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LONDON — For nearly two decades, conservation scientists have used a powerful metric to identify the world’s most irreplaceable animals on the brink of extinction: the aye-aye, the pangolin, the axolotl. But one vast kingdom of life remained invisible in those calculations. That changed this spring when a landmark study in the journal Science delivered the most comprehensive assessment ever of the botanical world’s fragility, revealing that more than 21% of the evolutionary history carried by Earth’s flowering plants — the angiosperms that sustain nearly every terrestrial ecosystem — now faces extinction.
The finding, the result of an international collaboration spanning the Zoological Society of London, the Royal Botanic Gardens, Kew, and Boise State University, marks the first time the EDGE metric — Evolutionarily Distinct and Globally Endangered — has been applied to all known flowering plant species.
A Metric Built for Animals, Turned on the Garden
Introduced by the Zoological Society of London in 2007, EDGE combines a species’ extinction risk with its genetic uniqueness within the broader tree of life. For years, it spotlighted unheralded animals — creatures rarely featured in nature documentaries yet representing entire, irreplaceable branches of evolution.
Rikki Gumbs of the Zoological Society of London, who co-led the new analysis, noted that the approach has let conservationists flag overlooked animals for urgent protection for nearly two decades. “Plants remained comparatively invisible,” he said, describing them as often dismissed as mere backdrop for photographs of bees and tigers.
That imbalance was never about low stakes. It was a data problem. Assessing extinction risk for an animal is one thing; doing so for the roughly 335,000 species of flowering plants that carpet the planet’s ecosystems is another matter entirely.
Building a Family Tree for a Third of a Million Species
Led by Félix Forest, a plant evolutionary biologist at Kew, alongside teams from London, Boise State, and international partners, the project constructed a tree of life and generated extinction-risk estimates for every known flowering plant species. Researchers assigned EDGE scores to all 335,497 species using molecular data cross-referenced against the IUCN Red List of Threatened Species. It stands as the single largest species-prioritization assessment ever undertaken in conservation science.
Forest put the scale in context: angiosperms outnumber the largest previously EDGE-assessed animal group — ray-finned fish — by more than tenfold. “Compiling comparable data for flowering plants was no small task,” he said, adding that the scores now provide vital information to spotlight irreplaceable, threatened species that conservation efforts have often overlooked.
The Number That Should Worry Us: 21.2%
The headline figure is stark: the team estimates 21.2% of angiosperm evolutionary history is at risk of extinction, and has identified 9,945 priority species that disproportionately account for that threatened diversity. To put that in perspective, the figure is nearly double the equivalent risk measured across jawed vertebrates, a group encompassing everything from sharks to elephants, where the comparable rate sits at around 13%.
Those 9,945 species — dubbed EDGE species — represent roughly 3% of all known flowering plants, but their evolutionary weight is disproportionate to their numbers. Losing them would mean pruning branches of the plant tree of life that took tens of millions of years to grow and cannot be recovered.
Perhaps the most sobering context comes from how little formal attention these species have received. Sven Buerki, a botanist at Boise State University and a contributor to the study, framed the disparity bluntly: more than two in five plant species are estimated to be threatened with extinction, yet fewer than one in five has ever received a formal threat assessment — compared with over 80% of vertebrate groups. “Plants,” he said, “have been dying in the dark.”
Faces of the Crisis
Among the newly flagged priority species are some remarkably familiar names. The vanilla orchid — source of the world’s most popular dessert flavoring — now sits among plants whose evolutionary uniqueness and endangerment mark them for urgent attention, alongside relatives of the corpse flower, whose rare, cavernous blooms draw crowds to botanical gardens whenever they open.
Then there is a stranger case: the jellyfish tree, or Medusagyne oppositifolia, found nowhere on Earth except a handful of rocky outcrops on the island of Mahé in the Seychelles. Believed extinct until a few surviving individuals were rediscovered in the 1970s, it is the sole member of its genus, its jellyfish-shaped seed pods giving the species its common name. Fewer than 100 mature jellyfish trees are thought to survive in the wild, confined to four small populations near Seychelles’ coast. With no close living relatives, its loss would not just erase a species — it would prune an entire limb from the angiosperm family tree.
Other headline cases include ancient, solitary lineages such as Amborella trichopoda, a modest New Caledonian shrub whose evolutionary lineage split from all other flowering plants some 130 million years ago — making it, by the study’s measure, the single most evolutionarily distinct angiosperm alive today.
A Roadmap, Not Just an Obituary
For all its grim arithmetic, the study’s authors frame it as a tool for triage. The researchers calculate that protecting just 5.9% of species, selected by EDGE ranking, would safeguard half of all threatened angiosperm evolutionary history — and protecting the full EDGE list would preserve 16.6% of it. With finite conservation budgets and infinite need, EDGE scores offer a way to direct resources toward species whose loss would cost evolutionary history the most.
Some translation from data to action is already underway. Buerki said his team’s goal is to fold the results directly into Flora of the World, an online platform, so that anyone searching for a species can see not just where it grows, but how evolutionarily irreplaceable and endangered it is. At Kew itself, the EDGE metric has already begun shaping decisions inside its Living Collections, guiding which specimens horticulturists prioritize for cultivation and seed-banking.
Why It Matters Beyond the Greenhouse
The paper’s authors situate their findings within a broader argument circulating in conservation biology for years: global biodiversity policy has consistently treated evolutionary diversity as worth protecting, yet plants were left out of the assessments meant to operationalize that principle. That taxonomic imbalance, they argue, has undermined plant conservation for decades, even though preserving evolutionary lineages underpins both the immediate benefits people draw from ecosystems and the future of life on Earth.
It is a reminder that the animals typically pictured on conservation reports — the pandas, the polar bears, the tigers — depend on the quieter, rootier world sustaining them. Gumbs’s framing captures the stakes succinctly: “Flowers and forests were never simply scenery.” This study suggests they are running out of time on their own terms — and now, for the first time, science has the numbers to prove it.