LONDON — For two decades, conservation scientists have used a sophisticated metric to identify the world’s most irreplaceable animals—from the aye-aye to the axolotl—while the botanical world remained largely invisible to the same analysis. That changed this spring with a sweeping new study in the journal Science, which reveals that more than 21 percent of the evolutionary history carried by Earth’s flowering plants is now at risk of being lost.
The research, led by Félix Forest of the Royal Botanic Gardens, Kew, along with teams from the Zoological Society of London, Boise State University, and international collaborators, represents the largest species-prioritization assessment ever conducted. The team applied the EDGE metric—short for Evolutionarily Distinct and Globally Endangered—to all 335,497 known species of angiosperms, or flowering plants, cross-referencing molecular data with extinction risk from the IUCN Red List.
A Metric Built for Animals, Turned on the Garden
The EDGE framework, developed by the Zoological Society of London in 2007, ranks species by combining how genetically unique they are within the tree of life with how close they are to extinction. For nearly 20 years, it has highlighted overlooked animals such as the pangolin and the axolotl—creatures that may not headline nature documentaries but represent entire, irreplaceable evolutionary branches.
Rikki Gumbs of the Zoological Society of London, a co-leader of the analysis, noted the historical imbalance: plants were often dismissed as mere “backdrop for photographs of bees and tigers.” The gap was not due to a lack of ecological stakes but a data problem. Assessing extinction risk for roughly 335,000 species of flowering plants—more than ten times the number of ray-finned fish, the largest animal group previously assessed—was a task of staggering scale.
Forest described compiling comparable data for angiosperms as “no small task,” but said the resulting scores now provide vital information to spotlight irreplaceable, threatened species that conservation efforts have often overlooked.
The Number That Should Worry Us: 21.2 Percent
The headline figure is stark: the team estimates that 21.2 percent of angiosperm evolutionary history is at risk of extinction. They identified 9,945 “EDGE species” that disproportionately account for that threatened diversity. For comparison, the equivalent risk across jawed vertebrates—including sharks, birds, and elephants—sits at roughly 13 percent.
These 9,945 species represent only about 3 percent of all known flowering plants, but their evolutionary weight is disproportionate. Losing them would erase branches of the plant tree of life that took tens of millions of years to grow and cannot be recovered.
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 percent of vertebrate groups. “Plants have been dying in the dark,” Buerki said.
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 flavor, now sits alongside the corpse flower’s malodorous relatives among species marked for urgent attention.
One of the more striking cases is the jellyfish tree, or Medusagyne oppositifolia. Found only on a handful of rocky outcrops on the Seychelles’ island of Mahé, it was believed extinct until a few surviving individuals were rediscovered in the 1970s. It is the sole member of its genus, with fewer than 100 mature trees thought to survive in the wild. Its loss would prune an entire limb from the angiosperm family tree.
Another standout is Amborella trichopoda, a modest shrub native to New Caledonia whose evolutionary lineage split from all other flowering plants some 130 million years ago. By the study’s measure, it is the single most evolutionarily distinct angiosperm alive today.
A Roadmap, Not Just an Obituary
The authors frame their findings as a tool for triage rather than a eulogy. The researchers calculate that protecting just 5.9 percent of species, selected by EDGE ranking, would safeguard half of all threatened angiosperm evolutionary history. Protecting the full EDGE list would preserve 16.6 percent of it.
“With finite conservation budgets and infinite need, EDGE scores offer a way to triage resources toward the species whose loss would cost evolutionary history the most,” said Buerki. His team aims 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, the metric has already begun shaping decisions inside the institution’s Living Collections, guiding which specimens horticulturists prioritize for cultivation and seed-banking.
Why It Matters Beyond the Greenhouse
The study’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 worth protecting, yet plants were left out of the assessments meant to operationalize that principle.
“That taxonomic imbalance has undermined plant conservation for decades,” the authors write, “even though the preservation of evolutionary lineages underpins both the immediate benefits people draw from ecosystems and the future of life on Earth more broadly.”
It is a reminder that the animals typically pictured on conservation reports—pandas, polar bears, tigers—depend, ultimately, on the quieter, rootier world sustaining them. As Gumbs put it: “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.”