The evolution of ectomycorrhizal symbiosis in the Late Cretaceous is a key driver of explosive diversification in Agaricomycetes

Ectomycorrhizal (EcM) symbiosis is one of the most ubiquitous and important plant–microbe interactions in forest ecosystems. Coevolutionary interactions often create new ecological opportunities for explosive diversification. It remains unclear why the evolution of EcM fungi did not necessarily increase ecological opportunities for explosive diversification. This study aims to reveal the driving mechanism of the explosive diversification in the fungal class Agaricomycetes, specifically by testing whether the evolution of EcM symbiosis in the Late Cretaceous increased ecological opportunities. Molecular phylogenies of Agaricomycetes inferred from fragments of 89 single-copy genes indicate that the unidirectional evolution of EcM symbiosis occurred multiple times, ranging in date from the early Triassic to the early Paleogene. However, five analyses for estimating net diversification rates (speciation rates minus extinction rates) suggest that the explosive diversification occurred only a...