LONDON — For nearly twenty years, conservation biologists have used a powerful tool to identify animals teetering on the edge of extinction, from the bizarre aye-aye to the scaly pangolin. But one vast kingdom of life was left out of the assessment entirely: flowering plants. That blind spot ended this spring when a landmark study published in the journal Science delivered the most comprehensive diagnosis yet of the botanical world’s fragility, revealing that more than a fifth of the evolutionary history carried by Earth’s flowering plants now stands to be lost forever.
A Metric Built for Animals, Turned on the Garden
The tool behind the finding is called EDGE — Evolutionarily Distinct and Globally Endangered — a metric developed by the Zoological Society of London in 2007. It combines a species’ extinction risk with how genetically unique it is within the broader tree of life. For nearly two decades, EDGE scores highlighted the plight of overlooked animals that represent entire, irreplaceable branches of evolution but rarely headline nature documentaries.
Rikki Gumbs of the Zoological Society of London, who co-led the new analysis, said the approach has let conservationists flag neglected animals in urgent need of protection for years, while plants remained comparatively invisible — dismissed, in his words, as mere backdrop for photographs of bees and tigers.
That imbalance was never for lack of 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 — angiosperms — that carpet the planet is another matter entirely.
Building a Family Tree for a Third of a Million Species
Led by Félix Forest, a plant evolutionary biologist at the Royal Botanic Gardens, Kew, alongside teams from the Zoological Society of London, Boise State University, and international collaborators, the project set out to construct a tree of life and generate extinction-risk estimates for every known species of flowering plant on Earth.
Researchers assigned EDGE scores to all 335,497 flowering plant 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 of the undertaking in context: angiosperms outnumber the largest previously EDGE-assessed animal group — ray-finned fish — by more than tenfold. The scores, he said, now provide vital information needed to spotlight irreplaceable, threatened species that conservation efforts have often overlooked, in service of the benefits that all life on Earth depends on.
The Number That Should Worry Us: 21.2 Percent
The headline figure is stark. The team estimates that 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. That 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%.
The 9,945 species carrying that risk — dubbed EDGE species — represent roughly 3% of all known flowering plants, but their evolutionary weight is disproportionate to their numbers. Losing them would mean losing 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, in other words, 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 the plants whose evolutionary uniqueness and endangerment mark it for urgent attention, alongside the corpse flower’s malodorous relatives, whose rare 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. Today, fewer than 100 mature jellyfish trees are thought to survive in the wild, confined to four small populations. 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 rather than a eulogy. The researchers calculate that protecting just 5.9% of species, selected by EDGE ranking, would safeguard half of all threatened angiosperm evolutionary history — and that 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 the species whose loss would cost evolutionary history the most.
Some of that 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 how endangered — it is. At Kew itself, the EDGE metric has already begun shaping decisions inside the institution’s own 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 that has circulated in conservation biology for years but rarely with plants at its center: global biodiversity policy has consistently treated evolutionary diversity as something worth protecting, yet plants — for decades — were left out of the assessments meant to operationalize that principle. That taxonomic imbalance, the authors argue, has undermined plant conservation for decades, even though the preservation of 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. They are, this study suggests, running out of time on their own terms — and now, for the first time, science has the numbers to prove it.
