More than 2m fungi species are waiting to be identified around the world in what scientists have called “a new frontier of discovery” for life on Earth, according to a new report. But researchers also warn that the vast majority of new plant discoveries are endangered species, which should be listed as threatened with extinction by default, warning that three-quarters of undescribed species are likely to be at risk of disappearing. From the residents of the human microbiome to the largest known terrestrial organism on the planet, fungi are second only to invertebrates in their diversity – they are found in the air, inside plants and animals, and in the soil and ocean, in many shapes and sizes. More than 90% of them remain unknown to science, according to researchers at the Royal Botanic Gardens, Kew, who have released a new estimate of fungi diversity as part of a report on the health of the world’s plants and fungi, finding that there are probably about 2.5m species with only 155,000 identified so far. “This is uncharted territory,” said Prof Alexandre Antonelli, director of science at RBG Kew. “Over the last few years, we’ve seen an increasing appreciation for the role of fungi in everything … They are sustaining our life, our vegetation, they are absolutely crucial for every single animal species. “Now we have DNA analysis, we are trying to push frontiers. It’s quite similar thing to explore the outer universe. Fungi are the dark matter.” Scientists’ excitement at this undiscovered world was tempered by concern at the threat of extinction faced by many newly discovered species. Of the vascular plant species identified in 2020, researchers found more than 77% already met the criteria for threatened, 59% of species were likely to meet the criteria for endangered, and 24% likely to meet the criteria for critically endangered. With 350,000 species of vascular plants known to science, researchers believe about 100,000 are yet to be identified, but as many as one in three of those are likely to be threatened with extinction, the RBG Kew report estimates. The Kew scientists say all newly described species should be treated as being threatened unless it can be shown otherwise. Researchers around the world are encouraging the public to help with their identification efforts, which have been revolutionised by new DNA sequencing techniques that have found hundreds of fungi species in a single teaspoon of soil. In the Netherlands, one scheme offers the public the chance to name any new fungi species found in soil samples they send in to the laboratory. Since 2020, about 10,200 new fungi species have been formally described, but scientific advances mean that researchers are hopeful they could identify 50,000 new fungi species a year. This year, Kew researchers said they had found a new parasitic fungus that preys on trapdoor spiders in Brazil’s Atlantic rainforest, similar to zombie-ant fungi, which overcome the insects and trick them into leaving their nests to go to places where they can spread their spores. Ester Gaya, a senior researcher at RBG Kew focused on fungi, said she was hopeful that identifying more species could lead to advances in medicine, agriculture and engineering, as well as helping better understand human diseases. “DNA techniques have revolutionised fungi research, much more than plants and animals. Initially we were only looking at mushrooms and lichens,” she said. “Now, it’s the gut microbiome. Many, many human diseases now are shown to be caused by fungus or by an imbalance in your fungal community. Fungi underground connect trees and establish symbiotic relationships with the roots of trees and they exchange nutrients and water. You are breathing spores of fungi right now.” The report says identifying and describing new plant and fungi species is a crucial challenge for biodiversity science. Researchers highlighted 32 plant diversity “darkspots” where there are critical knowledge gaps, with Colombia, New Guinea and south-central China having the greatest shortfalls. “The problem is that we have lots of knowledge gaps. We have lots of places around the world where we have not yet collected enough [plants] or collected a very biased proportion of the biodiversity,” Antonelli said. “The idea [with darkspots] was really to identify those areas where we can get the most cost benefits. The biggest reward systems of new scientific discoveries.”