Phylogenetic placement of the secotioid fungus Araneosa columellata within Agaricus

Recently collected material was used to evaluate the phylogenetic position of the secotioid fungus Araneosa columellata. We amplified the nuclear ribosomal RNA gene (ITS1, ITS2, and LSU) and found Ar. columellata to be a member of the genus Agaricus (Agaricaceae, Agaricales), necessitating its transfer to that genus as Agaricus columellatus comb. nov. A detailed description is provided along with illustrations, and a lectotype is designated.