Early one morning in 1985, a pair of researchers trekked into a spit of Colombian rainforest surrounded by coffee plantations. Their task was to identify all the epiphytes — plants that grow on other plants — in the forest canopy.
As Jan Wolf, a botanist now at the University of Amsterdam, measured tree trunk girth from the ground, volunteer field assistant Jan Klomp, an economist by training, clipped into a harness and climbed up a tall tree. From his high perch, Klomp called down to say he had discovered something more familiar in the Netherlands than in the rainforest: tulips. Perplexed, Wolf scoured the forest floor for fallen flowers.
“I found a large wooden fruit with some remnant red seeds that unmistakably belonged to the Magnoliaceae, whose flowers may resemble tulips for the non-botanist,” Wolf later wrote.
The seeds belonged to a previously unidentified species of magnolia tree, today fittingly named Magnolia wolfii. Wolf hoped that others would discover more of the same species. But in the 40 years since he and Klomp made their discovery, just six adult trees have been found, and M. wolfii is considered critically endangered. About half of the roughly 300 other known magnolia species are also under threat of extinction.
Scientists are now fighting to increase the plants’ odds of survival. Thousands of kilometers northwest of the Colombian rainforest, cryobiologist Raquel Folgado of the Huntington Botanical Gardens in San Marino, Calif., has spent years sorting out how to deep-freeze magnolias using a technique called cryopreservation. The hope is that, if magnolias ever go extinct, the cryopreserved plants can be thawed out and reestablished in the wild.
“It’s a garden on standby for things that can be lost,” Folgado says, “a frozen garden.”
Cryopreservation is an alternative to storing seeds in a facility known as a seed bank. Not all plants, magnolias included, are suitable for such preservation, either because they lack seeds or their seeds can’t withstand conventional storage. By some estimates, more than a third of critically endangered plants fall into that second category. But to date, only about 1 percent of plants ill-suited for seed banks have been cryopreserved. Challenges to scaling up include species needing tailor-made deep-freezing recipes and high initial costs.
The need is urgent, Folgado says. “Cryopreservation gives us the possibility of storing the plant … until you need it back. That can be [in] one year, two years, 50 years or a hundred years.”
But some experts caution that the time and resources spent on biobanking divert attention from preserving and restoring whole ecosystems. Just as a thawed-out Captain America must live in a radically different world from the one he left behind, a cryopreserved plant may not be suited to a future environment — it may survive only if its habitat does too.
“What is it that brought us to this situation where our only solution is to strip something of all of its context and stick it in a freezer and hope for the best?” asks Hannah Landecker, a sociologist and life sciences historian at UCLA. “There is no suspension of time.”
A short history of plant conservation
In his 1703 book, Nova Plantarum Americanarum Genera, Charles Plumier, a French monk and botanist for the royal court of King Louis XIV, renders in vivid detail the flowers, seeds and fruits of a plant on the Caribbean island of Martinique. Plumier named that plant “magnolia” after Pierre Magnol, a French botanist famous for systematically grouping plants into families.
Plumier’s account is among the first detailed European references to magnolias. As explorers brought those trees home with them, magnolias became a mainstay in European botanical gardens. The confines of these carefully manicured gardens demonstrated that plants could grow, and even thrive, far from home.
These gardens initially had little to do with conservation, says Xan Chacko, a feminist science studies scholar at Brown University in Providence, R.I., and an expert on the history of biodiversity conservation. Rather, the aim was to preserve the flavor of spices gleaned from distant locales or to cultivate wild plants, such as magnolias, for greater splendor.
Plant conservation became more important in the 20th century. The first seed bank, a repository of wild plant varieties related to food crops, appeared in the Soviet Union in the 1920s. Efforts to bank seeds intensified with the Green Revolution of the mid-20th century, when farmers increasingly switched to single, high-yield crops. With those monocultures imperiling wild crop varieties, scientists raced to collect the seeds of native plants.
Before the 1970s, most banks stored seeds at room temperature, sociologist Leon Wolff of the University of Marburg in Germany wrote last year in BioSocieties. But advances in refrigeration enabled banks to keep seeds just below freezing, thus extending their shelf life. Banks gave scientists the power to bring seeds out of cold storage for planting in fields; they could also hybridize plants in myriad ways to enhance genetic biodiversity and the plants’ ability to withstand changing climate conditions or disease outbreaks.
“The idea is you store possibilities for breeding,” Wolff says.
Those possibilities, for instance, inspired a committee of corn breeders, geneticists, botanists and administrators to travel across Latin America in the 1950s and collect thousands of maize seeds for storage in distant banks. Today, seed banks are a pillar of plant conservation, and food plants remain the focus. The poster child for the movement is the Svalbard Global Seed Vault in Norway, home to more than 1.3 million seeds from almost 6,300 botanical species.
But seed banks were never a panacea, Wolff says. Many plants lack seeds, including species that lost them during the domestication process. Estimates vary, but some suggest roughly 8 percent of plants worldwide have “recalcitrant” seeds that retain water. Many are concentrated in tropical areas. When the seeds are frozen, the water freezes and expands, rendering them sterile.
So alongside efforts to develop seed banks, scientists began experimenting with cryopreservation. Those efforts resulted in successfully freezing and thawing flax and carrot tissues in the late 1960s and early 1970s. But cryopreservation remained limited until the 1990s, when scientists worked out how to vitrify plant tissue, cooling it fast enough to prevent ice from forming — a process that puts the tissue in a glassy state.
Today, scientists have cryopreserved everything from apples and wasabi to ferns and willow trees. As with seed banks, cryobanks remain largely devoted to food. For example, a bank in Belgium houses 1,258 banana varieties, a bank in South Korea contains 1,158 garlic varieties and a bank in Peru stores 4,086 potato varieties.
At the Huntington, Folgado and her team have been studying how to deep-freeze avocados. The majority of commercial avocados derive from just one strain, which means a single pest could wipe out the world’s supply. If that happens, Folgado says, “we will not have guacamole.”
How to cryopreserve plants
In early March, the Huntington’s magnolia trees blaze fuchsia, yellow, white and orange. These vivid blossoms attract beetles for pollination.
Magnolias, among the earliest flowering plants, once spread across much of the world. But the Ice Age wiped out magnolias in extreme northern regions, and the plants’ range shrunk to include primarily eastern North America, Japan and China, areas where they have long been revered for their beauty and medicinal properties. Across the ages, people in China have used the bark of the Magnolia officinalis to treat everything from mood to stomach disorders. According to folklore, President Andrew Jackson planted Magnolia grandiflora seeds from his native Tennessee on White House grounds in memory of his late wife, Rachel.
Such beauty and a rich history may be reason enough to fight for magnolias. But saving plants that people don’t eat, or saving biodiversity for biodiversity’s sake, can be a tougher sell than saving food crops.
That mind-set irks many scientists. Plants are important for many reasons. In addition to food, for instance, a rainforest can provide medicines, raw materials and greenhouse gas mitigation as the plants inhale vast quantities of carbon dioxide. “My argument would be that there are all kinds of really important things that the rainforest does. Some of them serve humanity. Some are important for the maintenance of life on Earth,” Chacko says.
Botanical gardens, with their centuries-old collections of noncommercial but charismatic plants, are well positioned to lead efforts to maintain wild ecosystems, Folgado says. “If I didn’t have magnolias at the Huntington, I could not work in helping to cryopreserve them.”
Instead of traveling widely to locate specimens, all Folgado has to do is walk about 20 meters outside of her research building and snip a twig from a stubby magnolia. She can be back in her lab within five minutes — so quick that she doesn’t have to worry about the sample getting contaminated or oxidizing.
In a seed bank, keeping seeds at temps slightly below a kitchen freezer, about −18° Celsius, slows the molecular movement associated with aging. But the extreme cold of cryopreservation halts the aging process altogether. Cryopreserved tissue is, from a biological standpoint at least, suspended in time.
Yet deep-freezing life is incredibly finicky. Each species’s unique set of genes can react differently to the nutrients and hormones used for prepping the plant. And the scientific literature is littered with hundreds of unique deep-freezing protocols.
In her lab, Folgado demonstrates one such protocol, placing a magnolia snippet under a microscope. She painstakingly trims away the minuscule leaves furled around the shoot tip, which, like stem cells, can regenerate the whole plant. “This is kind of like a surgery,” Folgado says.
Next, she bathes the shoot tip in a cocktail of minerals, vitamins, hormones and antifreeze agents. That solution is hydrophilic, or water-loving, and thus draws water out of the shoot tip. In turn, the tip absorbs other substances in the solution that are less prone than water to crystallizing when frozen.
Now the plant sample is ready for the final step, vitrification. Folgado places the shoot tip in a droplet of solution on a strip of aluminum foil and rapidly cools it. She places the now-glassy tip inside a special vial and enshrouds it with liquid nitrogen so that it can live on at −196° C. Once inside a holding tank, the deep-frozen magnolia can, in theory, persist in a suspended state forever.
As a proof of concept, Folgado has removed cryopreserved shoot tips from storage, thawed them out and grown them into little plants. When they’re tall enough, she’ll replant them on the Huntington’s grounds.
Conservation in isolation
The Huntington is just eight kilometers south of Altadena, a neighborhood leveled by the wildfires that raged through parts of Los Angeles earlier this year. With climate change making such fires exponentially worse, single catastrophes can now wipe out entire ecosystems, making recovery nearly impossible.
Such risks point to the need for biobanks, proponents argue. Keeping seeds and tissues in cold storage can be an economical way to preserve botanical biodiversity.
Cryobanking has high upfront costs; deep-freezing a single plant variety ranges from $42 to $1,500 depending on tissue type and local labor costs, researchers estimated last year in the Annual Review of Plant Biology. Once frozen, though, maintenance costs drop to just $1 to $2 per year. Researchers estimate that the investment it takes to cryopreserve a single species should pay off within 10 to 15 years.
But cost is only one consideration. What happens when a plant has been isolated from the natural world for years, decades, centuries or more?
“What happens if you grow a magnolia tree in 250 years and there are [no] beetles?” Landecker asks. “You have a plant that will grow once and cannot reproduce.”
That concern isn’t totally hypothetical, says botanist Marcela Serna-González of Tecnológico de Antioquia in Medellín, Colombia. In 2006, one of Serna-González’s students helped transplant Magnolia silvioi trees to Medellín from elsewhere in Colombia. One of those trees wound up at the city’s botanical garden. The tree appears healthy. “It produces beautiful flowers, beautiful fruits,” Serna-González says, but “not a single seed.”
The large beetles that naturally pollinate the trees aren’t present. And though bees have taken up magnolia pollination in some other parts of the world, including at the Huntington, pollination is more specialized in the tropics. Bees in Medellín have not shown interest in the isolated magnolias.
“It’s easy to forget that [conservation] is not just about preservation of certain plants but their entire life worlds,” Wolff says.
Specimens in cryobanks are genetically frozen in time. Given the rapid pace of climate change, banked plants and their life worlds can start getting out of sync within years, research suggests. For instance, over the last 20 years, the mountainous Apennines region of Italy has grown drier and warmed by 0.6 degrees C. Scientists simulated those new climate conditions in a lab and compared the growth of alpine plants germinated from ancestral seeds collected in the early 2000s with that of seeds from the same type of plant collected in the last couple years.
Plants grown from the recent seeds were smaller than the ancestral plants — a size reduction that may enable the plants to conserve more water and reduce evapotranspiration, the team reported in 2023 in Biological Conservation. In other words, the plants that stayed on the mountain had adapted to a more arid life.
Both seed banks and cryobanks shift people’s focus from saving ecosystems in the present to preserving bits and pieces of those systems for an unknowable future, Chacko says.
Those concerns have prompted some scientists, farmers and activists to turn to alternative ways of preserving diversity, such as living seed banks. Unlike large seed banks, where access is often limited to scientists, living seed banks encourage, or even require, growers to regularly deposit and take out seeds. Farmers then grow crops under varying conditions and select for those that fare the best. That keeps the diversity alive.
For example, as part of Brazil’s conservation strategy, the government collaborates with small-scale farmers, who get seeds from a handful of related and under-utilized crops. The farmers experiment to see which varieties, or combinations of those varieties, grow best. Those seeds then go to other farmers and the plants to markets and restaurants.
Adherents of saving biodiversity in the field tend to dispute the idea that a plant can be isolated from its ecological and cultural context and stored in a museum for later use, Chacko says. The belief that plants can thrive without their surroundings, she adds, “is the science fictional element of the seed bank.”
Cryopreservation’s long odds
But sometimes science fiction can have some bearing in reality. Research hints at the possibility that scientists generations from now might be able to thaw out cryopreserved plants and reestablish them in the wild.
On occasion, scientists have discovered ancient plants or seeds frozen in nature and then grown them. In one case, squirrels buried the fruits of a small Arctic plant known as the narrow-leafed campion (Silene stenophylla) in burrows in Siberia some 32,000 years ago. Russian scientists found some of those fruits, which had been encased in permafrost. They extracted tissue and successfully coaxed the ancient plant into flowering, the researchers reported in 2012.
The feat demonstrated that long-frozen plants can be thawed and regenerated.
In another instance, reported last year, a team of Italian scientists collected some 20,000 seeds from 26 species stored in herbarium collections in Italy and Belgium. Some of those seeds, such as those from the Silene flos-cuculi, a wildflower with ragged white or purplish petals, were over a century old. The team helped those seeds germinate using a variety of techniques known to help plants grow. Roughly 1 percent of seeds, drawn from 10 species, germinated, the team reported in Taxon.
Many of these plants are related to now-extinct species, so it’s another hint that seed banking or cryopreservation might work to bring back long-lost plants, says Giulia Rocchetti, a botanist at Roma Tre University in Italy. The fact that seeds stored in such poor conditions still grew is amazing, she adds. Imagine what that means for resurrecting plants stored in optimal conditions.
Despite the long odds of successfully transplanting and maintaining a thawed-out plant in some future ecosystem, cryopreservation and seed banking research is worthwhile, Folgado argues. Even if the whole plant never winds up back in the wild, the genes that have been saved may one day prove crucial for medicines. Or, she adds, perhaps the hormones used to cryopreserve plants could point to ways for scientists to encourage plants to grow outside their normal ecological range — think warm-weather-loving avocado trees thriving in drizzly, cold Seattle — no genetic modification required.
“I always question myself whether this can have a real value or not,” Folgado says. “What I know is that there will be some things that will have a big value. If we don’t preserve them, we will not know.”
Reflecting on the Italian experiment, she says: “Even if you have 1 percent germination, that’s more than 0.”
