Mission impossible completed: unlocking the nomenclature of the largest and most complicated subgenus ofCortinarius,Telamonia

So far approximately 144,000 species of fungi have been named but sequences of the majority of them do not exist in the public databases. Therefore, the quality and coverage of public barcode databases is a bottleneck that hinders the study of fungi.Cortinariusis the largest genus of Agaricales with thousands of species world-wide. The most diverse subgenus inCortinariusisTelamoniaand its species have been considered one of the most taxonomically challenging in the Agaricales. Its high diversity combined with convergent, similar appearing taxa have earned it a reputation of being an impossible group to study. In this study a total of 746 specimens, including 482 type specimens representing 184 species were sequenced. Also, a significant number of old types were successfully sequenced, 105 type specimens were over 50 years old and 18 type specimens over 100 years old. Altogether, 20 epi- or neotypes are proposed for recently commonly used older names. Our study doubles the number of reliable DNA-barcodes of species ofC. subgenusTelamoniain the public sequence databases. This is also the first extensive phylogenetic study of the subgenus. A majority of the sections and species are shown in a phylogenetic context for the first time. Our study shows that nomenclatural problems, even in difficult groups likeC. subgenusTelamonia,can be solved and consequently identification of species based on ITS barcodes becomes an easy task even for non-experts of the genus.