When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse.

In ascomycetes and basidiomycetes, the fusion of two haploid cells forms an intermediate stage called the dikaryotic stage. In this stage, one cell has two diploid nuclei. This stage is called dikaryophase. Later, the parental nuclei fuse, and the cells become diploid. Asexual spores are generally not seen in basidiomycetes, and they generally undergo fragmentation. Thus, basidiomycetes is the group in which asexual spores are generally not seen but dikaryophase is seen. Albugo belongs to phycomycetes, Claviceps belongs to ascomycetes, Alternaria belongs to deuteromycetes, and Agaricus (mushroom) belongs to basidiomycetes.