Mycorrhizal fungi help regulate the Earth's climate and ecosystems by forming underground networks that provide plants with essential nutrients, while drawing carbon deep into soils. Scientists and conservationists have been racing to find ways to protect these underground fungi, but they keep finding dark taxa—species that are known only by their DNA sequences that can't be linked to named or described species.

It is estimated that only 155,000 of the roughly 2–3 million fungal species on the planet have been formally described. Now, a review published in Current Biology shows that as much as 83% of ectomycorrhizal species are so-called dark taxa.