Nature on the EDGE of extinction: Kew and ZSL scientists warn 21% of flowering plant evolutionary history is at risk

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 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.  

Dr 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!’ 

Unique species on the EDGE of extinction 

The top-ranked EDGE angiosperm identified in the study was Hondurodendron urceolatum, a dioecious tree with a few scattered populations found across a single mountain range in the Parque Nacional El Cusuco, Honduras. 

Other top-ranked EDGE species include the ‘world’s smelliest plant’ (Amorphophallus titanum) and several of its relatives, the jellyfish tree (Medusagyne oppositifolia) from the Seychelles, and the succulent annual Kewa acida, and several species of Magnolia.  

The EDGE list also includes many plants with known uses for humanity, such as Vanilla planifolia, a beautiful orchid that is the main source of vanilla globally, and Gomortega keule, the only known species in the family Gomortegaceae with edible fruit and wood used for timber, that is found in a small area on the coast of central Chile. Another iconic EDGE species is the world’s smallest waterlily, Nymphaea thermarum, which is native to thermal hot springs in Rwanda and until 2023 thought to be extinct in the wild due to overexploitation. 

Around 10% of the world’s flowering plants have at least one documented use, and the authors fear that losing these species could have catastrophic consequences, not just for the benefits plants provide humanity today, but for the many undiscovered use they may have.  

Dr Matilda Brown, Kew Research Fellow and study co-lead, said: ‘When we talk about EDGE species as ‘weird and wonderful’, we tend to think of their physical characteristics, whether that's their bizarre, jellyfish-shaped flowers, or their sheer size, but it also includes the things we can't see - their molecules, chemicals and other properties that we as humans depend on.  

‘The benefits that EDGE species provide to society are as unique and irreplaceable as the species themselves, so losing a deep branch of the tree of life means the potential loss of the next breakthrough cancer drug or antibiotic, with no second chance.’ 

The study’s findings will feed into the reporting of tree of life indicators of the Kunming-Montreal Global Biodiversity Framework (GBF), the Phylogenetic Diversity Indicator and the EDGE Index. Prior to this study, it was only possible to report on these indicators for animals and some non-flowering plants (gymnosperms, which include conifers and their relatives). Adopted by 196 parties in 2022, the GBF outlines several key targets for biodiversity protection, including the 30x30 Target to protect at least 30% of the planet’s land and water by 2030. 

Dr Rikki Gumbs, a researcher at ZSL’s Institute of Zoology and study co-lead, said: ‘We’ve been using and refining the EDGE approach for almost two decades, allowing conservationists globally to identify the overlooked animals most in need of urgent conservation action, but armoured anteaters and dancing frogs are just one part of the incredible tree of life that spans across our planet. 

‘Flowers and forests aren’t just a pretty backdrop for pictures of bees and tigers. Each plant is an essential, living building block to life on Earth, providing us with air to breathe and food to eat. By applying the EDGE approach to flowering plants, we are better able to protect our planet’s rich, bustling ecosystems that have taken billions of years to develop.  

‘As ZSL celebrates our 200th anniversary, we’re proud to be leading the way on protecting nature for the next 200 years and beyond.’ 

Since 2007, ZSL’s EDGE of Existence Programme has been championing the underdog and supporting in-country grass-roots conservationists, known as EDGE Fellows, to focus on the conservation of EDGE species – from the Endangered purple frog to the Critically Endangered pygmy three-toed sloth. In partnership with Kew, and with support from of the Franklinia Foundation, 14 EDGE Fellows have been focusing their attention on plants, more specifically gymnosperm tree species. The publication of this study now offers the possibility of expanding the fellowship to angiosperm species. 

Check out EDGE species at Kew 

From 20 May, visitors to Kew Gardens in West London will have a unique opportunity to see several of the EDGE-ranked species on display in one place in the Princess of Wales Conservatory. The exhibition, jointly curated by Kew’s horticulturists and scientists, will take over the glasshouse’s orchid display cabinets, highlighting rare and unusual specimens, many of which are usually kept behind the scenes.  

Some of the rarities on display will include the Critically Endangered Blue Amaryllis or Empress of Brazil (Worsleya procera), the only known species in its genus and one of the rarest members of the Amaryllidaceae family, found only in mountains around Petropolis in Brazil.  

Visitors will also get to see the vulcan palm (Brighamia insignis), originally endemic to the islands of Kauaʻi and Niʻihau in Hawaii, but now extinct in the wild since 2020. And be sure to keep an eye out for the Albany pitcher plant (Cephalotus follicularis) from Western Australia, which is the only known member of the family Cephalotaceae. 

Within Kew’s Living Collections of more than 16,500 species of plants, 455 angiosperms and 75 gymnosperms have been identified as EDGE species. These numbers highlight the important role botanic gardens play in preserving global plant diversity ex situ, at a time of ever-increasing environmental challenges and climate change. 

Tom Pickering, Head of Glasshouses Collections, said: ‘The goal of this exhibition is to show our visitors that botanic gardens hold valuable living collections of conservation importance. Global biodiversity is vanishing before our eyes, and some of the most remarkable plant species on Earth face an uncertain future.  

‘Growing these species helps us to better understand them and may hold the key to preventing their extinction. We have demonstrated that this can be done, but the urgency to do more is pressing. 

‘By visiting Kew you directly support our mission to build a thriving planet for all. I also would encourage anyone visiting to Kew to visit this exhibition in the Princess of Wales Conservatory and learn about these unique, spectacular and rare plant species.’ 

Amongst the many other EDGE species publicly on display or behind the scenes in Kew’s nurseries, are rare icons like the Pseudohydrosme gabunensis, an endangered plant renowned for its foul smell that flowered for the first time in the UK in 2025.  

The collections also include the aquatic waterwheel plant, Aldrovanda vesiculosa, which captures small aquatic invertebrates using traps similar to the Venus flytrap; the carnivorous Roridula gorgonias from South Africa; Franklinia alatamaha, which is extinct in the wild but lives on in cultivation; and Tahina spectabilis, the suicide palm from Madagascar, which lives up to 50 years, before producing a huge inflorescence and dying.  

Other examples include Myrcia neothomasiana, found only on three Caribbean islands, and the giant quiver tree (Aloidendron pillansii), a large and Critically Endangered succulent found around the border of Namibia and South Africa. 

In the nearby Davies Alpine House, which celebrated its 20th anniversary this spring, you will find a flowering Hartweg's doll's-lily (Odontostomum hartwegii), the only known representative of its genus. This wildflower is endemic to Northern California, found along the north and central Sierra Nevada foothills and other areas. 

Visitors can also see four of the highest-ranking EDGE species of gymnosperm near the Orangery. These are the maidenhair tree (Ginkgo biloba) and a Wollemi pine (Wollemia nobilis), both planted by the late Queen Elizabeth II and Duke of Edinburgh to celebrate Kew’s 250th anniversary in 2009. Nearby you can also spot an imposing monkey puzzle tree (Araucaria araucana), as well as large Atlas cedar (Cedrus atlantica).  

And if you venture out into the lawns outside the Orangery, you will come across another special Wollemi pine that was planted back in 2005 by Sir David Attenborough who is celebrating his 100th birthday this week. 

ENDS