The lichen symbiont Wadeana represents an independent origin of hysterothecial fungi in the Eurotiomycetes.

The genus Wadeana was erected almost fifty years ago to accommodate an unusual pair of lichen fungal symbionts with hysterothecial ascomata and polysporous asci associated with the algal genus Trentepohlia. The evolutionary position of Wadeana has long been unclear, and the genus has variably been treated as a dothideomycete, as incertae sedis or, recently, within the subclass Acarosporomycetidae of the Lecanoromycetes. Here we present multilocus evidence from metagenome-assembled genomes from the generitype, Wadeana dendrographa, that place it with strong support as sister to all genera currently treated in the order Sclerococcales in the subclass Sclerococcomycetidae of the Eurotiomycetes. Wadeana represents the first confirmed case of hysterothecial ascomata in Eurotiomycetes. We compare evidence for its status as a lichen symbiosis with examples of fungal-algal interactions in other members of the Sclerococcomycetidae. Finally, we also describe a new family (Wadeanaceae) and order (Wadeanales) to accommodate Wadeana and a new subclass (Xylobotryomycetidae) to accommodate the order Xylobotryales in the Eurotiomycetes.