Fungi are organisms that live entirely by the absorption of nutrients from either living or dead organisms. They represent an important component of the ecosystem, where they function as decomposers and in the recycling of carbon and minerals. Thus, fungi played a pivotal role in the establishment of early terrestrial ecosystems. The oldest evidence of life on Earth is septate filaments, like those of certain cyanobacteria, dated at approximately 3.6 billion years.

Evidence of the oldest terrestrial fungi includes hyphae approximately 430 million years old, but it is impossible to determine how these fungi interacted with other organisms in the ancient ecosystem. The oldest fossil fungi in which interactions can be accurately documented are from the Lower Devonian Rhynie Chert, dated at approximately 400 million years.