basidium

A basidium is a specialized, typically club-shaped cell found in the Basidiomycota, one of the main fungal phyla. It is the site where sexual reproduction takes place, including karyogamy and meiosis, leading to the production of haploid basidiospores. Basidia form on the hymenial surfaces of fruiting bodies called basidiocarps, such as mushrooms, bracket fungi, and puffballs.

During sexual development, compatible hyphae fuse in a process called plasmogamy, resulting in a dikaryotic state within the developing basidium. The nuclei then fuse (karyogamy) to form a diploid nucleus, which immediately undergoes meiosis to generate haploid spores. Each basidium typically bears spores at the tips of slender projections called sterigmata, though the exact number of spores can vary among species.

Most basidia produce four basidiospores, which are forcibly discharged and dispersed to germinate into new fungal hyphae. Some basidia may be two- or eight-spored, reflecting variation among different basidiomycete groups. The morphology and arrangement of basidia, together with other microscopic features, are important in the taxonomy and identification of Basidiomycota.

In summary, the basidium is the reproductive cell where meiosis occurs and spores are formed in basidiomycete fungi, playing a central role in their life cycle and in the diversity of this fungal lineage.