The Mixiomycetes are class of fungi in the Pucciniomycotina subdivision of the Basidiomycota. The class contains a single order, the Mixiales, which in turn contains a single family, the Mixiaceae that circumscribes the monotypic genus Mixia. Only one species has been described to date, Mixia osmundae; this species was originally named Taphrina osmundae by Japanese mycologist Toji Nishida in 1911. It is characterized by having multinucleate hyphae, and by producing multiple spores on sporogenous cells.