The Division Basidiomycota is a large taxon within the Kingdom Fungi that includes those species that produce spores in a club_shaped structure called a basidium. Essentially the sister group of the Ascomycota, it contains some 30,000 species (37% of the described fungi). The Basidiomycota was traditionally divided into Homobasidiomycetes — the true mushrooms — and Heterobasidiomycetes — the rusts and smuts. The Basidiomycota is now thought to comprise three major clades: the Hymenomycotina (Hymenomycetes; mushrooms), the Ustilaginomycotina (Ustilaginomycetes; true smut fungi), and the Teliomycotina (Urediniomycetes; rusts).

Basidiomycota include both unicellular (some yeasts) and multicellular forms and sexual and asexual species. They occur in terrestrial and aquatic environments (including the marine environment) and can be characterized by bearing sexual spores on basidia, having a long-lived dikaryon, and usually showing clamp connections.

Basidium

The basidium (pl., basidia) is a microscopic structure found at the ends of hyphae in the fruiting bodies of basidiomycete fungi — that is, the basidium is the diagnostic feature of those fungi classified as Basidiomycota. The basidium usually bears four sexual spores called basidiospores. 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; thus, the Basidiomycota are also known as the club fungi.

Life cycle

Basidiomycetes have a peculiar sexuality. They most often are heterothallic, but with a bipolar (unifactorial) or tetrapolar (bifactorial) mating system acting like many sexes. Usually, somatogamy (hyphogamy) is performed.

Most basidiomycetes live out most of their life as dikaryotic (heterokaryotic) mycelium, with karyogamy and meiosis happening in the basidium. There are examples of diploid life cycles as well: the genus Xerula was found to sometimes produce diploid clones as spores, and Armillaria, a common forest pathogen, has diploid mycelium, where karyogamy directly follows plasmogamy.

Asexual spores (conidia) are more and more being discovered also in the basidiomycetes.

References and External Links

• Basidiomycota (http://tolweb.org/tree?group=Basidiomycota&contgroup=Fungi) at the Tree of Life Web Project