Comparison of the protologue of Agaricus umbellifer L. with specimens and descriptions of the basidiolichen Lichenomphalia umbellifera (L.) Redhead & al. revealed that the epithet umbellifera was misapplied to the Lichenomphalia species, causing several major conflicts with Linnaeus’s species concept. A felicitous match for Linnaeus’s species concept was found with a species of Marasmius sect. Epiphylli. Because A. umbellifer falls in a group that arises from an evolutionary pathway divergent from that leading to Marasmius s. str., we erected a new genus, Owingsia, to accommodate it, and recombined the type species as Owingsia umbellifera. Molecular studies demonstrated that it is a widely distributed circumpolar species, prevalent in Lapland and islands of the Baltic Sea, where Linnaeus encountered it. The earliest legitimate description of the basidiolichen L. umbellifera is A. pseudoandrosaceus Bull., a name superseded by the sanctioned later synonym, A. ericetorum Pers. We recombined this basionym as L. ericetorum, and epitypified O. umbellifera and L. ericetorum with modern sequenced specimens. Key words—nomenclature, taxonomy.