The dikaryon is a nuclear feature which is unique to some fungi, in which after plasmogamy the two compatible nuclei of two cells pair off and cohabit without karyogamy within the cells of the hyphae, synchronously dividing so that pairs are maintained in the older cells while newer cells or hyphal tips are also binucleate, i.e. dikaryotic; in the Ascomycota this attribute of the nuclei to do such is only found in the Ascogenous hyphae but is the dominant phase in the Basidiomycota. The formation of a dikaryon is a plesiomorphic character for the subkingdom Dikarya, which covers both the Basidiomycota and Ascomycota. The formation of croziers in the Ascomycota and of clamp connections in the Basidiomycota facilitate maintenance of the dikaryons. However, some fungi in each of these phyla have evolved other methods for maintaining the dikaryons, and therefore neither croziers nor clamp connections are ubiquitous in either phylum.
The name dikaryon comes from the Greek words δι (di) meaning "two" and καρυόν (karyon) meaning "nut", referring to the cell nucleus.