In the complex web of life beneath our feet, mycorrhizal fungi play an indispensable yet largely inscrutable role. By forming intricate underground networks, these fungi facilitate nutrient exchange with plant roots, enhance soil carbon storage, and contribute significantly to the regulation of Earth’s climate. Yet, despite their critical ecological functions, the majority of these fungal species remain shrouded in mystery. A groundbreaking review published in Current Biology on June 9, 2025, highlights the staggering reality that up to 83% of ectomycorrhizal fungi—one of the most widespread fungal groups—belong to what scientists term “dark taxa.” These invisible lineages are identified solely by environmental DNA sequences, without any physical specimens or formal scientific names, posing profound challenges for conservation and ecological research.
Ectomycorrhizal fungi form symbiotic associations with roughly a quarter of all terrestrial vegetation worldwide, a partnership that fuels critical biochemical cycles. Their underground hyphal networks not only ferry essential nutrients like nitrogen and phosphorus to plants but also sequester vast amounts of carbon by transporting it into deep soil layers. Estimates suggest these fungi are responsible for the annual drawdown of more than nine billion tons of atmospheric CO₂, equating to over 25% of global fossil fuel emissions—a staggering ecosystem service that underscores their climate relevance. Despite this, our catalog of described fungal species remains woefully incomplete. Current estimates indicate only about 155,000 fungal species have been formally described, a fraction of the 2 to 3 million species believed to inhabit the Earth.
The primary obstacle to understanding this subterranean biodiversity lies in the prevalence of “dark taxa,” fungal groups identifiable only through sequences of environmental DNA (eDNA) extracted from soil and root samples. Modern sequencing technologies allow scientists to detect these DNA fragments shed by organisms into their surroundings, but the process of linking DNA sequences to known species depends on existing reference databases. Unfortunately, the majority of fungal eDNA sequences lack corresponding, named species in these databases. As a result, researchers encounter strings of nucleotides—As, Ts, Cs, and Gs—that betray an organism’s existence but provide no avenue for classical taxonomic classification.
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Lead author Laura van Galen, a microbial ecologist associated with the Society for the Protection of Underground Networks (SPUN) and ETH University in Switzerland, captures the dilemma succinctly: “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?” This paradox illuminates a critical gap in biodiversity protection—undocumented species that underpin fundamental ecosystem processes remain invisible to policymakers and conservation frameworks predicated on formal taxonomic recognition.
The biogeography of these dark taxa is equally revealing. The review identifies discrete global hotspots where unknown ectomycorrhizal species cluster, specifically tropical forests in Southeast Asia, Central and South America, as well as tropical shrublands in central Africa. Additional hotspots include the montane conifer forests of the Sayan Mountains above Mongolia and other understudied mid-latitude and southern-hemisphere regions. These findings disrupt the traditional ecological paradigm that has disproportionately focused on temperate northern ecosystems. There is an urgent need to redistribute scientific resources and funding to these biodiverse, yet neglected, regions where fungal diversity—and thus ecosystem resilience—may be most vulnerable.
The ramifications for conservation are profound. Many of the plants dependent on ectomycorrhizal fungi are themselves categorized as endangered, a sobering reminder of the interconnectedness of life. The potential loss of host plants inevitably jeopardizes their fungal partners, many of which are essential to soil health, nutrient cycling, and carbon sequestration. Van Galen warns, “If we lose these host plants, we might also be losing really important fungal communities that we don’t know anything about yet.” This cascade effect underscores the intrinsic value of fungi in maintaining biodiversity and ecosystem services.
Addressing this invisible fungal frontier requires innovative approaches. The researchers advocate for increased collection, morphological study, and genomic sequencing of mushrooms and fungal specimens. Co-author Camille Truong of SPUN and the Royal Botanic Gardens Victoria highlights a low-hanging fruit: “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.” This strategy offers a rapid, cost-effective pathway to expand fungal reference databases that can transform unidentified eDNA into named entities, a cornerstone for integrating fungi into conservation policies.
The technological tools underpinning this effort are mature and accessible. High-throughput DNA sequencing, advanced bioinformatics pipelines, and global data-sharing platforms provide an unprecedented capacity to profile soil fungal communities in situ. Yet, despite these advancements, fungi remain conspicuously overlooked in global conservation and climate agendas. The call to action is clear: elevate fungal biodiversity to the same level of importance as plants and animals in ecological research, environmental monitoring, and policy making.
SPUN’s mission exemplifies this paradigm shift. The non-profit scientific organization aims to map and safeguard Earth’s fungal networks in collaboration with local researchers and communities, focusing especially on regions harboring high concentrations of undocumented fungi. Through these partnerships, SPUN seeks to fill critical knowledge gaps and advocate for the inclusion of fungi in climate and conservation strategies worldwide. Their work highlights the ecological significance of subterranean biodiversity and the urgent need to protect these cryptic yet essential life forms.
In synthesizing this review’s insights, it becomes evident that naming and documenting fungal species is not merely a taxonomic exercise; it is foundational to preserving ecosystem functions that sustain human and planetary health. Without clear identification and understanding, conservation efforts risk overlooking key organisms that stabilize soils, promote plant growth, and mitigate climate change through carbon sequestration. The invisibility of dark taxa thus represents both a scientific frontier and a critical conservation blind spot demanding immediate attention.
The discovery of global hotspots teeming with undescribed ectomycorrhizal fungi also reframes our understanding of biodiversity patterns. Tropical forests and understudied montane regions emerge as reservoirs of fungal diversity that could harbor novel species, metabolic pathways, and ecological interactions. Unveiling these hidden communities could yield breakthroughs not only in ecology but also in biotechnology, medicine, and agriculture.
As the scientific community advances toward a more comprehensive catalog of Earth’s fungi, the review underscores a vital principle: conservation is necessarily tied to knowledge. Protecting fungi without their formal recognition is practically and legally challenging; thus, expanding the fungal species’ registry becomes an ethical imperative. Bridging the knowledge gap will require cross-disciplinary collaboration, enhanced funding, and inclusive capacity-building among scientists in the Global South, where fungal diversity is richest but research infrastructure often lags.
In conclusion, the review published in Current Biology charts a new trajectory for mycology and conservation science. It reveals that a vast majority of Earth’s ectomycorrhizal fungi remain hidden in the shadows of taxonomy, detected only through environmental DNA signatures without formal names or descriptions. This “dark taxa” phenomenon not only complicates biodiversity assessments but threatens to exclude fungi from much-needed conservation policies despite their ecological indispensability. Bringing these organisms into the light through strategic sequencing, taxonomy, and global collaboration is essential for safeguarding Earth’s climate, biodiversity, and the health of ecosystems that humanity depends upon.
Subject of Research: Not applicable
Article Title: The biogeography and conservation of Earth’s ‘dark’ ectomycorrhizal fungi
News Publication Date: 9-Jun-2025
Web References:
https://spun.earth/
http://dx.doi.org/10.1016/j.cub.2025.03.079
Image Credits: Adriana Corrales/SPUN
Keywords:
Mycorrhizal fungi, Mycology, Ecology, Applied ecology, Biodiversity, Conservation ecology
Tags: biodiversity of underground lifecarbon drawdown by fungiclimate regulation by fungiconservation challenges of dark taxadark taxa in ecosystemsecological role of fungiectomycorrhizal fungi importanceenvironmental DNA in fungiMycorrhizal funginutrient exchange in ecosystemssoil carbon storageunderground fungal networks