Ectomycorrhizal fungi (EcMF) are the key symbionts of numerous woody plants in many ecosystems worldwide. In this study, we explored the diversity of EcMF species introductions based on literature review and our own unpublished data from all continents. We showed that the relative numbers of naturalized EcMF species are higher in EcMF lineages with prevalence in early successional stages. In total, 130 co-introduced EcM fungal SHs associated with roots of alien EcM plants were recorded in 57 analysed datasets worldwide. The introductions are also probably on the rise due to increasing global trade and planting exotic material in attempts to counteract climate change effects on native trees. The richness of naturalized species largely differed among EcMF lineages.