New ITS rDNA barcodes clarify phylogenetic relationships and biogeography of aquatic hyphomycetes

Abstract Aquatic hyphomycetes are key microbial decomposers of allochthonous organic matter in freshwater ecosystems. Although their importance in carbon flow and food webs in streams is widely recognized, there are still gaps in our understanding of their phylogeny, molecular diversity and distribution patterns. Our study utilized the growing database of ITS rDNA barcodes of aquatic hyphomycetes (1252 sequences) and aimed to (i) produce new barcodes for some lesser-known taxa of aquatic hyphomycetes, (ii) clarify the phylogeny of aquatic hyphomycetes, including the placement of some taxa at the class or order level based on molecular data, and (iii) provide insights into biogeography of this group. This study increased the number of aquatic hyphomycetes with available ITS barcode from 120 species (out of ~ 300 species described) to 136 species. Phylogenetically, the 136 species of aquatic hyphomycetes were distributed between two phyla (Ascomycota and Basidiomycota), 6 classes and 10 orders of fungi. However, 36 species remain incertae sedis without attribution at the order level. The geographical distribution of species with available ITS sequences included 50 countries from 5 continents. North American and European countries showed the highest number of aquatic hyphomycete species with ITS barcodes, with 6 countries having more than 20 species: Portugal (34 species), United States of America (33 species), United Kingdom (29 species), Germany (28 species), France (22 species) and Czech Republic (21 species).