starving and the population growing by the minute there aren’t many issues which are more serious or more immediate. Gathered to discuss what the answers might be were: Dr Paul Smith and Professor Monique Simmonds from Kew, Dr Geoffrey Hawtin from the Global Crop Diversity Trust, Professor Charles Godfray from Oxford University and Judith Batchelar, Director of Sainsbury’s Brand. After an introduction from Kew’s Director, Richard Deverell, the task of orchestrating the debate fell to Quentin Cooper, the science journalist famous for BBC Radio 4’s 'Material World' and our chair for the evening.
Panel and audience in the Kohn Centre at the Royal Society (Photo: Andrew McRobb, RBG, Kew)
Charles Godfray started on a note of cautious optimism. Yes, the population is growing, but the rate of growth is slowing down. As people become more affluent they tend to have fewer children and, in general, the human population keeps itself under control. Charles noted that “our” diet – the diet of wealthy westerners as it is now – won’t be available for 10 billion people; that’s not realistic. But if we improve global governance and production systems to use the land we have more efficiently, then we will be able to feed everyone.
Geoff Hawtin echoed Charles’ optimism, noting that 50 years ago the population of India faced starvation and people thought their food production problems were insurmountable. Now the country is thriving and produces enough food to export it. The “Green Revolution” was a triumph and science has shown us how to produce food much more efficiently. The key challenges now are how we give people access to that food and how we ensure its quality.
Geoff noted that fostering genetic diversity is crucial to our success. For example, minor crops and crop wild relatives contain valuable traits which we need to preserve. Geoff highlighted the importance of Kew’s role in protecting and utilising this diversity before handing over to Paul Smith, head of Kew’s Millennium Seed Bank Partnership. Paul emphasised three things Kew can bring to the table: an unrivalled collection of plants and plant material; world-class expertise; and global partnerships.
Panellists: Judith Batchelar, Director of Sainsbury’s Brand; Dr Geoffrey Hawtin from the Global Crop Diversity Trust; Paul Smith, Head of Kew’s Millennium Seed Bank Partnership (Photo: Andrew McRobb, RBG, Kew)
Judith Batchelar then noted that Sainsbury’s currently feeds 24 million people a week – a small number, globally speaking, but one that means the supermarket chain needs a sound understanding of production and supply. Sainsbury’s is investing in research and development in a way that would have been unimaginable 5 years ago and is working with Kew to find sustainable sources, protect ecosystems and make better use of the genetic diversity available.
Finally Monique Simmonds, head of Kew’s Sustainable Uses of Plants Group, pointed out that food security is still a very new challenge. Kew has the expertise to identify quality food sources and ensure they have the traits we value most. This gives us the opportunity to improve food supply, food quality and food safety.
After this point the discussion ranged from agriculture to biotechnology, and from pollinators to population control, via GM crops and many other related issues. Quentin kept the panellists in order and steered the lively discussion with wit and verve. By the end everyone still had more they wanted to say and the conversations continued long after the panellists had left their seats. But the defining message was, yes, we can feed 10 billion people - but only if we seize the opportunities available to us and make the best use of the resources we have right now.
Kew Patrons and other guests enjoying refreshments after the debate (Photo: Andrew McRobb, RBG, Kew)
This event was part of the Kew Patrons calendar. The next debate will be at the Royal Geographic Society on 7 November and is titled 'The World's Most Valuable Bank.' Patrons also enjoy various exclusive social events such as an autumn drinks reception with senior Kew staff.
- Daniel Barker, Patrons Officer -
Become a Kew Patron
Kew Patrons provide invaluable support to Kew, funding our vital science and conservation work as well as helping maintain our cherished Gardens and iconic heritage buildings. If you would like to find out more about joining the Kew Patrons programme, please contact Daniel Barker.
Telephone: 020 8332 3238 (Mon - Fri 9am - 5pm)
0 comments on 'Feeding the ten billion'
"It would not, perhaps, be correct to say that the Durian is the best of all fruits, because it cannot supply the place of the subacid juicy kinds, such as the orange, grape, mango, and mangosteen, whose refreshing and cooling qualities are so wholesome and grateful; but as producing a food of the most exquisite flavour, it is unsurpassed."
[Alfred Russell Wallace, 'The Malay Archipelago', 1869]
Durians for sale at a market in Malaysia (Photo: Siew Hoon Lee)
The King of Fruits
If there are "100 things you should taste before you die", then the durian fruit is certainly in the top ten. Hailed as the undisputed ‘King of Fruits’ in southeast Asia, to westerners this exotic delicacy can be a real ‘Marmite test’: you either love it or you hate it! However, unlike Marmite, the durian’s contentious ambiguity does not lie in its taste, which is delicious, but rather in its disagreeable smell. To give you an idea, the experience of tasting your first durian can be compared to eating custard cream with a dash of Baileys in a men’s changing room crowded with steaming athletes returning from a heavy workout and a sumptuous dinner of raw onions and garlic. Hmm...
Understandably, this may have dampened your appetite for durian. So here’s some botany first, before we delve deeper into the culinary qualities of this most infamous of fruits and discover the true significance of its outrageous smell.
A durian fruit opened up to expose the large seeds wrapped in yellow juicy arils (Photo: Wolfgang Stuppy)
The southeast Asian genus Durio belongs to the Mallow family (Malvaceae) and comprises 20-30 species, at least eight of which are edible. The economically most important species of durian (Malay for “thorny fruit”), Durio zibethinus, has been cultivated in south-east Asia for centuries. Its large white nocturnal flowers are borne directly on the major branches (a phenomenon called ‘cauliflory’) which later have to be strong enough to carry the heavy fruits. The flowers reportedly smell like sour milk and are pollinated by bats which drink the copious nectar offered.
Flowers of Durio zibethinus (Photo: Bryan Brunner, Montoso Gardens, Puerto Rico)
Durians are so popular in southeast Asia that there are literally hundreds of different cultivars of Durio zibethinus. This is also the only species traded internationally. You can easily pick up a durian in London’s Chinatown if you are willing to pay around £20 for one. Alternatively, you can buy a few individual seeds on a Styrofoam tray covered with cling film. As for different flavours, I have only ever seen one single variety offered in Europe, which is usually imported from Thailand - the Mon Thong variety (Mon = pillow, Thong = gold).
Portions of durian seeds for sale in Malaysia (Photo: Siew Hoon Lee)
Size and growth
The durian’s highly-prized fruits can be the size of a football and weigh up to four kilograms. On the outside they are covered by a ferociously spiny, dull green to yellowish-brown husk (duri = Malay for thorn). Inside, the fruit is divided into 5 compartments representing the five carpels from which the fruit develops. When ripe, the heavy fruits drop off the branches and split slightly from the top down along 5 distinct, preformed lines which correspond to the median lines of the carpels. At this stage the fruits begin to emit their infamous ‘body odour’ that has been variously described as resembling a blend of sweat, faeces, unwashed socks or a mix of rotten garlic and onions.
Detail of the spiky outer husk of a durian (top) and (below) the tip of the fruit as it begins to split when it’s ripe (Photos: Wolfgang Stuppy)
Disliked by most Europeans and banned from the underground in Singapore, the durian is treasured by people all over Asia and revered as the veritable ‘King of Fruits’. What seems like a dubious admiration does not reflect a twisted olfactory preference, but a fondness for the extraordinarily delicious taste of what lies inside the malodorous pod. The people of southeast Asia don’t just enjoy the fresh fruits. Durians are used to make all kinds of mostly sweet treats like pastes, cakes, cookies, milk shakes, ice cream, chips, candies and lots more.
Southeast Asian delicacies made with durian, e.g. ice cream, cake, durian puff and candies (Photos: Siew Hoon Lee & Wolfgang Stuppy)
Wallace on durian
The edible part of the durian consists of the white or cream to golden-yellow arils (= seed appendages) covering several very large (c. 2 x 6 cm), chestnut-brown seeds. When the fruits are ripe, the hard tissue of the yellowish arils disintegrates into a custard-like cream whose consistency and flavour has been described as a tantalising mixture of nuts, spices, bananas, vanilla and onions. After his first visit to Borneo, the great 19th century naturalist Alfred Russell Wallace wrote:
The Durian grows on a large and lofty forest tree, somewhat resembling an elm in its general character, but with a more smooth and scaly bark. The fruit is round or slightly oval, about the size of a large cocoanut, of a green colour, and covered all over with short stout spines the bases of which touch each other, and are consequently somewhat hexagonal, while the points are very strong and sharp. It is so completely armed, that if the stalk is broken off it is a difficult matter to lift one from the ground. The outer rind is so thick and tough, that from whatever height it may fall it is never broken. From the base to the apex five very faint lines may be traced, over which the spines arch a little; these are the sutures of the carpels, and show where the fruit may be divided with a heavy knife and a strong hand. The five cells are satiny white within, and are each filled with an oval mass of cream-coloured pulp, imbedded in which are two or three seeds about the size of chestnuts. This pulp is the eatable part, and its consistency and flavour are indescribable. A rich butter-like custard highly flavoured with almonds gives the best general idea of it, but intermingled with it come wafts of flavour that call to mind cream-cheese, onion-sauce, brown sherry, and other incongruities. Then there is a rich glutinous smoothness in the pulp which nothing else possesses, but which adds to its delicacy. It is neither acid, nor sweet, nor juicy; yet one feels the want of none of these qualities, for it is perfect as it is. It produces no nausea or other bad effect, and the more you eat of it the less you feel inclined to stop. In fact to eat Durians is a new sensation, worth a voyage to the East to experience.." [Alfred Russell Wallace 1869: 'The Malay Archipelago']
As much as the people of southeast Asia love durians, because of the smell they leave behind it is forbidden to carry them on the underground in Singapore (Photo: Siew Hoon Lee)
Bad smell and seed dispersal
Believe you me, if you have never tried a durian before, you will never have tasted anything so amazingly rich and complex in your life. I absolutely love durian, but I have seen fellow Europeans unable to share my enthusiasm because they simply could not overcome the unsavoury associations conjured up by the durian’s bad smell. As a scientist, I am looking for a logical explanation which helps me to understand the durian’s offensive stench. It is pretty obvious that it all boils down to the durian’s strategy of getting its seeds dispersed.
The durian’s dull green to brownish colour and odour strongly suggest that the fruit is adapted to be dispersed by mammals. Most mammals are colour-blind or have just dichromatic vision but a very keen sense of smell. They rely much more on their noses than their eyes to find food or sense approaching predators.
Weirdly, heavy, sickly and sometimes yeasty scents with olfactory components of fermenting fruit and ‘mammalian body odour’, which we humans find repulsive, are very attractive to many (other) mammals. What’s more, the fact that the durian drops to the ground when ripe, combined with its large size, heavy weight and tough husk indicate that only large terrestrial animals with a mouth big enough to swallow the bulky seeds and sufficiently strong and dexterous to break open the spiky armour are invited to the meal.
Only larger animals have the strength to break through the spiky husk of a durian (Photo: Wolfgang Stuppy)
Seed dispersers and pulp thieves
It is therefore not surprising that a durian that has landed on the ground and begun to emit its more than recognizable smell attracts a variety of big beasts including elephants, Asian rhinos, orangutans, gibbons, monkeys (e.g. long-tailed macaques), tapirs, wild boar, deer and even carnivores like tigers, leopards, civets and sun bears. Any remains of the durian left by these big animals are scoured by smaller durian-lovers ranging from squirrels to beetles and ants. Naturally, such a rich and delicious treat like the durian attracts a lot of attention, both from genuine bona fide seed dispersers, the durian’s actual ‘target customers’, as well as from pulp thieves. The latter indulge in the nutritious pulp but actually do not help to disperse the seeds and sometimes even destroy them in which case they become seed predators.
Ideal dispersers either carry the seeds over a significant distance (e.g. 20 m or so) and discard them undamaged after eating off the aril (e.g. long-tailed macaques) or they swallow the seeds whole and defecate them intact (e.g. elephants, rhinos). Pulp thieves, on the other hand, would eat the pulp but then fail to transport the seeds (e.g. sun bears). It is not easy to find reliable scientific information about the dispersal ecology of durian. However, during one very interesting field study carried out in Sabah, Malaysia long-tailed macaques turned out to be the most efficient bona fide disperser of the seeds of Durio zibethinus.
A single seed inside a durian, still wrapped in the delicious yellow aril (Photo: Wolfgang Stuppy)
Pygmy elephants and orang utans
Although elephants are known to eat durians and pygmy elephants (Elephas maximus borneensis) were present in the study area, they were not observed to help with dispersal. Sumatran rhinos (Dicerorhinus sumatrensis), also very likely to be native bona fide dispersers in Sabah, were absent from the study area. Most surprisingly, orang utans, long known to be avid consumers of durians and generally deemed to be among its primary dispersers, turned out to be mere seed predators. The apes pluck immature durians and eat both aril and seeds, leaving only the seed coats which they spit out after their meal.
Orang Utan (Pongo pygmaeus) in Borneo eating a durian (Copyright © Konrad Wothe; www.konrad-wothe.de)
This is somewhat surprising because with their flimsy brown seed coats, durian seeds rely on chemical rather than physical protection (see my post about the ice-cream bean) in the form of toxic fatty acids (e.g. sterculic and malvalic acids) present in the tissue of the storage embryo. Perhaps orang utans have developed some kind of immunity or their bodies simply tolerate higher doses of these toxins than other animals. Toxins aside, durian seeds are highly nutritious, consisting of nearly 50% carbohydrates with little protein and fat. Boiling or roasting turns them into an edible starchy treat, a source of food long used by native peoples.
Another study showed that although tapirs eat durians and could therefore act as bona fide dispersers, the seeds fail to germinate after passing through the animal’s gut.
I am very grateful to my Singaporean friends Siew Hoon Lee and Hong Ling Lim for taking lots of photos of all things durian for this blog. Many thanks also to Konrad Wothe (www.konrad-wothe.de) for his kind permission to use his photograph of an Orang Utan eating a durian, and to Bryan Brunner from Montoso Gardens in Puerto Rico for allowing us to use his photograph of the flowers of Durio zibethinus.
- Wolfgang Stuppy -
P.S.: I am not quite sure how but, allegedly, durian acts as an aphrodisiac. As a Malay saying goes: "When the durians fall down, the sarongs fly up!"
- Further information on Botanical terminology
- Artist Marianne North recounts life in Singapore including the 'Darling Durian'
- Kew Fund: Chocolate, Rainforests and Conservation - find out how Kew's work is helping to protect species like the Durian
7 comments on 'Durian - the king of fruit'
Keep up to date with events and news from Kew
The Millennium Seed Bank Partnership works with over 80 countries worldwide as we work towards our current goal of collecting and storing seeds from 25% of the world's wild plant species. To complete such a target requires a wide range of skills and expertise including training, research, seed processing, database management and fundraising.
Follow Kew on twitter
- around the world
- the UK
- at risk
- ground breaking
- needs help
- english heritage
- Kew overseas
- verge of extinction
- wet tropics
- gifts that help
- South East Asia
- of use
- hot spot
- english garden