Basidiomycota A phylum of fungi, formerly classified as a class (Basidiomycetes) or a subdivision (Basidiomycotina). Sexual reproduction is by means of basidiospores produced externally on a club-shaped or cylindrical basidium. Basidia are often grouped together on fruiting structures, such as mushrooms, puffballs, and bracket fungi. Exceptions are the rusts and smuts, which do not produce obvious fruiting bodies.

basidium A microscopic structure upon which sexually produced spores are formed externally. Basidia are characteristic of fungi of the Basidiomycotina.

basidium (pl. basidia) A specialized cell in fungi of the phylum Basidiomycota, in which nuclear fission and meiosis occur. This results in the formation of four basidiospores, which are attached to the basidium by means of sterigmata (short stalks).