Fungi are fundamental to all aspects of terrestrial ecosystem function, and influence nutrient cycling, plant health, and ecological processes in wild and domesticated communities on which all aspects of human sustainability depend. However, fungi are under-studied compared to plants and animals: in the most comprehensive trees of life published so far, fungi occupy only a sliver of the represented phylogenetic space. Yet, fungal biodiversity likely exceeds that of plants and animals.
Ecological interactions between fungi and photosynthetic organisms (cyanobacteria, algae, and embryophytes) represent a central mechanism underlying the immense macroevolutionary success of fungi and plants, which in turn has transformed terrestrial landscapes over evolutionary timeframes. Current perspectives on fungal-autotroph interactions focus primarily on plant-pathogenic, lichenized, and mycorrhizal fungi, but recent advances indicate that these represent only a subset of functional, physiological, genetic, and phylogenetic diversity in the fungal kingdom. The ‘unknown’ components of the fungal tree not only frame these best-known fungal symbioses with an evolutionary and ecological context, but also comprise important functional, ecological, and evolutionary dynamics that are fundamental to the productivity, community structure, and evolution of photoautotrophic organisms.