Millennium Seed Bank blog

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)

Acknowledgements
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.  

-Wolfgang-
 

P.S.

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!

Related links

• 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

Merry Christmas!

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) 

Really?

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 -

Related links

• Visit Wakehurst for some 'Christmasy' activites
• If you think it's cold outside, try being inside the Seed Vault at the Millennium Seed Bank!
• Want to know more about the plant you don't want to find yourself under at Christmas?

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

Strange flavours

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. 

Amazonian superfood

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.

- Wolfgang - 

Related links

• Beyond the Gardens: The Millennium Seed Bank Partnership - A short film showcasing behind the scenes work of Kew's scientists
• Kew's Projects in Brazil
• Loving Wolfgang's blogs? Discover more from his awesome books ...

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 -
 

Related links

• 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

Ever since I can remember I have been fascinated by plants, especially all things edible that come from them. And the more exotic the plant, the better! After blogging about the cashew nuts, a very well-known exotic treat, I decided to now choose a seedy delicacy that is less well-known, at least in our temperate climate.  

Sweet seeds

The legume family (Leguminosae or Fabaceae) is an amazingly diverse (nearly 20,000 species worldwide!) and incredibly useful group of plants. They feed us with beans, peas, lentils, soya and loads of other pulses and they treat us with delicious peanuts, tamarinds and liquorice. When travelling to far-away tropical countries, we are likely to encounter lesser spotted members of this miraculous family and some of them bear strange-looking but excitingly delicious fruits. One of these scrumptious exotics is the South American ice cream bean, Inga edulis, locally called ‘guaba’ (pronounced ‘wuba’). Behind this mouth-watering name lies a beautiful tree with a remarkable fruit.

 Fruit of the ice cream bean tree (Inga edulis, Leguminosae) photographed in its native Brazil 

A two metre long candy bar!

Reaching a height of up to 30m (96ft), an ice cream bean tree produces cylindrical and often spirally twisted bean-like pods that grow up to more than two metres(!) in length. This is no hoax! One of my colleagues at Kew, Dr. Terry Pennington, is a specialist on the genus Inga. Whilst discussing this blog with him, he told me that he was supervising Inga trials in Amazonian Peru in the early 90’s, they had a competition on the local radio to find the longest ice cream bean. The winner brought one which measured 2.07 m long.

Inside, lined up in one row, the pods contain numerous large purple-black seeds embedded in an edible, translucent-white pulp. The sweet flavour of the spongy pulp resembles that of vanilla ice cream, hence the name. Basically a yard-long candy bar that grows on a tree, most people will be sufficiently impressed by the size of this fruit and its delicious flavour. As a practicing ‘seed nerd’, however, I find something else quite extraordinary, too. 

Inside an ice cream bean lie the juicy delicious seeds

Seeds of Inga edulis with and without their white fleshy seed coat. What is left after the white juicy part has been eaten is the bare naked embryo

Unlike most fleshy fruits, the sweet pulp of the ice cream bean is not produced by the fruit wall but by the seed itself. Usually, seeds are covered by a hard seed coat to protect the precious embryo inside against both the elements and hoards of seed-eating critters. In the ice cream bean, however, the entire seed coat becomes soft and fleshy. Once you have nibbled a hole in it at one end, you can basically strip it off like a sock and suck the sugary treat! What remains is the purple-black embryo. Although it looks very dark on the outside, underneath its black skin, the embryo is actually green.

Cross section of the embryo of an ice cream bean (Inga feuillei, see below) showing that underneath its dark purple skin the embryo is actually green.

The genus Inga contains about 300 species of shrubs and trees, all native to the warm and tropical parts of the Americas (including the Antilles) and most of them occurring in the Amazon rainforest. Although Inga edulis (edulis meaning ‘edible’) is the most common species that is referred to as ‘ice cream bean’, there are a number of other Inga species that spoil us with equally delicious fruits, for example Inga feuillei (called ‘pacay’ in Peru), I. rhynchocalyx, and I. spectabilis. Their fruits differ in shape and size but inside they are very similar.

Because of their delicious taste, ice cream beans are very popular in many parts of Central and South America, where they are almost always eaten raw. During the tropical wet season when fruits are abundant, monkeys and birds feast on the sweet pulp and scatter the soft embryos.

But aside from their edible fruits, Inga trees are also useful in other respects. Like many members of the legume family, Inga trees have the ability to fix nitrogen with the help of Rhizobium bacteria which they house in specialized root nodules. Because they introduce nitrogen from the air into the soil, these root nodules act like fertilizer and help to improve soil fertility. Moreover, Inga trees have long been grown by indigenous Amazonians for food, shade and timber and they have also proven very useful as shade trees in cacao, coffee, tea, black pepper and vanilla plantations.

Another delicious ice cream bean: Inga rhynchocalyx, a native of the Amazon rainforest

But it’s not only the fruits that make Inga trees so very special. Their flowers, which produce the delicious ice cream beans, are pretty amazing too. They only open for one night and wither very quickly in the early morning. Like many other nocturnal flowers, they are large, white in colour and arranged in dense clusters (inflorescences). The individual flowers consist mainly of a brush-like tuft of stamens with long filaments. Flowers of this type are typically pollinated by bats. Their furry faces get powdered with pollen as they search for nectar at the base of the flower. Recent research into Inga has shown that at least in some species (e.g. Inga sessilis), hummingbirds are the first visitors just after the flowers open, followed by bats as well as hawkmoths throughout the night.

The nocturnal, brush-like flowers of Inga rhynchocalyx only last for one night and are mainly pollinated by bats 

One last thing...

In my blog post on the cashew nut I was raving about eating embryos and how delicious they are. Those of you who read this blog might wonder as to why the birds and monkeys that feast on ice cream beans don’t also eat the embryos wrapped inside the juicy seed coat. Good question indeed since hungry animals usually devour everything they find palatable and digestible. The answer to this is not only a fascinating example of the co-evolution between plants and animals but also a lively illustration of how plants pursue different strategies to achieve the same goal: in seeds it’s all about the safe dispersal of their embryos.
 

Why would animals only eat the fleshy seed coat and not the large soft embryo (here cut in half) inside?

When it comes to protecting their seeds, animal-dispersed fruits that offer edible rewards to attract animal dispersers have two options to increase the chances of their seeds to escape destructive mastication: mechanical or chemical protection. Plainly this means that either seeds are encased in a really hard shell (see my blog on the Texas mountain laurel) or they are laced with bitter-tasting substances (usually tannins) and/or poisonous chemicals that teach uninitiated animals enjoying a particular fruit for the first time a lesson they won’t soon forget. If you need experimental evidence for this, try chewing the seeds of grapes, apples, oranges, avocados or papayas. In the unlikely event that you actually enjoy the experience, please do note that the seeds of apples and other members of the rose family (e.g. plums, apricots and bitter almonds) contain highly toxic cyanide (actually a cyanogenic glycoside called amygdalin, to be precise). But fear not! You are unlikely to have sufficient apple seeds at your disposal to actually poison yourself. For example, one kg of Fuji apple seeds contain the equivalent of c. 700-800 mg hydrocyanic acid (see this article from Food Chemistry for more information). When ingested, the lethal dose is about 50 mg of cyanide (depending on your body weight) so you would have to eat about 60-70 g of fresh apple seeds. That doesn’t sound like a lot but how many seeds is that? Since I couldn’t find any reliable figures for the weight of an average apple seed, I chopped up my Braeburn that I bring for lunch every day. I found three seeds in it that weighed 211 mg altogether, so that’s 70 mg per seed. To get to the potentially ‘lethal dose’ of 70 grams of seeds I would need 1,000 apple seeds. My cherished lunchtime Braeburn yielded only three fully developed seeds so I would need over 300 more Braeburns before I could contemplate to seriously poison myself. Hmh...

Returning to the actual matter of this blog, in the case of the ice cream bean this means that in the absence of even the slightest mechanical protection, the embryo is almost without doubt (I haven’t tried it!) very bad-tasting, usually bitter, if not actually poisonous.

- Wolfgang -

 All photographs by Wolfgang Stuppy

Related links

• Growing legumes of your own? Start saving your seeds for The Great Seed Swap at Wakehurst Place!
• Kew's projects in Peru
• Are you making the right consumer choice when it comes to soya products?