Fungi Were Shaping Earth Long Before Plants Existed

The fungal kingdom has been quietly rewriting Earth’s early history. New research from the Okinawa Institute of Science and Technology reveals that fungi diversified hundreds of millions of years before land plants emerged, fundamentally challenging our understanding of how terrestrial life began.

The timeline matters because it upends a long-held narrative. We tend to think of plants as the pioneers that made land habitable, with fungi arriving later as helpful partners. The reality appears far more complex, and far older.

Five Paths to Complexity

Complex multicellular life evolved independently exactly five times on Earth: in animals, land plants, fungi, red algae, and brown algae. Each group developed sophisticated mechanisms for cells to specialize, communicate, and organize into tissues. For most of these lineages, fossils provide clear timestamps. Animals appear around 600 million years ago in formations like the Ediacaran, with their distinctive quilted, pancake-like impressions. Land plants show up roughly 470 million years ago as tiny fossilized spores. But fungi present a stubborn puzzle.

Their soft, thread-like bodies rarely fossilize well. Unlike animals or plants, which each evolved complex multicellularity once, fungi developed this trait multiple times from different single-celled ancestors. The fossil record offers only scattered, ambiguous clues.

Reading Genetic Clocks and Gene Swaps

To work around the scarcity of fungal fossils, researchers turned to molecular clocks, measuring genetic mutations that accumulate at relatively steady rates. But molecular clocks need calibration, and that typically requires fossils. The team found an unexpected solution in horizontal gene transfer, rare events where genes jump sideways between distantly related species.

If a gene from lineage A is found to have jumped into lineage B, it establishes a clear rule: the ancestors of lineage A must be older than the descendants of lineage B.

Professor Gergely J. Szollosi, who led the study, explains that identifying 17 such transfers allowed the team to establish “older than/younger than” relationships that tightened the fungal timeline alongside traditional fossil evidence.

The analysis, published in Nature Ecology & Evolution, suggests fungi’s common ancestor dates to roughly 1.4 to 0.9 billion years ago, well before land plants. That timing reveals a long prelude of fungi-algae interactions that helped prepare Earth for terrestrial life.

Fungi run ecosystems, recycling nutrients, partnering with other organisms, and sometimes causing disease. Pinning down their timeline shows fungi were diversifying long before plants, consistent with early partnerships with algae that likely helped pave the way for terrestrial ecosystems.

Co-first author Dr. Lenard L. Szantho emphasizes that this isn’t merely academic history. Understanding when fungi emerged shows they were already present and diversifying for hundreds of millions of years before the first true plants took root.

This revised timeline reframes the story of land colonization entirely. For perhaps 200 to 400 million years before plants appeared, fungi were likely interacting with algae in microbial communities. These ancient fungi may have been Earth’s first ecosystem engineers, breaking down rock, cycling nutrients, and creating primitive soils. Plants didn’t colonize a barren wasteland. They inherited a world fungi had been preparing for eons.

The research grew from collaboration between OIST’s Model-Based Evolutionary Genomics Unit and partners across Europe, including Hungary’s HUN-REN Biological Research Centre, the University of Bristol’s Paleobiology Group, and Spain’s Institute for Research in Biomedicine. The team analyzed 110 fungal species using 225 phylogenetic markers, accounting for compositional quirks in amino acid sequences that can throw off evolutionary reconstructions.

The findings suggest that fungi were diversifying during what scientists once called the “boring billion,” a supposedly quiet interval between 1.8 and 0.8 billion years ago. Increasingly, molecular evidence reveals this era was anything but boring. Major eukaryotic lineages were branching and experimenting with complexity, even if the fossil record captured little of this activity.

What remains uncertain is exactly how early fungi and algae interacted. Did they simply coexist as ecosystem partners, or were they already involved in the complex symbiotic relationships we see today? The oldest unequivocal fossils of mycorrhizae and lichen associations date to only about 400 million years ago, already well into the plant era. Understanding these ancient partnerships will require more work characterizing how modern fungi interact with streptophyte algae, the group that gave rise to land plants.

The study provides a temporal framework for investigating these early interactions and reinforces a growing realization: fungi weren’t supporting players in Earth’s terrestrial drama. They were writing the opening act.

Nature Ecology & Evolution: 10.1038/s41559-025-02851-z