Bartheletia paradoxa, a basidiomycete growing on fallen leaves of Ginkgo biloba, is redescribed. In autumn a rapidly developing anamorph is formed on freshly fallen leaves and subsequently a teleomorph with hemispherical pustules of thick-walled resting spores (teliospores) that germinate after a resting period of one year with stipitate, longitudinally septate, statismosporic phragmobasidia. The basidia produce several basidiospores on each sporogenous locus. Inoculation experiments and observations in the field suggest that the basidiospores infect the freshly fallen leaves of G. biloba so that the life cycle is completed. The extraordinarily rapid development has also been confirmed in cultures on agar media and in inoculation experiments. Inoculation experiments also indicate that the fungus is specific to G. biloba. The septa of the hyphae have no central pores, but multiple plasmodesma-like perforations. The basidiospores and conidia are uninucleate, but an assessment of the karyology is still pending. A molecular phylogenetic hypothesis based on nuSSU rDNA sequences suggests that the fungus belongs to the Agaricomycotina, clustering in an unresolved position at the basal branching of the group. The family Bartheletiaceae fam. nov. is proposed to accommodate Bartheletia paradoxa in the Agaricomycotina. The name B. paradoxa is validated by a Latin diagnosis and by the designation of types.