A basidiospore is a reproductive spore produced by Basidiomycete fungi. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. In gills under a cap of one common species in the phylum of Basidiomycota, there exist millions of basidia. Mature state of basidia has the base usually topped with four basidiospores in which contains one from the two haploid nucleus obtained from the process of meiosis. Because of this, a single mushroom has the ability to release a billion spores. Most basidiospores are forcibly discharged, and are thus considered ballistospores.