When it comes to plants, the most biodiverse spot on the planet isn’t where you think it is. It is not in the Amazon, nor the flooded expanse of the Pantanal. It can’t be found in the deep forests of Madagascar or even on the many islands of Indonesia. Instead, you can find it in the quintessentially English countryside of West Sussex, a bit over an hour’s drive south of London in light traffic, just off the B2028. If you reach The Gardener’s Arms pub, you’ve gone a bit too far. But if your satnav does its job properly, you will find among the hedgerows and gently rolling hills a small side street that takes you into the Kew Botanic Gardens at Wakehurst. It is there, in the midst of over 130 sprawling hectares of tended meadows, woods and gardens, that you’ll see an enormous Elizabethan mansion. It’s a handsome building, but a short distance behind it is something far more interesting. At first glance it appears to be a collection of domed greenhouses, albeit high-end ones with a modern architectural flair. This is the Millennium Seed Bank, and there is far more than meets the eye there. Really, the best part is entirely underground: a secure storage facility which currently holds over 2.4 billion seeds from nearly 40,000 wild plant species from around the world. The series of six vaults, which are cooled to −20°C, are bomb-proof, radiation-proof and flood-proof. According to Kew, the space is large enough to fit ‘30 London double-decker busses’ – a uniquely British unit of volume if ever there was one – the point being that this location technically contains more plant biodiversity per square metre than anywhere else in the world. And there is room for more.
Wakehurst’s official history dates back to the 1200s, but archaeological evidence suggests it has been inhabited since the Iron Age and probably longer. Arrowheads and pottery shards regularly turn up there, as do bones. The whole region seems to have attracted both modern and archaic humans for many millennia. They came and they went, and then others came and went, so it seems to have been a bountiful place. Since its formal establishment in the Middle Ages, Wakehurst changed ownership numerous times as the fortunes of West Sussex gentry rose and fell, until it was purchased at the turn of the 20th century by a gentleman named Gerald Loder. Loder was an irrepressible plant enthusiast who had come of age during the Victorian heyday of horticultural mania and grand greenhouses. He spent decades collecting plants and seeds, either directly or by sponsoring global expeditions, and together with his head gardener, Alfred Coates, he turned Wakehurst into something of a botanical spectacle. The West Sussex soil likely had a lot to do with their success, as it’s highly variable, ranging from heavy clay in some places to sandy in others, making it well suited to growing very different plants from all around the world. The gardens were continued by the subsequent owner and in time the estate was bequeathed to the National Trust and placed under the management of Kew Gardens.
All this is precisely how you end up with an industrial-sized freezer being wheeled into an old chapel, which is what happened in 1976 when the new caretakers decided that they needed a better way of storing their seeds. This resulted in a very big freezer, resembling a giant sugar cube, being placed in the Wakehurst chapel, and subsequently the seeds of many of Britain’s endemic plant species were kept, for a time, under the serene gaze of a few stone angels and several stained-glass saints. Of course, given the ever-growing size of Kew’s seed collection, it was clear something more purpose-built would be required, and eventually plans were drafted for an everything-proof, thirty-double-decker-busses–sized facility. In the year 2000, the Millennium Seed Bank (MSB) was officially opened.
The entire seed collection has expanded over the past two decades through research programs and seed-collecting expeditions carried out in collaboration with international botanic gardens and research centres. Today, the MSB houses seed accessions representing almost all seed-bearing plants in the United Kingdom, as well as seeds from about 190 other countries and territories. These include a large number of representatives from the world’s thirty-six biodiversity hotspots, places identified by conservationists as priority areas for protection because they contain an enormous number of unique species that are under threat of habitat loss.
Unlike the Svalbard Global Seed Vault and the CGIAR gene-banks, the MSB does not focus on crop species but instead endeavours to preserve the seeds of wild plant species as part of an ambitious effort to conserve Earth’s wild biodiversity. There are seeds collected from the slopes of active volcanoes in Indonesia and from fields in Finland. There are seeds from meadows in Slovenia, desert gullies in Jordan, flooded plateaus in Nigeria, and Colombian rainforests, as well as samples collected from American prairies and Australian bushlands. The list goes on and on. Seeds from around 16 per cent of the world’s seed-bearing plant species are banked at the MSB. Yet, the vaults could be filled with seeds from 75 per cent of the world’s wild seed plant species, which is precisely what the MSB intends to do. There are also seeds from plants that no longer exist in the wild at all, including those of the yellow fatu flower Abutilon pitcairnense, which had been collected on Pitcairn Island prior to the mudslide that erased the species from the wild in 2005.
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When Eberhard Fischer encountered that tiny waterlily in Rwanda, he suspected the species was not long for this world. He brought some living specimens to two botanical gardens in Germany – one in Mainz and another in Bonn – but as the story goes, attempts to revive the population did not go well. The collected plants were mercifully long-lived and some were still alive more than twenty years after their original collection. Furthermore, they were self-pollinating and produced many seeds. But that’s where the luck ended. The seeds, if they germinated at all, produced seedlings that did not thrive. None reached adulthood, so were unable to produce more seeds. There it was, a species that was now extinct in the wild, and it could not be propagated. The last remaining specimens had only so much time left.
Enter a botanist by the name of Carlos Magdalena. Magdalena, who works at Kew, has something of a reputation in the botanical world. Some call him the Plant Whisperer, others call him the Code Breaker, and famed primatologist Dame Jane Goodall once called him ‘an inspiration’. Some, including Sir David Attenborough, have called him the Plant Messiah. Certainly, Magdalena seems to have a talent for resurrection, having coaxed a number of plant species back from the edge of extinction. As it happens, Magdalena absolutely loves waterlilies. He had heard about Nymphaea thermarum and its fussy behaviour and was keen to have a go. The botanists at Bonn Botanic Gardens were happy for the help, and in July 2009 Magdalena found himself in possession of around 200 seeds.
‘When I received this donation from Bonn, I realised how important it was for the survival of the species to find a way of growing them successfully,’ remarked Magdalena when the research was announced back in 2010. ‘At first they didn’t seem to respond to any of the traditional ways of treating these plants and they remained weak and failed to develop and eventually died.’ Things were looking bleak indeed. Rumour has it that, at one point, Magdalena was down to the last twenty seeds. No pressure. But then, as Magdalena recounts in his aptly titled book The Plant Messiah, he had a revelation. Going back through the plant’s history, including Fischer’s original notes, he realised that while most waterlilies germinate and grow in deeper water, these tiny lilies had been found at the edge of hot springs, in the very shallow run-off – practically mud – which was 10–15°C cooler than the centre of the springs. Well, that changed everything. In prior experiments, seed germination had been attempted with seeds submerged in water that Magdalena now realised was far too hot. It was also far too deep. All plants need CO2, of course, and while it is readily available in air, CO2 availability in water is much lower because it diffuses far more slowly. To compensate, aquatic plants are often efficient at capturing CO2 underwater, but Magdalena wondered if maybe this little waterlily wasn’t so good at it. He took some of those final N. thermarum seeds and planted them in very shallow water, such that they would not dry out yet could access CO2 in the air. Meanwhile, unbeknownst to Magdalena at the time, there was now only one N. thermarum waterlily still alive back in Bonn – that is, until the night a rat scurried into the greenhouse and ate it.
Fortunately, Magdalena’s idea worked. The seeds germinated. The seedlings grew, thrived and reached adulthood. Most wonderfully, they produced more seeds. Little by little, then, Magdalena was able to grow the population. Eventually, around two dozen of the new waterlilies were placed on display in the Princess of Wales Conservatory at Kew Gardens, although in hindsight that would prove to be less than a great idea. On a January afternoon in 2014, the conservatory manager entered the grand structure to be met by a very upset apprentice who had just counted the waterlilies and found that one was missing. Someone had carried out a plant heist in broad daylight, stealing one of the world’s rarest waterlilies. The police were called in, but the perpetrator/s were never found. The waterlilies are much more closely guarded these days. The seeds are stored in the Millennium Seed Bank. The species is still considered extinct in the wild, but there are plans to soon repatriate this tiniest of waterlilies to Rwanda.
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There are limitations to what the Millennium Seed Bank and others can conserve, and this has to do with the nature of seeds themselves. In order to preserve seeds, the MSB and many other seedbanks first dry the seeds and then freeze them. That drying process is called desiccation, and it’s done for precisely the same reason you should wear gloves and warm boots outside when winter temperatures drop below 0°C. If you freeze a seed with high or even moderate water content, small ice crystals will form inside it and rupture the membranes of nearby cells, which can damage or even kill the delicate embryonic plant tissue. Something similar happens during frostbite: if the temperature of your extremities, say your toes or fingertips, falls even a little below 0°C, ice crystals will form in your blood vessels and cause cellular damage. So MSB technicians dry seeds down prior to freezing, so that ice crystals won’t form.
As explained in an earlier chapter, seeds that tolerate this drying and freezing process are called orthodox seeds. Dessication leads to a dramatic slowdown of metabolic activity in these seeds and, as a result, the little plant embryo enters a sort of suspended animation. The majority of seed plant species in the world produce orthodox seeds. However, at least 8 per cent of the world’s seed plants produce seeds that do not tolerate this drying process – the so-called recalcitrant seeds. For reasons that are still not entirely clear, the plant embryos in these seeds must remain hydrated in order to stay alive. Try to desiccate a recalcitrant seed and it will quite literally shrivel up and die.
Now, 8 per cent of the world’s seed plants might not seem like much, but this poses a big challenge for biodiversity conservation in tropical and subtropical regions because that’s precisely where most recalcitrant-seeded plant species live, and where they account for almost 19 per cent of local plant species. Mango seeds, avocado seeds, citrus seeds, cacao beans – alas, chocolate – as well as the seeds of coffee and tea plant species, are all recalcitrant. Recalcitrance is not entirely limited to the tropics and subtropics, though, as some temperate species are represented, too. Oaks produce recalcitrant seeds, as do chestnuts. Around 33 per cent of all trees produce such seeds. By extension, this means that the seeds of a huge number of the world’s tree species are not considered ‘bankable’. Moreover, recalcitrant-seeded species are disproportionately represented among threatened plant species: they comprise 35 per cent of plants listed as vulnerable on IUCN’s ‘Red List’, 27 per cent of endangered species and, most alarmingly, 36 per cent of critically endangered plant species.
Cathy Offord, whom we met in Chapter 4, thinks a lot about the challenges presented by non-orthodox seeds. As well as working at Sydney’s Royal Botanic Garden, she is a principal research scientist and manager of the Australian PlantBank, which is located at the Australian Botanic Gardens at Mount Annan, about an hour’s drive south-west of Sydney. Set on more than 400 hectares in the Australian countryside, these gardens are a far cry from the pastoral greenery of southern England: warmer, drier, more sun-bleached. There are 4000 species growing at Mount Annan, including hundreds of species each of eucalypts, acacias and grevilleas. There are hakeas, lilly pillies and golden wattles as well as cycads, bottlebrush, and hardy waratah shrubs with their enormous crimson blooms. There is also a Wollemi pine. Often called a ‘living fossil’, this species was believed to have gone extinct sixty million years ago, only to be discovered alive and well growing at the base of a deep gully in Wollemi National Park in the Blue Mountains. There are fewer than 100 of the pines there, and only a few people in the world have been trusted with the location, including the firefighters who risked their lives to save the ancient grove from the Gospers Mountain mega-fire.
It seems there are many things at Mount Annan that are sitting quietly on the brink of extinction. Here, you will also find the last remnants of a native woodland ecosystem that once sprawled over more than 125,000 hectares east of the Blue Mountains. That was before Europeans arrived in Australia in the 18th century and cleared most of it for farms and grazing land. Only 35 hectares of this habitat, called the Cumberland Plain Woodland, now remain. For comparison, that’s scarcely more than one-tenth the size of New York’s Central Park.
The Australian PlantBank sits just near the edge of that remaining woodland. It’s a long structure of mirrors, steel and concrete. The facility’s role is to preserve Australian native plant species, with a particular focus on those native to the state of New South Wales. They have stored accessions representing more than 5000 species, some 100 million seeds in all. But there is more to do. There are a lot of unique species in Australia, and quite literally a lot of ground to cover. Collaborations are vital. The PlantBank is a member organisation in the Australian Seed Bank Partnership, which is precisely what it sounds like: a wider network of seedbanks around the country.
The PlantBank has a seed vault because many Australian species, including a large number belonging to the eucalyptus family, produce orthodox seeds. As does the Wollemi pine, which is lucky. Such seeds are collected, dried, frozen and stored away to preserve their genetic diversity. Unlike Svalbard or Millennium, the PlantBank’s seed storage facility is not an underground structure, but it is nonetheless robust and necessarily bushfire-resistant. Offord tells me that there are also a number of recalcitrant-seeded species to contend with. Australia is a big place, after all, with enormous dry regions as well as huge swathes of tropical and subtropical areas. Offord gives the example of lilly pillies, which are native to Australian rainforests. Intriguingly, although lilly pillies and eucalypts both belong to the same family, Myrtaceae, their seeds are quite different. Lilly pilly seeds are recalcitrant, being ill-suited to long periods of storage – not in a seedbank, not even in the soil. In fact, they have such short life spans that they don’t even go through a dormancy cycle, says Offord. ‘They germinate when they hit the forest floor,’ she explains, noting that sometimes they’ll even germinate when they’re still on the tree. They are big fleshy seeds, she says, pointing out that this is part of the problem. Recalcitrance often comes down to the ratio of the seed coat thickness to the size of the seed – big seeds with thin seed coats are often recalcitrant, as they just dry out too quickly.
Offord tells me about the endangered magenta lilly pilly, Syzygium paniculatum. ‘It has a typical lilly pilly fruit, which is quite large,’ she says, ‘and it’s very fleshy.’ The PlantBank scientists are working to save the species but it isn’t easy. First, along with other members of the Myrtaceae family, they’re susceptible to myrtle rust, an invasive fungus that was first detected in Australia in 2010 and which now infects more than 350 Australian native plant species up and down the eastern seaboard and beyond. Among its many pernicious effects, myrtle rust damages leaves and disrupts the reproductive process of the plants it targets. But even for healthy lilly pillies, standard seedbanking just won’t work. ‘When they’re dried they lose viability,’ says Offord. ‘They’re effectively killed by drying, so that does cause problems for us.’
It causes problems in Hawaii, too.
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In addition to their reputation for luaus and good surfing, the Hawaiian islands are world-famous for their natural beauty and incredible biodiversity. But there is trouble in paradise. ‘It’s called the extinction capital of the world,’ says Dustin Wolkis, manager of the seedbank and laboratory at the National Tropical Botanical Garden in Hawaii, explaining that 90 per cent of Hawaii’s endemic species occur nowhere else on Earth, and that many of these plants are threatened or endangered, now requiring a lot of care to ensure they don’t slip out of existence. ‘Hawaii has 0.01 per cent of the landmass of the United States,’ says Wolkis, ‘but we have over half of all endangered plant species.’
Moreover, Hawaii has eight main islands as well as scores of smaller ones, and it’s not uncommon for certain of these endemic species to occur only on one island, says Wolkis. He also tells me that the National Tropical Botanical Garden (NTBG) recently assessed all of the single-island plant species on the island of Kaua‘i, where the institution is based. ‘These are Kaua‘i endemic species, so they occur on Kaua‘i and no other island,’ he explains. And the tally? ‘There are 255 of them, and 100 per cent of them were in a threatened or extinct category, and 10 per cent of them were already extinct or extinct in the wild. So that gives you an idea of the level of endangerment.’
Deforestation and forest degradation caused a lot of historical habitat loss, most of which took place in the 19th century when Europeans arrived and began cattle ranching. Today, the primary threat to Hawaiian biodiversity is invasive species, says Wolkis. ‘About half of our total flora is introduced. We have about 1500 native species and about 1500 naturalised species.’ Those introduced species are competing with endemic species for space and resources like nutrients, water and sunlight. Then you have the animals. ‘Hawaii only has two native mammals: one of them is a monk seal and one of them is a bat,’ says Wolkis, explaining that when the Polynesians arrived, they introduced pigs to the islands. Europeans later brought goats, rats, deer and more pigs, which now wreak havoc on the ecosystem. Wolkis says: ‘Rats, they eat not just the seeds in the fruit, but they’ll also nibble on stems and girdle these plants with small stems. They’ll eat seedlings, and the goats and the pigs will just trample everything. It’s really bad. So, some of these plants that are super-rare, the only place they still occur are on vertical cliff faces where even the goats can’t get to them.’
Then there are about half-a-dozen species of biting mosquitoes, Wolkis tells me. They’re all introduced, there being no native species of mosquito in Hawaii, and they carry diseases. ‘They carry avian malaria and avian pox, so all of our first birds are quietly going extinct in the forest right now as we speak. They have interactions with the plants both in dispersing and also pollinating, and so we’re losing those.’
The NTBG Seed Bank is building its collection of seeds to represent as many endemic Hawaiian plants as possible. For conserving the ‘ultra-rare’ species, NTBG partners with the Plant Extinction Prevention Program (PEPP), which focuses on the nearly 240 Hawaiian plant species that have fewer than fifty individuals remaining in the wild. PEPP botanists like Steve Perlman will go to extraordinary lengths to collect the seeds of these critically endangered plants. He abseils down the sheer sides of volcanic cliffs to reach places even goats dare not venture, or descends by helicopter winch into remote canyons. Sometimes it’s necessary to paddle an ocean kayak to reach a rare plant on some otherwise inaccessible patch of coastline. The seeds Perlman brings back are analysed at the NTBG Seed Bank laboratory and carefully stored.
Of course, this is only one part of the conservation effort. ‘Hawaii’s been kind of in crisis mode,’ Wolkis tells me. ‘Get the seeds, save the species. That’s what we used to think. Now we’ve kind of gone beyond that, thankfully, and we realise that, well, seedbanking is more like a genetic safety net. What we’re actually doing is we’re trying to save alleles.’
It’s all those alleles, or gene variants, that give us so much biodiversity. The alleles are found within the genomes that are furled within the plant embryos tucked inside the seeds. But it’s not enough to just stow them away in a freezer, a cold room or a jar. ‘The whole point of the seedbank is it supports in situ conservation,’ Wolkis tells me. The bank works with NTBG field teams and PEPP, using those stored seeds to rebuild diverse plant populations. There are so many species to save and so many habitats that need rebuilding, yet resources are limited, so it often becomes a matter of triage – to prioritise and save what you can. And right now, one of the most pressing rescue operations relates to Hawaii’s native ‘ōhi‘a lehua.
‘Ōhi‘a lehua (Metrosideros polymorpha) is an evergreen flowering tree species that, along with eucalypts and lilly pilly, belongs to the Myrtaceae family. It is endemic to Hawaii, with several varieties found across multiple islands. Wolkis tells me, ‘They are our foundational forest trees in the mesic and the wet forests. [‘Ōhi‘a] provides shelter and nectar for birds, shelter and habitat for snails, insects and other invertebrates. It filters the water that ultimately we end up drinking.’ Moreover, when an ‘ōhi‘a lehua dies, it becomes a nurse log providing nourishment for seedlings and other living organisms. ‘It’s arguably the most ecologically important plant on our islands,’ says Wolkis, going on to clarify that ‘ōhi‘a lehua is not a keystone species, whose ‘biomass is disproportionate to the ecosystem services that they provide. Because [‘ōhi‘a lehua] is the most abundant tree in the forest, by definition, it can’t be a keystone species, but it is foundational.’
A common feature in both keystone species and foundational species, according to Wolkis, is this: ‘If you remove that species from the ecosystem, the ecosystem collapses.’ Until relatively recently, that wasn’t a big concern for the ‘ōhi‘a lehua. After all, this isn’t some rare species found only at the base of one waterfall in one valley on one island. While it is unique to Hawaii, it is incredibly common there. They’re even found in the yards of many Hawaiian homes. And that’s where the trouble was first noticed. Sometime around 2012, Hawaiians started reporting that something was wrong with their ‘ōhi‘a lehua. All the leaves would turn brown and then fall off – always a worry for an evergreen – and then, in a matter of weeks, the tree would be dead. Soon it was happening on all the islands. It became known as Rapid ‘Ōhi‘a Death (ROD). In time, botanical forensics revealed that ROD is caused by two newly described species of ceratocystis fungus. Hawaiians are now doing their level best to stop the disease from spreading, but it’s becoming increasingly clear that the once-abundant species is in bad shape, with myriad downstream effects predicted for the entire Hawaiian ecosystem. And so Wolkis and his colleagues are working quickly to preserve as much ‘ōhi‘a lehua genetic diversity as possible. In fact, they have collected and stored several million ‘ōhi‘a lehua seeds so far. The good news is that ‘ōhi‘a lehua seeds are very small – Wolkis says he can fit 10,000 of them in the palm of his hand – and they’re orthodox. That means while intensive conservation efforts are made to eradicate the disease, the genetic diversity of the species can be preserved.
It could have been a lot worse. Hawaii is tropical, after all, and there tends to be a higher incidence of recalcitrant-seeded species in tropical ecosystems. Although it turns out Hawaii doesn’t have as many of these as was once thought, there are still plenty of rare Hawaiian species that produce recalcitrant seeds, as well as seeds that fall into a troublesome middle ground between orthodox and recalcitrant. Wolkis points out that while orthodox and recalcitrant sound like neat and tidy categories, the reality is that seed storage behaviour is not a dichotomy, it’s a gradient. Some seeds might really be orthodox – they will tolerate both drying and freezing, and they can be stored for years, maybe centuries or longer. Other seeds might be incredibly recalcitrant and this makes long-term storage difficult. If you want to preserve their genetic material, you need to use far more technical approaches like tissue culture, in which plant tissue is extracted and kept alive in a nutrient medium, or snap-freezing at −180°C. Another option is to simply grow the plants and keep propagating them as long as humanly possible. Then there’s this middle ground between orthodox and recalcitrant, says Wolkis. Some species, like many alpine seeds, don’t last long in storage no matter how you dry or freeze them. There are also seeds that kind of tolerate drying – better than recalcitrant but worse than orthodox.
Furthermore, there’s another behaviour that’s really a bit weird, and it seems to affect a lot of Hawaiian species. Wolkis asks me if I’ve heard of a Hawaiian plant called Brighamia insignis. I haven’t. It’s sort of like a plant version of a panda, he says, meaning that it’s threatened and it’s very difficult to get it to produce offspring. ‘We have a lot of pandas in Hawaii, but it’s like the main panda,’ he says.
B. insignis, or ‘Ōlulu, is often called the cabbage-on-a-stick plant. This succulent can grow over 4 metres and looks very much like its colloquial name suggests. As a lobeliad it belongs to the Campanulaceae family, which is the biggest plant family in Hawaii and entirely endemic. This family has the most endangered species and the most extinctions, says Wolkis. Now the fate of wild ‘Ōlulu hangs in the balance: critically endangered, on the verge of extinction in the wild. A few individuals are rumoured to remain on the island of Kaua‘i, though there might be just one, and some say even that is already gone. Seed collection and storage have been pivotal in enabling cultivation and preventing the species from vanishing entirely. But ‘Ōlulu seeds, like many of the seeds produced by Campanulaceae plants, are ‘intermediate freeze sensitive’ – they tolerate being dried but die when you try to freeze them. The seeds are kept refrigerated, says Wolkis, but it’s not great because they usually die within twenty years.
This is why scientists like Wolkis, Offord and others are trying to better understand precisely what’s going on inside these seeds, and it highlights how most plant genebanks are far more than storage facilities.
Every seed contains an evolutionary past and a possible future, and once the last seeds of a species die, that vanishes forever. To save seeds is to buy time. But there’s still a lot that remains unknown about how long seeds last or why each has the puzzling life span that they do. Why do some grow old and die in what seems to be a flicker of time, while others appear to evade the ravages of time altogether? How does a Judean date palm seed rest quietly near the edge of the Dead Sea for over 2000 years and still germinate, while the sunflower seeds in a slightly out-of-date packet are as good as dust?
Most life on Earth relies implicitly on how well seeds endure from one season to the next, or from one century to another. We hope each time that they will come good after winter, after a long drought, or after a mega-fire. But it doesn’t always happen, and even when it does, it’s still not entirely clear how. Consequently scientists continue to tease out the hidden lives of seeds to find out exactly how they disperse through time. The answer is important because a great deal of future food security and biodiversity conservation depends on the life spans of seeds and our ability to extend them. With all those living seeds come all those genomes, all those alleles, all those solutions to problems, all that food on the table, all those species that can be coaxed back into existence and given a chance to thrive. All those possible futures.