Why millions of fungal species still remain unknown

Beneath the forest floor lies a vast and vital network of life – underground fungi that help regulate Earth’s climate and sustain ecosystems by transporting nutrients to plants and locking carbon deep in the soil.

Among these are mycorrhizal fungi, especially ectomycorrhizal species, which form intricate symbiotic relationships with trees and plants. But as scientists try to understand and protect these essential organisms, they’re running into a surprising obstacle: the majority of these fungi remain unknown.

A new study reveals that up to 83% of ectomycorrhizal fungi belong to “dark taxa” – species that have never been formally named or described. Scientists only know these organisms through fragments of their DNA, and their anonymity poses a significant challenge for conservation.

Invisible fungal diversity

Only about 155,000 fungal species have been officially documented, while scientists estimate that between two and three million exist. In recent years, environmental DNA (eDNA) sampling – extracting genetic material directly from soil and roots – has helped researchers detect many more species.

However, for most of these mysterious fungi, there’s no existing match in the scientific record.

Laura van Galen is lead author of the study and a microbial ecologist working with the Society for the Protection of Underground Networks (SPUN) and ETH Zurich.

“We are a long way out from getting all fungal DNA sequences linked to named species,” she said. “Environmental DNA has enormous potential as a research tool to detect fungal species, but we can’t include unnamed species in conservation initiatives. How can you protect something that hasn’t yet been named?”

Traditionally, scientists assign described species Latin binomials – names that help them track and study these organisms. Without these identifiers, dark taxa remain excluded from conservation frameworks.

Fungi drive forest health

Ectomycorrhizal fungi are more than obscure soil residents – they’re powerhouses of planetary health.

These fungi partner with roughly a quarter of all plant life and play an outsized role in Earth’s carbon cycle, drawing down over nine billion tons of carbon dioxide each year.

That’s more than 25% of the CO2 released annually by fossil fuels. They also help regulate nutrient flows in forests, support plant resilience, and even break down pollutants.

Tropics hold untapped fungi

Despite their importance, most ectomycorrhizal research focuses on the Global North, leaving tropical fungal communities overlooked.

According to the study, hotspots for dark taxa are especially concentrated in tropical forests and shrublands in Southeast Asia, Central and South America, and parts of Africa. They also occur in montane forests above Mongolia.

“Mid-latitude and southern-hemisphere regions show signs of being home to many unknown species,” said van Galen.

“This means there is a mismatch in resources and funding. We need to facilitate more tropical researchers and those from southern-hemisphere regions to focus on identifying these super-important fungi.”

Naming the nameless

To bring these fungi into the scientific spotlight, the researchers suggest two main strategies: fieldwork and museum science. Collecting and sequencing new fungal samples is vital, but revisiting existing collections is equally important.

Camille Truong is co-author of the study and a mycorrhizal ecologist at SPUN and the Royal Botanic Gardens Victoria in Australia.

“One way to reduce the dark taxa problem is to collect, study and sequence mushrooms and other fungi,” said Truong.

“Conversely, there are mushrooms that have been sitting for decades in collections of botanical gardens. These should be urgently sequenced so that we can, hopefully, start matching them up with some of these dark taxa.”

The stakes are high. Many of these unknown fungi are linked to plant species that are themselves endangered. If those plants disappear, their fungal partners – possibly with vital ecological functions – could vanish without ever being documented.

“We’re at risk here,” van Galen warned. “If we lose these host plants, we might also be losing really important fungal communities that we don’t know anything about yet.”

Prioritizing underground fungal species

The tools to explore fungal diversity already exist. What’s missing is widespread recognition of the fungi’s role in climate and biodiversity, and a coordinated push to study and protect them.

“We really need to pay so much more attention to fungi in the soil so that we can understand the species and protect them and conserve them before we lose them,” van Galen said.

The authors hope their research will help steer conservation organizations toward prioritizing regions rich in underground fungal diversity – even if the species found there are still nameless.

After all, in the quiet depths of the soil, scientists may discover the foundations of forests, climate stability, and even our future.

The study is published in the journal Current Biology.

Image Credit: Adriana Corrales/SPUN

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