Millennium Seed Bank blog

Traveling with animals is surely the most successful dispersal strategy that plants have evolved. Some want their fruits and seeds to be swallowed so that they travel as stowaways in the gut of an animal, whereas others prefer to latch onto the outside of passers-by.

The puncture vine: flower with fruit below

Sticky hitchhikers

After a walk through the countryside we often find some ‘sticky hitchhikers’ on our socks and trousers. The means by which they manage to attach themselves is simple and consists of small hooks that readily become entangled with the fur of mammals or the tiny loops of thread in the fabric of clothes. It was the microscopic structure of these diaspores that in the 1950s inspired the Swiss electrical engineer George de Mestral to develop the hook and loop fastener that we nowadays all know under the name Velcro®(based on the French velour = velvet, and crochet = hook). The ‘Velcro’ means of seed attachment is the gentle version and one very tenacious but harmless example is our native 'stickywilly' - also known as cleavers (Galium aparine).  

Fruits of Galium aparine 

Other plants are less gentle and some are, in fact, rather sadistic when it comes to achieving the dispersal of their seeds.

Medieval weapons

One example, the so-called puncture-vine, is found in warmer parts of Europe where its diabolical insidiousness has earned the fruits of this little plant the name 'devil’s claw' or 'caltrop' (See Note:1 below for Wikipedia's definition of a caltrop).

 Puncture vine (Tribulus terrestris) fruits

The tribulation inflicted by the fruits on unwitting animals (and sometimes people) is even reflected in the plant’s scientific name (Tribulus terrestris). As the fruits of the puncture vine, a member of the Zygophyllaceae family, mature, they split into five ‘nutlets’. Each nutlet is armed with two large and several smaller spines. In whatever position the nutlets end up on the ground, some of their spines will always point upward, like a medieval caltrop, ready to penetrate the skin of an animal or even the soles of shoes. For example, on the Hungarian plains the prickly hitchhikers used to cause sheep farmers considerable trouble by inflicting suppurating wounds on their animals, which hampered their ability to walk.

Martynia annua mature fruit showing ferocious spines

Three mature fruits of Martynia annua showing their ferocious spines and with one fruit still with its soft green cover on it

Claws of the devil

Other ruthless and brutal examples of ‘devil’s claws’ occur in the dry tropical and subtropical semi-deserts, savannahs and grasslands of America, Africa and Madagascar. Like the fruit of the puncture vine, they bear sharply pointed spines, claws or horns which bury themselves into the flesh rather than gently ‘velcro-ing’ to the fur of animals.

The North American devil’s claws belong to species of the genus Proboscidea (esp. Proboscidea louisianica) and their smaller relative Martynia annua, and are both members of the Martyniaceae family.

Proboscidea louisianica mature fruit with its two sharp hooks widely spread ready to catch onto the hoof of an animal

In South America it is their carnivorous relatives in the genus Ibicella that produce very similar devil’s claws, or unicorn fruits as they are also called (e.g. Ibicella lutea). All of them have harmless looking green fruits which only reveal their true nature after their fleshy outer part has withered away. As the exposed endocarps dry out, their elongated beak splits down the middle to produce a pair of curved, sharply pointed, spurs turning the diaspore into a vicious contraption, poised to cling around the feet of hoofed animals and bore into their skin.

Grappling hooks

The old-world members of the sesame family (Pedaliaceae) honour their close relationship with the Martyniaceae by sharing the same ruthless concept of dispersal and produce even meaner traps. As the author can testify from his own experience, the fruits of the Malagasy genus Uncarina are undoubtedly the most tenacious fruits of all. With their radiating spines crowned by a pair of sharply pointed, recurved hooks, they not only rip into skin with great ease but are also impossible to untangle without using a secateur.

Uncarina species showing spines and hooks

The most infamous member of the sesame family is Harpagophytum procumbens, aptly called grappling hook, grapple plant or, like its New World relatives, devil’s claw. Used as mouse traps in Madagascar, the almost preposterously horrid looking woody pods can inflict gruesome wounds to animals with cleft hoofs or relatively soft soles.

Besides being cruel, plants can also be fraudsters, as you will find out in my next blog.

- Wolfgang-

All above images by Wolfgang Stuppy and copyright Board of Trustees, Royal Botanic Gardens, Kew

Note 1: A caltrop consists of four spines arranged to point to the four corners of a tetrahedron so that however it falls, it will sit on three of the spines with the fourth one pointing up in the air. Caltrops were first used as a means to slow down pursuers on horseback but later proved to also work on pneumatic tyres in the motorised age. Iron caltrops were used as early as 331 BC at Gaugamela according to Quintus Curtius (IV.13.36). They were known to the Romans as tribulus or sometimes as Murex ferreus, the latter meaning 'jagged iron'. (from Wikipedia)

Related Links

• Millennium Seed Bank partners in Botswana collect 'devil's claw'
• Image of devil's claw
• Understand the parts of fruits and seeds in Wolfgang's glossary (pdf) 

My name is Jean, and I have been a volunteer for the Millennium Seed Bank Partnership for three years, and a Friend of Kew for many more. I work at the Seed Bank one day a week cleaning seeds and doing germination tests. I thought the chance to tour the Jodrell laboratory was too good to miss.

On hearing of this tour, which was open to Friends of Kew, I immediately booked places for myself and my fellow volunteer Val (who has notched up some seven years’ service).

The Jodrell laboratories at Kew Gardens

Cytogenetics

The first stop on our tour was the Cytogenetics lab, where research is carried out into the chromosomal makeup of plants. It seems that there is a wide variation in the number of chromosomes in plants. A few plants have just two pairs of chromosomes (humans have 23) whereas others have many more. One plant (a fern) from India is reported to over a thousand chromosomes per cell.

DNA extracts and molecules

Next was the Molecular Lab. All the DNA extracts which Kew has produced are listed on a database available to all. In addition, the extracted samples are available to researchers all over the world, through the DNA Bank.

Another important area of research is in the identification of plant compounds that have medicinal potential. Some 70% of these are plant-derived even now, because they are either impossible or too costly to synthesise. A compound from the Madagascan periwinkle (Catharanthus roseus) has increased the survival rate in childhood leukemia from about 20% to more than 90% in little more than a decade, and there are many more beneficial compounds yet to be discovered.

Inside the Jodrell laboratory
 

Fungi

Finally, we visited the Fungarium, which used to be called a Mycology Herbarium or Fungus Herbarium. However fungi are not plants - indeed they are more closely related to animals than plants! The oldest specimens date back to 1730, and some were originally collected by Charles Darwin.

All in all I found this a fascinating behind-the-scenes tour, and an insight into the importance to the community as a whole of the work done at Kew.

- Jean -
 

Related links

• More about the Jodrell laboratory
• Become a volunteer   
• Find out more about seed processing at the Seed Bank
• Friends of Kew
• News - Merger creates largest Fungarium in the world at Kew
• Molecular systematics at Kew 

Despite carrying the responsibility for the survival of a species, some fruits and seeds don’t seem to function in their current natural environment. How can this be when evolution through natural selection has shaped them over millions of years? The answer is like something from an Arthur Conan Doyle novel...

Seed of the Month - Dermatophyllum secundiflorum

The hard-nosed scientists among you might have found my last blog on why the seeds of Ravenala madagascariensis are blue already somewhat hair-raising, given that there is no published direct scientific evidence, yet, to back up my story. Well, here comes another daring observation and the hard-evidence junkies among you had better fasten your seat belts.

Texas mountain laurel flowers (Photo by Betty Alex)

Boring fruits, flashy seeds

The Texas mountain laurel (Dermatophyllum secundiflorum, until recently called Sophora secundiflora or Calia secundiflora), is a shrub from the southwestern United States and Mexico. It has some rather boring looking, large brown fibrous-woody fruits (‘pods’) that neither get eaten by any creature nor ever open to release their seeds, and yet, they contain extremely hard, beautiful shiny red seeds which seem perfectly adapted to attract birds for dispersal, if only the birds could get to see them. It’s a fact of life that fruits must ‘make sense’ within their evolutionary background (i.e. achieve the dispersal of their seeds in their co-adapted environment), otherwise they would not exist. Therefore, I conclude that the indehiscent fruits (meaning the fruits do not split open) of the Texas mountain laurel are typical ‘megafauna’ fruits, i.e. fruits that are adapted for dispersal by large (greater than 50 kg) mammals.

Fruits of the Texas mountain laurel (Photo by Wolfgang Stuppy)

To the taste of big beasts

The biggest terrestrial animals alive today are the elephant, rhinoceros, hippopotamus and giraffe. It is therefore no coincidence that the megafauna dispersal syndrome is best expressed in Africa and Asia where these animals still occur. In fact, ruminants such as giraffes and antelopes and non-ruminants such as elephants and rhinos are among the most important seed dispersers in the African savannah.

The fruits of many legumes are specifically adapted to attract these animals in that they are large, indehiscent, with a brown, leathery husk and often with a distinct smell that attracts even cattle. Since herbivores (plant eaters) are colour-blind, the brown fruits are visually inconspicuous but rich in digestible carbohydrates and protein; they contain extremely hard, smooth seeds that can withstand the grinding of strong molars. The fruits can remain on the tree but are often dropped to the ground as soon as they are ripe to provide easy access for their large terrestrial dispersers.

Seeds of the Texas mountain laurel (Photo by Wolfgang Stuppy)

This description pretty much matches the fruits of the Texas mountain laurel which happens to also be a legume. The only problem is that North America hasn’t really got much of a megafauna other than, for example, the native pronghorn and introduced cattle and horses.

Pronghorn in Texas (Photo by Wolfgang Stuppy)

Seeds from a lost world

However, until 13,000 years ago, towards the end of the Pleistocene epoch (1.8 million to 11,550 years ago) when the last Ice Age drew to a close, North America boasted a megafauna far richer than Africa’s today. The ancient menagerie of potential megafauna seed dispersers featured several species of native wild horses, camels and tapirs alongside fantastic creatures such as gomphotheres (four-tusked elephant-like creatures), mastodons and woolly mammoths weighing up to ten tons, giant ground sloths, the largest the size of a modern elephant, glyptodonts (giant armadillo-relatives the size of a small car), giant short-faced bears nearly twice the size of a grizzly, giant bisons, giant peccaries, giant beavers and giant tortoises. By the way, the pronghorn is a relic of this ancient megafauna.

'Megafauna' (Photos by Wolfgang Stuppy)

 
Returning to the fruits of the Texas Mountain Laurel, having no takers among the animals around today, I suggest that they are adapted to be eaten by one or several members of North America’s extinct megafauna. The rock-hard, shiny red seeds then stuck out from these animals’ dung piles where birds could spot them.

Looks juicy but.....

Red seeds of the Texas mountain laurel (Photo by Ellen Woods)

This is somewhat unsavoury, but mistaking them for something like a juicy red berry, at least some inexperienced birds would be tempted to pick up the seeds and fly away with them to a safer place (e.g. a tree branch) where they would try to eat them. However, the hard red seed coat is just a con, mimicking something fleshy and edible. The frustrated birds would then simply discard the seeds – dispersal achieved!

Nowadays, with their co-adapted dispersers long gone, the fruits of the Texas mountain laurel only reveal their seeds after the fruit wall has rotted away on the ground where the seeds might then be spotted by ground-dwelling birds like turkeys. Native Americans probably helped with the dispersal of the seeds, too, using them as beads and, although all parts of the plant are poisonous, as a hallucinogenic drug before they discovered the peyote.

Acknowledgements:

Thanks to Michael Eason (Alpine, Texas) for sharing his first-hand knowledge about the Texas mountain laurel and to Betty Alex (Terlingua, Texas) for contributing the image of a flowering specimen.

- Wolfgang -
 

Related Links

• The Millennium Seed Bank Partnership in the USA
• More about seed dispersal
• Seed Image Gallery
• Pleistocene epoch 

It’s early days yet, but not too soon to start planning this year’s Great Seed Swap event at Wakehurst. Our inaugural seed swap was held in September last year and was a great success. As well as hosting a talk by the inspiring James Wong on little-used vegetable varieties, and a Gardener’s Question Time session led by Matthew Biggs, we had demonstrations and tours given by our experts at Wakehurst.

James Wong and Matthew Biggs outside the Millennium Seed Bank at the Great Seed Swap, 2011

A successful first seed swap

The Millennium Seed Bank exhibition room was filled with gardeners, happily swapping seeds with the help of the campaign group Seedy Sunday. The national growing charity Garden Organic were also there, supplying interesting vegetable varieties through their Heritage Seed Library stall. Visitors were able to browse other stalls selling local produce, unusual seeds, and giving out information on local sustainability groups and campaigns. We also had a chef who prepared delicious meals from heritage vegetables that had been grown in the Wakehurst nursery.

The food diversity message

These seed swap events are designed to show people the incredible diversity of plant varieties that can be grown at home for food, and to encourage gardeners and horticulturalists to use as wide a range of plants as possible by exchanging seeds.

Rachael Davies, Processing Assistant at the Millennium Seed Bank, showing visitors how to process seeds on the seed swap stall

Early bookings for 2012

So, for this year’s seed swap we’ve started to get in touch with some of our friends from last year: those who supported our first seed swap and are keen to come back again.

• Thomas Etty esq., a supplier of heritage seeds and bulbs, will have a stall selling seed packets and gift boxes.
• Beans and Herbs will be selling seeds collected from different parts of the world, many of which are rare heirloom varieties with a fascinating history.
• Transition Horsham will attend, with information about their community group which is committed to building a network of flexibility and resilience in the face of the challenges of climate change and peak oil.
• The Rustic Mushroom Company will be selling woodland mushrooms and home-growing kits, and will even give demonstrations showing how to inoculate logs with mushroom spawn.
• Growers of rare plants, Edulis, will have unusual edible plants and vegetables, fruit trees and shrubs, as well as autumn perennials.
• And the Mid Sussex Wood Recycling Project will join us again, with their fantastic range of garden furniture made from recycled timber, by an environmentally responsible, not-for-profit social enterprise.

Packets of seeds from Garden Organic's Heritage Seed Library at the Great Seed Swap, 2011

This gives you a taster of what to expect on Saturday 20 October 2012. Watch this space to find out who will be coming to give talks on the day, and to discover other activities and stalls that will be included in the programme.

- Vanessa -
 

Related Links

• The Millennium Seed Bank Partnership
• Garden Organic and the Heritage Seed Library
• Seedy Sunday - Brighton and Hove based seed swap and campaign group

Seed of the Month - Ravenala madagascariensis

The most amazing blue seeds I have ever come across belong to the Malagasy traveller’s tree (Ravenala madagascariensis). 
 

Malagasy traveller’s tree (left) and a single seed (right)

If blue is such a rare colour among seeds, there must be a good reason why the Malagasy traveller’s tree seeds have evolved such an exotic colour. The reason behind it is a fascinating example of the tightly interwoven natural history of plants and animals.

The Malagasy traveller’s tree is a close relative of the bird-of-paradise (Strelitzia reginae) from South Africa and the very similar big palulu (Phenakospermum guianense) from South America.
 

Fruits of Malagasy traveller’s tree (left) and  big palulu (right)  (Images: Wolfgang Stuppy © RBG Kew)

Attracting animals

All three species belong to the Strelitziaceae family and all three produce seeds with edible appendages to attract animals for their dispersal. However, whilst the edible appendage of the seeds of Strelitzia and Phenakospermum has the appearance of a bright orange-red ‘wig’, the seeds of Ravenala are wrapped in an intensely blue, soft, wax-paper like appendage.

The red and black colour scheme is typical of, and very common in, bird-dispersed fruits and seeds whereas blue is extremely rare indeed.
 

 Bird-of-paradise flower (left) and its seeds (right) (Images: Wolfgang Stuppy © RBG Kew)

So why are they blue?

Clearly, there must be a reason why Ravenala, geographically isolated in Madagascar, has evolved seeds with an intensely blue rather than red appendage.

The answer lies in the very special fauna of the island. There are not many fruit and seed eating birds in Madagascar so some plants have entered co-adaptive relationships with other animals to achieve the dispersal of their seeds. One such alternative are the lemurs, a diverse group of primates endemic to Madagascar.

Seeds of  Ravenala madagascariensis (left) and a ring-tailed lemur from Madagascar (right)

And here comes the interesting fact...

Prosimians (‘half-apes’) such as lemurs and lorises (a related group of ‘half-apes’ found in Asia), have dichromatic vision and can only differentiate shades of blue and green but not red - whereas birds have very similar colour-vision to humans. So the shaggy red ‘wigs’ of the seeds of the bird-of-paradise flower would be wasted on the lemurs of Madagascar.

- Wolfgang -
 

Related Links 

• The Millennium Seed Bank partners in Madagascar
• Kew's Madagascar science team
• Orchids from Madagascar
• Expedition to Madagascar  
• Image gallery of seeds and fruit