Another dark taxon comes to light: Semicentenialomycetes, a new class within the Pucciniomycotina (Basidiomycota), and its described living representative, Semicentenialea rex doi-10-17044-scilifelab-26894242-0 https://doi.org/10.17044/SCILIFELAB.26894242 Swedish National Data Service Svensk nationell datatjänst Landing page Another dark taxon comes to light: Semicentenialomycetes, a new class within the Pucciniomycotina (Basidiomycota), and its described living representative, Semicentenialea rex doi-10-17044-scilifelab-26894242-0 https://doi.org/10.17044/SCILIFELAB.26894242 Rosling, Anna Swedish National Data Service Svensk nationell datatjänst Landing page Only a small fraction of the world’s fungi is described, and a large number of fungal sequences from environmental DNA (eDNA) currently lack relevant reference sequences for taxonomic identification in metabarcoding studies. Partially because there are several deeply divergent fungal lineages, including hypothesized class- and order-level lineages, currently known only by eDNA sequences. Here, we describe the first living representative of one such lineage (previously referred to as Clade GS25). We use a phylogenomic approach to test the placement and taxonomic rank hypothesized for this lineage, and present the formally described Semicentenialea rex, as the first known species in the novel class Semicentenialomycetes (Pucciniomycotina, Basidiomycota). Additionally, we provide the first phylogenomic resolution of Pucciniomycotina, using reference genomes from all described classes with the exception of Cryptomycocolacomycetes. We propose a set of practices that could be adopted by the research community to help facilitate more connections between living fungi and eDNA sequences. The use of such practices would in turn help to alleviate some of the complications associated with fungal DNA sequences in reference databases and contribute towards a more complete understanding of fungal diversity. Access to data through an external actor. Åtkomst till data via extern aktör.