Current knowledge of Chytridiomycota diversity in Northern Europe and future research needs

Chytridiomycota is the most species-rich phylum of basal lineage fungi involved in vital processes in both terrestrial and aquatic ecosystems. Still, the diversity and richness of this group remains cryptic. In Northern Europe, few species have been recorded despite the numerous intact lake systems covering this region. Recent classifications of early diverging fungal lineages differ considerably on the diversity of chytrid species and their taxonomic placement. Here, we present the current knowledge of the Chytridiomycota diversity within Northern Europe by using the Global Biodiversity Information Facility (GBIF) data and compare how this diversity distributes across two recently proposed classification systems. Furthermore, we illustrate how various sampling types are influencing the recorded classification levels. Lastly, we discuss how metabarcoding has contributed to the overall understanding of the Chytridiomycota diversity in revealing the “dark matter fungi”, and we point out future research needs in the field of aquatic mycology in the Nordic region.