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.
Known as 'castor beans', the seeds of Ricinus communis, a member of the spurge family (Euphorbiaceae), are among the most infamous seeds in the world. This blog is about their beauty, morphology and notoriety.
Seeds of Ricinus communis, commonly also called ‘castor beans’ (Photo: W. Stuppy)
Being the only species of the genus, Ricinus communis is a pretty unique plant, and this holds true for many reasons, as you will discover. Botanically, it belongs to the spurge family (Euphorbiaceae) which means it’s closest relatives include economically important plants such as the Para rubber tree (Hevea brasiliensis) and cassava (Manihot esculenta) as well as popular ornamentals such as poinsettia (Euphorbia pulcherrima) and crown-of-thorns (Euphorbia milii).
The castor oil plant (top; Photo: A. McRobb) and four of its relatives in the Euphorbiaceae family (below; Photos: W. Stuppy). The smaller photos show flowers of poinsettia (top left), cassava (top right), crown-of-thorns (bottom right) and a rubber tree tapped for its latex (bottom left)
Originally native to East and Northeast Africa and the Middle East, the castor oil plant (Ricinus communis) has spread throughout the tropics and has even become an invasive pest in places like Hawaii, South Africa, Australia and the Galapagos Islands. A fast growing tropical shrub that can reach a height of up to 5 m or more, it cannot survive our cold winters. Nevertheless, because of its striking large leaves and bold architectural ‘Gestalt’, Ricinus is a popular garden ornamental in temperate climates. It even comes in a range of different garden cultivars, for example ‘New Zealand Purple’ with dark red leaves.
Young fruits of a purple and a green variety of Ricinus communis (Photos: A. McRobb, left, and W. Stuppy, right)
Easily beating competition from the rather unspectacular wind-pollinated flowers, the most beautiful, interesting, useful and scariest part of the castor oil plant are its seeds, also called ‘castor beans’ (although they have nothing to do with real beans). They come in sets of three enclosed in soft-spiny capsules. The fruits add to the decorative looks of the plant but they eventually dry up as they ripen and explode to scatter their highly characteristic seeds. A distinctive feature of Ricinus communis, its seeds are smooth, shiny and mottled in various shades ranging from white over beige, brown and maroon to grey and black. Just as every zebra has a unique pattern of stripes, no two castor beans ever share the exact same seed coat pattern. The mottling provides the seeds with camouflage against mice and other seed eating animals as they lie on the ground after their explosive expulsion from the fruit. If lucky, they only need their camouflage for a short while as a rescue team of little helpers should soon be on the way...
Zebras and castor beans: No two individuals ever show the same pattern in their coat (Photos: W. Stuppy)
Ticks, ants and a strange thing called an elaiosome
The seeds’ shape is rather similar to a tick (e.g. Ixodes spp.) and with 'ricinus' being the Latin word for 'tick', it is pretty obvious where the castor oil plant got its scientific name from. Resembling the small capitulum (comprising the head and mouth parts) at the front end of a tick, castor beans carry a yellowish-white nodule that acts as an elaiosome (‘oil body’) and attracts ants for dispersal. The ants, irresistibly drawn to the fatty nutritious elaiosome, carry the seeds into their underground nests. Here, rather than devouring the precious morsel themselves, they feed it to their larvae. After the elaiosome has been removed, the ants usually abandon the still viable seeds inside the nest or discard them outside the nest on the rich soil of the colony’s refuse piles. In doing so they provide a vital service to the castor oil plant: they help disperse its seeds in order for them to find a suitable place for germination.
Ants collecting the seed of a Cnidoscolus species, a close relative of Ricinus communis, in northern Mexico; note the white nodule (elaiosome) at the right end of the seed (Photo: W. Stuppy)
Others do it too!
The castor oil plant is not the only plant to call on ants to help with the dispersal of its seeds. Lots of other plants have seeds equipped with elaiosomes that pursue the same strategy. This includes many of the castor oil plant’s close relatives in the Euphorbiaceae family as well as other species from across the plant kingdom such as members of the legume family (most notably Australian wattles, i.e. Acacia spp., Leguminosae), milkworts (Polygala spp., Polygalaceae), snowdrops (Galanthus nivalis, Amaryllidaceae), violets (Viola spp., Violaceae), greater celandine (Chelidonium majus, Papaveraceae), and some cacti (Cactaceae).
Collection of SciArt images of ant-dispersed seeds; clockwise from bottom left: greater celandine (Chelidonium majus, Papaveraceae), Lake Logue wattle (Acacia vittata, Leguminosae), sand milkwort (Polygala arenaria, Polygalaceae), sun spurge (Euphorbia helioscopia, Euphorbiaceae), Blossfeldia liliputana (Cactaceae); centre: aztec cactus (Aztekium ritteri, Cactaceae)
[Images from ’SEEDS – Time Capsules of Life’ by Rob Kesseler & Wolfgang Stuppy and ‘FRUIT – Edible, Inedible, Incredible’ by Wolfgang Stuppy & Rob Kesseler; Copyright Papadakis Publisher, Newbury, UK]
The miracle of co-evolution
This close association of seeds and ants is called ‘myrmecochory’, which literally means ‘ant dispersal' (Greek: myrmêx, myrmêkos= ant; khôreô/chorein = to move, to disperse, to wander). Myrmecochory is a beautiful example of how plants and animals have co-evolved to form mutually beneficial relationships: the ant is given a nutritious and reliable source of food while the plant's seeds are dispersed far enough to reduce competition between the seedlings and their parent. By burying the seeds a short distance below the soil surface, the ants not only hide the seeds from predators like mice and other rodents, they also prevent them from being destroyed by fire. The latter may explain the important role ants play as seed dispersers in the dry habitats of Australia and Africa which are swept by seasonal wild fires.
Seeds of snowdrop (Galanthus nivalis, Amaryllidaceae) with a hook-shaped elaiosome at the bottom end of the seed (Photo: W. Stuppy)
A bit of seed morphology
Being a seed morphologist, I have to perform an ‘autopsy’ on the seeds of Ricinus to see what’s inside. Although castor beans may vary in size depending on their provenance, they are typically around 12 mm long. Underneath the brittle seed coat lies a soft, oily nutritious tissue called ‘endosperm’ into which the embryo (i.e. the baby plant) with its short axis and large but very thin and flat cotyledons (i.e. the first pair of leaves) is embedded.
Longitudinal (top) and cross section (below) of a castor bean; the embryo with its short axis and large, flat cotyledons (seed leaves) is embedded in copious oily endosperm (Photo: G. Toothill)
Castor oil – natural remedy or tool of punishment?
The oil that is stored in the endosperm of castor beans is meant to provide the embryo with energy during its germination. However, at least 6,000 years ago in ancient Egypt, humans had already discovered the usefulness of castor seed oil and took Ricinus communis into cultivation. Since these ancient times until the present day, ‘castor oil’ is used as a lubricating laxative to relief constipation. Taken in moderation, castor oil does just that but an overdose will inflict explosive diarrhoea. Accompanied by painful cramps, the latter can last for hours, causing unpredictable involuntary bowel movements of considerable magnitude even during sleep. Most people know about the effects of castor oil which is why it makes a very funny joke when Tom the cat (as in the cartoon ‘Tom and Jerry’) is threatened with a bottle of castor oil by his owner Nancy, should he not stay in his bed. As a child, I found this hilarious. [I still find it hilariously funny!]
Bottles of castor oil in Kew’s Economic Botany Collection (Photo: M. Nesbitt)
Death by diarrhoea
In real life overdosing on castor oil is no laughing matter. For example, force-feeding castor oil to prisoners was used as a means of torture by the Nationalists under the leadership of General Francisco Franco during the Spanish Civil War (1936-1939). Likewise, in Benito Mussolini’s fascist Italy (1930-1943) the paramilitary Blackshirts used castor oil for the very same purpose to deal with opponents of the regime. The severe diarrhoea brought on by the ingestion of large amounts of castor oil led to dehydration which could ultimately cause death.
Beyond lubrication and death
Castor oil is a very valuable oil that is produced on an industrial scale (about 300,000-500,000 tons per year), most of it in India, China and Brazil. Apart from effecting a powerful acceleration of bowel movement, coincidence has it that castor oil also makes a great lubricant in jet and racing car engines. The brand name ‘Castrol’ proves that point and the high-performance engine oil ‘Castrol R40’ is even famed for the beautiful smell it bestows on car races. But the industrial applications of castor oil and its derivatives go far beyond lubrication. In fact, its versatility is almost boundless. Castor oil is used in the manufacturing of paints, dyes, adhesives, inks, soaps, cosmetics, chocolate, hydraulic brake fluids, plastics, waxes, varnishes, sealants and synthetic resins. A product of the latter kind has recently been used to seal the leaking rain gutters of the Millennium Seed Bank. In accordance with Kew’s environmental commitment, the original stainless steel gutters were first lined with a flexible reinforcement fleece made from recycled plastic bottles. The fleece was then saturated with a solvent-free water-proofing resin made from sustainably produced castor oil.
The rain gutter on the roof of the Kew’s Millennium Seed Bank lined with a resin based on castor oil (Photo: W. Stuppy)
The truly dark side of the castor bean
I don’t have a morbid obsession with death but the story of the castor bean would be incomplete without revealing the pretty seed’s most lethal property. As if its potential to inflict death by violent diarrhoea was not enough, the castor bean contains yet another, much more potent substance, the tiniest amount of which can kill man, beast and bug. Notoriously famous for all the wrong reasons, ‘ricin’, as the toxin is called, ranks among the most poisonous substances found in nature, alongside abrin which is found in the seeds of the crab’s eye (Abrus precatorius, Leguminosae). Both ricin and abrin are glycoproteins (= proteins coupled with sugars) that kill individual animal cells by blocking their ribosomes. The latter are the cells' protein 'factories'. By knocking them out, ricin and abrin act like a spanner thrown into the works of the cell. Cell death leads to tissue necrosis which in turn can lead to organ failure and ultimately death.
The crab’s eye (Abrus precatorius, Leguminosae) is even deadlier than the castor bean (Ricinus communis, Euphorbiaceae) (Photos: W. Stuppy)
Don’t try this at home!
Lab experiments with human cell cultures have shown that penetration of just a single molecule of ricin into the cytoplasm of a cell is lethal. This explains the extreme toxicity of ricin. It is understandably difficult to carry out scientific experiments in order to establish the exact dose that is required to kill a human being. However, according to a report by the Federation of American Scientists entitled ‘Ricin: Technical Background and Potential Role in Terrorism’, the lethal dosage of ricin is as low as 3 to 5 micrograms per kilogram body weight if inhaled or injected. Uptake of ricin through the gastrointestinal tract is less effective so the lethal dose for ingestion is higher, something around 20-30 mg per kilogram body weight. In absolute terms this means that between 3-8 (some suggest up to 20) seeds chewed and swallowed are needed to kill a human.
Die hard – or how many beans kill a horse?
Reports about the toxicity of castor beans vary widely as to the number of seeds required to induce death. According to a 2004 report of the Centre for Food Security and Public Health at Iowa State University, among domestic livestock, horses are the most sensitive to ricin and can die from the ingestion of 4-7 seeds. Chickens and ducks are much more resistant and can allegedly take up to 80 seeds before they are knocked out. However, following the death of several thousand wild ducks due to castor bean poisoning in the Texas panhandle between 1969-1971, a scientific study from 1981 found that the LD50 (i.e. the dose that kills 50% of the ‘contestants’ participating in the experiment) for mallards (Anas platyrhynchos) appears to be just 3-4 seeds. Likewise, other sources claim that it takes at least 60 seeds to kill a horse. These wildly differing results could at least partly be due to variations in the quantity of ricin present in various strains of castor beans.
4-7 castor beans are allegedly enough to kill a pig (Photo: W. Stuppy)
Murder à la James Bond
Probably the most famous murder victim to be killed with ricin was Georgi Markov, a dissident Bulgarian writer who, at the time of his death in 1978, lived in London working for the BBC World Service. A prominent critic of the then communist regime in Bulgaria, Markov was assassinated in true James Bond-style. Whilst waiting at a bus stop on Waterloo Bridge, he suddenly felt a sharp sting in his right thigh and noticed a man speedily walking away holding an umbrella. Three days later Markov died at a hospital, aged just 49. A thorough autopsy revealed that Markov was shot with a tiny (1.7 mm) platinum pellet that had an x-shaped cavity filled with ricin. The sophisticated gun needed to launch the tiny pellet was built into the umbrella carried by the assassin, very much like one of ‘Q’s gadgets. Sadly, Markov must have died a very painful death. A lethal amount of ricin injected directly into the bloodstream causes severe internal bleeding followed by organ failure and death after 3-5 days of suffering.
One last thing...
Ardent consumers of castor oil need not worry about ricin. It is only soluble in water and not in oil. This means that the toxin will remain in the press cake and not cross over into the oil during the extraction process. By the way, ‘castor’ is Latin for ‘beaver’. Not that Ricinus communis has got anything to do with beavers. The name is a reminder of ‘castoreum’, an oily secretion from the beaver’s abdominal ‘castor sacs’. Combined with the beaver’s urine the animal uses castoreum to mark its territory. Since ancient Greece the aromatic smelling castoreum was used both as an aphrodisiac (perfume) and medicinally, for example, as a laxative. In the mid eighteenth century the oil from the seeds of Ricinus was (re-)discovered to be a much better laxative than castoreum. Thenceforth, the name was transferred, purely for reasons of pharmaceutical marketing. Today castoreum (‘beaver juice’) is still used in perfumes, cigarettes, candies and ice cream. Yum!
I want to thank my colleague John Adams who provided me the inspiration for this blog. Thanks to the industrial qualities of castor oil, as John pointed out to me, we will no longer have to put buckets under the few leaks in the corridors of the Millennium Seed Bank when it’s raining. Three other colleagues also very kindly contributed: Gemma Toothill took on the perilous task of cutting open and photographing the seeds of Ricinus communis, Mark Nesbitt specifically photographed some of the castor oil bottles in our Economic Botany Collections, and Andrew McRobb lent me some of his Ricinus photos.
5 comments on 'Ants, constipation, murder and the seeds of Ricinus communis'
Being a great fan of weird and wonderful food plants, I want to start this year’s round of blogs about interesting fruits and seeds with an enigmatic vegetable. It is called the ‘snake gourd’ or, if you prefer Latin, Trichosanthes cucumerina var. anguina. Probably originally domesticated in India, the wild form of the species (Trichosanthes cucumerina var. cucumerina) is native to southern and eastern Asia as well as to Australia and the islands of the western Pacific. Nowadays, snake gourds are also cultivated as a minor vegetable in parts of Africa, Madagascar and other tropical and subtropical regions.
Snake gourds grown in a greenhouse in China (Photo: Jie Cai)
As always, size does matter
Like other gourds, the snake gourd is a member of the pumpkin family (Cucurbitaceae) and has seeds similar to its cousin the water melon (Citrullus lanatus), although slightly more eccentric, sporting a jagged-wavy outline. Far more curious than its seeds are the snake gourd’s fruits. As the name implies, they are very (!) long, slender and often wriggly like a snake. The fruits can easily reach 1.5 m in length and in 2010 someone in Oman claimed to have grown the longest snake gourdever at 1.88 m.
Top: Seeds of snake gourd (Trichosanthes cucumerina). Below: seeds of water melon (Citrullus lanatus) (Photos: Gemma Toothill & Elly Vaes)
The longest gourd in the world
By the way, the officially longest gourd in the world was a ‘luffa’ (also ‘loofah’) or ‘sponge gourd’ (Luffa aegyptiaca; syn. L. cylindrica) grown in China in 2008 which measured 4.55 m. Imagine how many scrubbing bath sponges you could cut from that whopper loofah!
Like luffa gourds, snake gourds are eaten as a vegetable when very young, although they both taste rather bland. As snake gourds get older, their flesh becomes tougher and more bitter and their rind turns dark red and hardens. Curiously, fully mature snake gourds are tough enough to be turned into didgeridoos. Inside they contain a soft, red, tomato-like pulp that can be used as a tomato-substitute in cooking.
Left: loofah sponges for sale in a Shanghai market. Right: a loofah sponge as it can be bought in UK supermarkets. The ‘sponge’ consists of the hardened network of vascular bundles of the fruit of Luffa aegyptiaca or L. actangula (Photos: Wolfgang Stuppy)
Confessions of a Seed Morphologist
At this point I have a confession to make. I have actually never eaten a snake gourd in my life. Worse even, the reason that I write this blog is not because I find the fruit or the seed particularly ‘cool’. It’s actually the flower of the snake gourd that completely blew me away when I first saw it and so I decided to find a way to share my excitement with you (as a Seed Morphologist I am not really eligible to blog about flowers!).
A few years ago I grew a cucumber-like vine in my conservatory at home from a packet of seeds I purchased in Chinatown. Finally, when the first flower bud began to open in the early evening, I noticed that something strange was going on. In fact, the unfurling of the flower bud was so amazing to watch that I decided to spend the night in the conservatory together with my camera and tripod. By nature, botanists are easily excited when it comes to plants, but whether you are into plants or not, you have to admit that the following photographs show something truly breathtaking:
The miraculous unfurling of a snake gourd flower (Trichosanthes cucumerina) (Photos: Wolfgang Stuppy)
During the course of a night, the bud of a snake gourd slowly unfurls into a beautiful white and strongly scented flower fringed with long, lace-like tendrils. Their shape, colour and scent, as well as their nocturnal opening, clearly indicate that the snake gourd’s flowers are moth-pollinated. Graceful and delicate, yet highly ephemeral, the little beauty lasts for just a single night but to me this is one of the most remarkable flowers in the world, and it belongs to a vegetable!
The fully opened lace-like flower of a snake gourd (Trichosanthes cucumerina) (Photo: Wolfgang Stuppy)
I want to thank my friend and colleague, Jie Cai, from the Kunming Institute of Botany in Yunnan, China, for photographing the snake gourds growing in their glasshouses, specifically for this blog.
After publishing this post I was contacted by Adam Ismail Arbi from Botswana. Adam runs ‘Adams Apple’, a farm where he grows snake gourds and a wide range of other vegetables. After reading my blog, Adam kindly sent some pictures showing how he grows snake gourds commercially for the local market.
The snake gourds are grown in a 300 square metre polytunnel at ‘Adams Apple’
Snake gourds being cultivated in a 300 square metre polytunnel (Image: Adam Arbi)
A weight (a rock) is tied to the end of the snake gourd to ensure that the fruit grows in a straight shape rather than ‘wriggle’ around as it would normally do.
A row of snake gourds weighted by stones (Image: Adam Arbi)
Adam sells the fruit by weight. The gourds are not packed or wrapped, and sent to customers as they are.
Snake gourds from Adam's farm, wrapped and ready for market (Image: Adam Arbi)
The gourds are collected and wrapped by staff in Adam's warehouse. This fine specimen is being held by Malebogo, one of Adam's employees.
Impressively large snake gourd being held by Malebogo (Image: Adam Arbi)
Adam told me he’s been growing snake gourds for 5 years. His ambition is to grow the longest snake gourd ever!
Good luck, Adam, and many thanks!
- Learn more about the partnership between the MSBP and The Kunming Institute of Botany, Yunnan, China
- Germination difficulties of the watermelon seed
- Discover more about gourds
9 comments on 'Observations on a strange vegetable - the snake gourd'
Since this will be my last blog for 2012, here comes a heartfelt ‘Merry Christmas’ to everyone, with a festive photograph of a fruit that looks like a raspberry. It actually shows a close relative of the raspberry (Rubus idaeus and hybrids thereof) called Japanese wineberry (Rubus phoenicolasius).
Japanese wineberry (Rubus phoenicolasius). [Image from ‘FRUIT – Edible, Inedible, Incredible’ by Wolfgang Stuppy & Rob Kesseler; Copyright Papadakis Publisher, Newbury, UK]
A flesh-eating killer raspberry
Edible and tasty, although not as delicious as a real raspberry, this native of northern China, Korea and Japan is sold by nurseries in the UK and grown by some people in their gardens. Unlike a regular raspberry, the calyx surrounding the fruit of a Japanese wineberry, is covered in sticky glandular hairs, similar to those found in carnivorous plants such as sundews (Drosera spp.). This has led some people to assume that Rubus phoenicolasius might actually be a carnivorous raspberry. A flesh-eating killer-raspberry? Sensational!
The calyx that surrounds a Japanese wineberry (left) is covered in glandular hairs which are very similar to those of carnivorous sundews, Drosera capensis (right). (Photos: Wolfgang Stuppy)
Well, not quite. A thorough scientific investigation in 2009 (pdf) has busted this myth. Although the glandular hairs of a Japanese wineberry contain tannins that help ward off herbivores, the mucilage they secrete does not contain any digestive enzymes and neither are the hairs capable of taking up any potential solutes. The sticky hairs on the calyx are mainly there to protect the bud from insect predation but not to kill and devour any creatures - although very small insects may become trapped and die.
The making of ...
Returning to the actual picture of the fruit shown at the beginning, you will have noticed that this is not a straight ‘shot’ with a regular camera. In fact, the image is taken with a Scanning Electron Microscope (SEM), a very expensive device that uses an electron beam instead of light to scan and visualise objects.
One of Kew’s Scanning Electron Microscopes at the Jodrell Laboratory (photo: Wolfgang Stuppy)
The advantage of an electron beam is that it has a much shorter wavelength than light. As a consequence, the resulting image has much greater depth of field and resolution, giving it a hyper-realistic look. The only disadvantage is that an electron beam has no ‘colour’ and so the resulting image comes in black-and-white only. To ‘spice-up’ the very ‘sciency’ monochromatic appearance of SEM pictures, I have teamed up with artist Rob Kesseler. Our fruitful (excuse the pun) collaboration started in 2005 and since then we’ve done quite a few crazy things in the lab which no respectable scientist would ever do. One was shuffling a whole Japanese wineberry into the vacuum chamber of a Scanning Electron Microscope.
Our specimen of a Japanese wineberry covered in a fine layer of platinum as a preparation for observation in the Scanning Electron Microscope (photo: Wolfgang Stuppy)
A microscope, not a macroscope!
As its name implies, a Scanning Electron Microscope is an instrument with which to magnify very small things to make them visible. At a diameter of about 2 cm, a Japanese wineberry isn’t exactly something you need a microscope to look at. So when we decided that an SEM ‘photograph’ of this fruit would look very ‘cool’, it was no surprise to discover that it was far too big to fit into the SEM’s field of view. Determined to succeed, we were forced to take 56 individual images which Rob then had to painstakingly stitch together into one. The rest is history.
The beginning of the jigsaw-reconstruction of the Japanese wineberry from 56 individual SEM photographs (image: Wolfgang Stuppy & Rob Kesseler)
Many thanks to everyone who has followed my blog so far and for the encouraging feedback. I know now that although I am probably the only Seed Morphologist in the village, I am surely not the only person who believes that seeds are amazing!
The seed of Floscopa glomerata, a member of the spiderwort family (Commelinaceae) from Mali, dressed up as Santa Claus. [Seed image from ‘SEEDS – Time Capsules of Life’ by Rob Kesseler & Wolfgang Stuppy; Copyright Papadakis Publisher, Newbury, UK; Santa hat design: Gemma Toothill]
- Wolfgang -
6 comments on 'The 'Christmassy' killer raspberry'
I am a bit behind with my blog this month, having only just returned from a trip to Manaus (Brazil) where I taught one of my courses on the structural diversity of fruits and seeds. However, while there I encountered another pretty amazing fruit which is worth devoting a blog post to.
The Amazon is a great place to discover new exotic fruits... and the Tarzan way-of-life (image Wolfgang Stuppy)
When travelling to such far-flung places, one of my passions is to try all the available exotic fruits, most of which I have at least heard about before. However, when I got to Manaus for the first time, I was almost shocked to find I had never heard of cupuaçu (pronounced ‘coo poo asoo’) before. Everyone told me this is the most famous and original fruit of the Amazon basin. In fact, it is considered by both locals and non-local connoisseurs to be the ‘taste of the Amazon’ and in March 2008 it was even declared the national fruit of Brazil. Sure enough, I was burning to try this mysteriously delicious fruit and find out what it actually ‘is’, from a botanical point of view.
The fruit of a cupuaçu (Theobroma grandiflorum) growing in the Amazon (image Wolfgang Stuppy)
What’s chocolate got to do with it?
I was surprised to learn that cupuaçu (Theobroma grandiflorum) is a very close relative of cocoa (Theobroma cacao), the main ingredient in chocolate. Both plant species are indigenous trees of the Amazon rainforest and native tribes have used their fruits as a food source for centuries, if not millennia. The cupuaçu’s shared ancestry with cacao is clearly reflected in their very similar flowers and fruits, although at a height of just up to eight metres, cocoa is dwarfed by its cousin the cupuaçu, which can grow up to twenty metres tall. Incidentally, the flowers of cupuaçu are also much larger and more heavily built than those of cocoa.
Left: flower of cupuacu (Theobroma grandiflorum); right: flowers of cocoa (Theobroma cacao) - (image Wolfgang Stuppy)
These very interesting-looking flowers give rise to large pods with a thick and tough brown (cupuaçu) or yellow to orange (cocoa) rind. Although similar in length (15-35 cm), the fruits of cupuaçu are more plump (up to 16 cm in diameter) and weigh up to 2 kg whereas cocoa pods are more slender and weigh only around 500 g. Inside their hard shell the fruits contain a white or yellowish juicy lump which consists of numerous large seeds covered in soft, fleshy seed coats (similar to the ice cream bean I have blogged about previously).
Fruits of cocoa (Theobroma cacao) on the tree (left) and cut in half (right), revealing the fleshy seeds, one of which has already started germinating (image Wolfgang Stuppy)
What most chocolate eaters won’t know
Chocolate owes its heavenly taste to cocoa butter extracted from the fermented seeds (‘cocoa beans’) of Theobroma cacao. Unbeknown to most people outside South America, the seeds of Theobroma grandiflorum yield a fat very similar to cocoa butter that is also used to make a type of chocolate called ‘cupulate’. Another fact that most chocolate eaters are unaware of is that the soft seed-coat-derived pulp surrounding fresh ‘cocoa beans' is also edible and it tastes delicious, just like the pulp of cupuaçu. However, neither of the two tastes even remotely of chocolate. Disappointing as you may find this - wait until you read about the flavours these fruits yield as they unfold on our palates.
Dried cocoa ‘beans’ on display in a market stall in Mexico City
The pulp of cocoa pods has a fresh, sweet and sour taste that has variously been described as reminiscent of apple, lychee, mangosteen, banana, rambutan or soursop. This sounds pretty exciting, but to me cupuaçu has a far more exotic and unusual smell and taste. In fact, it doesn’t taste like anything else so it is really hard to explain its aroma, but I will try. The cupuaçu’s rich, voluminous flavour is sweet, sour and slightly tart at the same time, with a very pleasant but heavy, fruity component reminiscent of a mix of pear, banana and pineapple. On top of all this, almost like a blanket, lies a rather strong hint of something bizarre, almost artificial, that to me tastes like a mix of aniseed and wintergreen or perhaps the resinous aroma of mango skin. In short, it simply tastes like cupuaçu! Some people claim that cupuaçu also has a hint of chocolate but this seems more of a fantasy inspired by its close relationship to cacao.
The fresh pulp of cupuaçu is either eaten raw or turned into refreshing drinks, ice cream, pastries, candies, jams etc. Because of its high levels of antioxidants (with anti-ageing effects!) cupuaçu has been touted by some as the next Amazonian ‘superfood’ after the fruits of the açai palm (Euterpe oleracea, Arecaceae) and guaraná (i.e. the seeds of Paulinia cupana, Sapindaceae), both also from the Amazon region. The latter two have already caused some recent ‘health-food excitement’ in North America and Europe.
Left: seeds of guarana (Paullinia cupana) for sale at a market in Manaus. Right: fruits of Paullinia pinnata which look very similar to those of guarana (image Wolfgang Stuppy)
Some natural history ...
As exciting as the unusual flavours of tropical fruits are, far more exciting is to find out why these fruits have evolved these flavours in the first place. Soft and fleshy tissues in fruits are usually there to attract fruit-eating animals which, in exchange for food, help with seed dispersal. Co-adaptation to a certain group of dispersers is reflected in a distinct set (‘syndrome’) of fruit characteristics.
For example, the yellow- to orange-coloured fruits of Theobroma cacao are protected by a thick, tough rind that is typical of primate-dispersed fruits. In order to open the fruits to get to the sweet pulp, an animal must have a certain strength and dexterity, such as that of monkeys. Although monkeys avoid swallowing the soft, bitter-tasting seeds, they still disperse them. They remove the cohesive lump of up to fifty fleshy seeds from the cocoa pods, and then take their bounty to a safe place in the canopy where they nibble off the luscious pulp.
After birds and bats, primates like these Emperor tamarin monkeys (Saguinus imperator subgrisecens) from the Amazon basin are among the most important seed dispersers in rainforests (image Wolfgang Stuppy)
The story isn’t quite that simple with the harder and much heavier fruits of Theobroma grandiflorum. There is no doubt the fruits are adapted to be dispersed by a certain type of animal, albeit one with a very big mouth and perhaps a taste for the extraordinary. However, when trying to match the cupuaçu’s suite of functional traits against present-day dispersers in the Amazon rainforest, there is nothing that really fits.
The available animals are either too small to handle the heavy, hard-shelled fruit, or stuff like this is simply not part of their diet. The fascinating truth is that the cupuaçu’s texture, size, colour, taste and odour indicate that it is a typical ‘megafauna fruit’, adapted to be dispersed by the huge beasts that inhabited the Americas until the end of the last ice age, between 10,000-15,000 years ago. Among them were giant ground sloths, mastodons and gomphotheres (four-tusked elephant-like creatures). Like many other fruits in the Amazon rainforest, the cupuaçu really is a typical gomphothere fruit!
Top: horse cassia (Cassia grandis; Leguminosae; the white bar); left: tagua palm (Phytelephas macrocarpa; Arecaceae); middle: stinking toe (Hymenaea courbaril, Leguminosae); right: genipap (Genipa americana, Rubiaceae) (Image Wolfgang Stuppy)
Some more Amazonian megafauna fruits that used to be on the menu of the big beasts of the last ice age. Note the dull colours - large mammals are colour-blind!
For a more detailed explanation of the megafauna dispersal syndrome see my earlier blog about the Texas Mountain Laurel. To readers who have a special interest in fruits that are adapted for dispersal by extinct animals (‘anachronistic fruits’) I recommend the excellent paper by Guimarães et al (2008) which also discusses the cupuaçu.
Oh, one last thing....
Because of its low melting point, the fat (‘butter’) extracted from the seeds of both cupuaçu and cocoa is also used as a base for suppositories.
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This is not a regular ‘Seed of the Month’ blog post. Rather than writing about the seeds of a particular plant, I decided that this time, I want to share my ideas of the ‘bigger picture’ with you, which lays bare the ultimate reason why we, here at Kew’s Millennium Seed Bank, are so passionate about saving seeds from all over the world. The following ‘essay’ is about life on Earth, the future of mankind and the true relevance of seeds. And so here it goes...
Science, washing powder and beyond
When scientists are lost for words they create technical terms which help them to communicate with each other more easily and precisely. Most of these technical terms don’t ever percolate into the public domain. However, nowadays everybody talks about biodiversity - some still think it’s a new kind of washing powder. But behind this abstract word lies a meaning that goes far beyond that of washing powder, in fact, far beyond anything anyone can imagine.
A (very!) small selection of fruits and seeds from all over the world
[Images from ’SEEDS – Time Capsules of Life’ by Rob Kesseler & Wolfgang Stuppy and ‘FRUIT – Edible, Inedible, Incredible’ by Wolfgang Stuppy & Rob Kesseler; Copyright Papadakis Publisher, Newbury, UK]
All creatures great and small
‘Biodiversity’ refers to the cornucopia of all life forms on Earth, most of which are still unknown to us. Estimates range from 3 million to 100 million species. A smart scientific study from 2011claims to have calculated that there are altogether almost 9 million species of plants, animals, fungi, bacteria and so-called protists (= microscopic critters that are neither plants, animals, fungi or bacteria). Of all these, only about 1.2 million are known to science and formally described. As for the other 8 million or so species, we kind of know that about 6.5 million of them are animals (mostly very small ones) but we don’t yet know who they are.
A tiny sample of planet Earth’s ‘life forms’ - all photos Copyright 2012 Wolfgang Stuppy
Kingdom of plants
After animals, the second largest kingdom of life on Earth are plants. At about 300,000 to 450,000 species, there are a lot less of them than animals but that doesn’t mean that they are less important. Quite the contrary! Many of us love plants, due to their sheer omnipresence, most of us can’t but take them for granted. But when we stop and think for a moment, I mean really think, plants, even the scruffiest of weeds, are amazing. Actually, they are not only amazing, they are, in fact, our life support system.
Unlike animals, plants have the remarkable ability to use sunlight to make sugar from just water and carbon dioxide during a complicated process called ‘photosynthesis’. In doing so, they not only produce their own food but also feed – either directly or indirectly – literally all life on Earth. Furthermore, as a ‘waste product’ of photosynthesis, they produce the oxygen in our atmosphere. To put it simply, without plants we would neither be able to breathe nor eat.
Flooded forest (‘Igapo’) on the Urubu River, Amazonas – Photo: copyright 2012 Wolfgang Stuppy
What’s the point of biodiversity?
Good question. Why would we need so many species if we don’t even know most of them? Let me try to illustrate this point using a not too far-fetched allegory.
Imagine your continued existence depends on a complicated life support system which, should it fail, would mean that you are definitely going to die. Scary stuff! Now imagine that your life support system is a very large, robust and luxurious one, one that has built in a great deal of redundancy and backup systems. This means that if one or several parts fail or break, there are plenty of other parts which can make up for the failure without you even noticing. Phew! Not too much to worry about then. In fact, you can almost forget that you are on a life support system. After all, it’s so huge and so fail-safe that you might take it for granted as much as the sun that rises every morning. And because it’s so huge and apparently so fail-safe, you probably think it’s no harm to make it a bit smaller by getting rid of some parts. After all, by making it smaller you can create more room for other important things, such as growing food to feed your family or to earn money (preferably lots of it!). Now imagine this huge and ever so reliable life support system is not a metal box with loads of man-made parts inside but a living system that consists of all the plant species on Earth as well as all the other organisms which, although they also depend on plants, still play important regulatory roles.
A colourful grasshopper in the Amazon rainforest - Photo: copyright 2012 Wolfgang Stuppy
Welcome to reality!
If you manage to take this imaginary step you have actually crossed from my very simple allegory into real life. By turning ever more ‘wild’ places like tropical rainforests into ‘cultivated’ land for agriculture, mines, factories, housing and so on, to produce ever more stuff for ever more people, we are causing the extinction of countless species. This extermination of species – unintended or not - is equivalent to the dismantling of our life support system which we can now give a name. It is actually called ‘biodiversity’.
Although ‘biodiversity’ is very robust and can cope with severe losses, there comes a point when it begins to ‘malfunction’ and finally fail if too many parts are removed. Here's a good analogy: remove part after part from your car until it stops working. You will find that some parts will make hardly any difference if they are missing, others will be crucial for the running of the engine and the turning of the wheels. It is just that nature is far more complicated than even the most sophisticated car and there are no mechanics out there who know exactly how to fix it.
A slab with plant fossils on display at the Canterbury Museum in Christchurch, New Zealand. These specimens belong to a mix of flowering plants, podocarps (a kind of conifer) and cycads, and are about 100 million years old (Photo: Wolfgang Stuppy)
Species have always come and gone in the Earth’s history, as we can tell from all the million-year-old fossils of strange-looking animals and plants displayed in museums. Even though it is true that extinction is a natural process, the current rate of extinction is about 1,000 times greater than the natural rate and this is solely due to human activities. Compared to the alarming loss of species, climate change, although currently dominating the media, is only the bitter ‘icing on the cake’.
Climate Change is just the bitter icing on the cake (Photo: Wolfgang Stuppy; Cake design: Michelle Wibowo)
Forever is not for ever – or is it?
Extinction of a species is forever. Each species that disappears takes with it one elaborate piece of our vast and complicated life support system, which itself is the result of millions of years of evolution. Tragically, on top of this, the extinction of a species also affects many other species with which it has shared the same environment for thousands if not millions of years. The fossil record tells us that life on Earth has already experienced five global mass extinctions.
After each disaster the recovery of global biodiversity took between four and twenty million years. Four million years at least! Nobody can imagine such a vast amount of time! To illustrate the dimensions, modern humans like us, have existed for no longer than about two hundred thousand years. It is pretty clear that we can’t wait for biodiversity to restore itself. For us, the vast geological time spans involved in the evolution of life mean that with every species that we lose, we lose a part of our life support system – forever!
Seeds are miraculous! (Images from ’SEEDS – Time Capsules of Life’ by Rob Kesseler & Wolfgang Stuppy, Papadakis Publisher, Newbury)
Why saving seeds is more than just a good idea
At this point it is worth remembering that plants are the only solar-powered primary producers, and, as such, support literally all other life on Earth. Because of their crucial importance, one trait of plants almost seems like a miraculous gift to mankind: their ability to produce seeds.
Unlike animals, most plants (apart from algae, mosses, ferns and other spore plants) can survive extensive periods of unfavourable conditions in the form of seeds. As long as they are kept dry, seeds can hold a tiny plant safe and alive (albeit in a quiet, coma-like state) inside their hard shell for years, decades, centuries or even millennia.
A typical seed with the tiny green baby plant sheltered in its centre. This particular seed belongs to the South African gifboom ('poison tree'; Hyaenanche globosa, Picrodendraceae) (Photo: Elly Vaes)
The ability of seeds to survive for long periods of time in the dry state is their most astonishing and momentous quality. Above all, it holds the key to the survival of a species! And this is exactly what we, Kew’s Millennium Seed Bank Partnership, are capitalising on. Because of their small size and longevity, seeds provide an extremely efficient means of saving species from extinction. Rather than accepting the fact that we will lose thousands of unique species of plants in the years to come, we make every effort to collect their seeds now in order to ensure their survival in the future. Saving seeds is the best chance we have to enable us to re-build essential parts of our life support system, should it eventually begin to fail.
Collecting seeds of prickly pears (Opuntia sp.) for the Millennium Seed Bank Partnership in Mexico (Photo: Wolfgang Stuppy)
To date, the Millennium Seed Bank Partnership has managed to collect the seeds of 10% of all plant species (c. 32,000 species). Until 2020, we aim to collect the seeds of 25% (75,000 species) of the world’s plant species. If you agree that seed conservation is a good idea you can help us achieve our goal by adopting a seed for £25 or saving an plant species outright.
A ‘cool view’ of the cold storage at the Millennium Seed Bank (Photo: Wolfgang Stuppy)
- Wolfgang -
- August's 'Seed of the Month' blog post - scrumptious ice cream bean
- Millennium Seed Bank Partnership - find out more about our work
- Visit Kew's Millennium Seed Bank at Wakehurst
- Adopt a seed, save a species - how you can help
- Kew species profiles - search through hundreds of profiles of plants and fungi
- One in five plants are at risk of extinction - find out more about plants at risk
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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.
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