Key takeaways:
- New research finds more than a fifth of flowering plant evolutionary history could vanish without adequate protection measures in place
- From the "world's smelliest plant" to the tiniest of waterlilies, scientists identify almost 10,000 Evolutionarily Distinct and Globally Endangered (EDGE) species
- This first assessment of its kind for flowering plants will feed into the tree of life indicators of the Global Biodiversity Framework (GBF)
In a new study published today in the journal Science , researchers from the Royal Botanic Gardens, Kew, ZSL (Zoological Society of London) and their international collaborators including Boise State University present the first global assessment of risk to the angiosperm (flowering plants) tree of life, warning that more than a fifth of all angiosperm evolutionary history is at risk of extinction.
The new findings will enable scientists to prioritise many of these vulnerable plants for conservation, giving some of the most truly unique wonders of nature a better chance of survival.
Evolutionary history depicts how living organisms relate to one another on the tree of life and how they change over time. Not all species are equal in evolutionary terms, and some exist on long and isolated branches with few or no close relatives. These species represent a more unique evolutionary history than recently diverged species with several close relatives.
Examples include the shrub Amborella trichopoda, which represent a lineage that is estimated to have split from all other flowering plants about 130 million years ago, and the maidenhair tree, Ginkgo biloba, which is the only known descendant of an ancient lineage dating back more than 300 million years.
To determine how much evolutionary history is presently at risk of extinction, the scientists used a metric known as EDGE or "Evolutionarily Distinct and Globally Endangered." The metric, introduced by ZSL in 2007, combines the extinction risk faced by an individual species with how genetically distinct it is within the wider tree of life.
The findings indicate that more than a fifth (21.2%) of angiosperm evolutionary history is at risk of extinction, nearly double that of jawed vertebrates (13%). The authors have also identified 9,945 EDGE species, about 3% of all known flowering plant species, each representing a large proportion of unique and threatened evolutionary history, marking them as priorities for conservation.
EDGE scores for all 335,497 flowering plant species were assigned using molecular data and the IUCN Red List of Threatened Species - making it the single largest species prioritisation assessment in the history of conservation. Computer modelling was then used to fill the gaps in the IUCN data and predict the extinction risk of species unassessed by the Red List, as at the time of the analysis, only about 20% of flowering plants had Red List assessments.
Protecting just 5.9% of species ranked by their EDGE score would protect half of all angiosperm threatened evolutionary history, while protecting all EDGE species would protect 16.6% of threatened angiosperm evolutionary history.
At Kew, the EDGE metric is already being used by horticulturists as a decision-making tool in the curation of the extensive Living Collections.
Félix Forest, Senior Research Leader in Spatial Phylogenetics at Kew, who led the study, said: "Given that there is more than 10 times the number of species in angiosperms than what is found in the largest animal group for which EDGE scores have been compiled so far, the ray-finned fish, compiling this crucial information for flowering plants was no small task.
'These EDGE scores provide the vital information required to highlight the irreplaceable and threatened species that are often overlooked and whose conservation will help maintain current and future benefits to people and the future of all life on Earth.
'And what are we going to focus on next? Ferns and lycopods!"
Findings will be open and accessible on Flora of the World
Research co-author Sven Buerki from Boise State University was a member of Félix Forest's research group at the Royal Botanic Gardens, Kew, where he helped lay the foundations for this work. As the Dr. Davidson Endowed Chair of Botany at Boise State University, Buerki will translate the findings into accessible, open conservation data hosted on Flora of the World .
A key contribution of Buerki's work at Boise State has been to cross-reference the EDGE dataset against Flora of the World's global occurrence database. The analysis reveals that 229 of the 9,945 EDGE list species (2.3%) are already documented in Flora of the World — with specimen and observation records pinpointing exactly where these plants have been collected in the wild. These 229 species span remarkable diversity, from the Critically Endangered Amorphophallus lewallei of the Congo Basin (ranked 2nd globally for EDGE score) to island endemics like Ilex dimorphophylla from Japan's Ryukyu Islands.
In total, the Flora of the World species with EDGE data collectively represent approximately 44,418 million years of angiosperm evolutionary history — 4.4% of all flowering plant ED on Earth. Among matched species, exceptional outliers stand out: Gomortega keule (78 Myr), the sole member of its family, survives in a single valley in Chile; and Cephalotus follicularis (76 Myr), a carnivorous pitcher plant from a single coastal habitat in Western Australia, represents one of the most isolated lineages in the plant kingdom.
Extinct in the Wild: The most urgent conservation cases
Among the species with EDGE scores documented in Flora of the World, four carry the most sobering designation on the International Union for Conservation of Nature Red List: Extinct in the Wild. These are plants that no longer exist as self-sustaining populations in nature — their survival depends entirely on cultivation in botanical gardens, seed banks, and similar ex situ collections. They are Franklinia alatamaha , Brugmansia suaveolens , Brugmansia vulcanicola , and Brugmansia sanguinea .
The three Brugmansia species (angel's trumpets) represent a genus now considered entirely Extinct in the Wild. Once cultivated by Andean communities for centuries, these plants are no longer found in unmanaged natural populations. Franklinia alatamaha, a flowering tree from Georgia in the United States, was last seen in the wild in 1803 and survives today solely through material preserved by early American botanists. Flora of the World's documentation of these species links their occurrence records directly to the EDGE framework, making their conservation status visible to a global audience.
Buerki said: "Our goal at Boise State is to make the results of this study directly visible in Flora of the World — so that anyone exploring a species page can see not just where a plant has been recorded, but how evolutionarily unique and how threatened it is. Embedding EDGE scores into the platform is central to the mission of the Davidson Endowment, and it is the work we are committed to completing.
