Basidium

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Schematic showing a basidiomycete mushroom, gill structure, and spore-bearing basidia on the gill margins.

The basidium (pl., basidia) is a microscopic structure found on the hymenophore of fruiting bodies of basidiomycete fungi. As such, the presence of basidia is one of the main characteristic features of the Basidiomycota. The basidium usually bears four sexual spores called basidiospores; occasionally the number may be two or even eight. An immature basidium is known as a basidiole.

The word basidium literally means little pedestal, from the way in which the basidium supports the spores. However, some biologists suggest that the structure more closely resembles a club.

[edit] Formation of the basidia

A basidium is generally a single cell (a holobasidium), but in some cases there is a secondary development into a two-celled or four-celled structure (a phragmobasidium). For instance the Uredinales (rusts) have four-celled phragmobasidia. Sometimes the basidium (metabasidium) develops from a probasidium, which is a specialized cell which is not elongated like a typical hypha.