Basidiomycota comprise the most morphologically complex group of macrofungi. They include mushrooms and toadstools, and rust and smut parasites of plants. Basidiomycetes grow as networks of hyphae colonizing nutrient substrates. Reproduction is by airborne spores produced from basidiomes such as mushrooms. Features used in identification show frequent convergent evolution – classification is changing as molecular phylogeny reveals true relationships.

Basidiomycetes are essential in carbon cycling in temperate and boreal forests, as wood decomposers and ectomycorrhizal symbionts. They form underground resource-sharing networks (the ‘wood-wide web’) which support plant biodiversity in forest ecosystems. Some form symbioses with animals, notably ants, termites, beetles and wasps. Others form lichens with photosynthetic microbes.

Economically, mushrooms are valued for food and for bioactive compounds exploited in traditional medicine. Wood decay Basidiomycetes can destroy construction timber, but are valuable in lignocellulose conversion, for composting and as potential producers of biofuels. Rusts and smuts cause major crop losses.

Key concepts

• The unique mode of growth and development in Fungi reaches its most highly diversified form in Basidiomycota: modular, indeterminately tip-extending hyphae branch and anastomose, produced a network that comprises the individual organism. The differentiation of multicellular tissues, as in mushroom development, occurs in an environmentally cued, context-responsive manner.
  
• Basidiomycota exemplify convergent evolution, particularly in the form of reproductive structure, the basidiome (mushroom). Extensive recent changes in classification result from new evidence from molecular phylogeny for true evolutionary relationships within the group.
  
• The ‘wood-wide web’ of underground resource-sharing networks in forest soils is mainly formed from the mycelium of basidiomycete fungi. Mycelium scavenges and transports plant nutrients from soil, and supports the growth of plants able to connect to it. Symbiotic and decomposing activities by fungi of the wood-wide web contribute to plant productivity and diversity, to woodland carbon cycling and to mineral nutrient dynamics.
  
• Symbiosis is an important feature of the ecology of the group. Basidiomycete fungi include biotrophics such as rust and smut parasites of plants, mutualistic symbionts including ectomycorrhiza of forest trees, lichen associations with photosynthetic microbes. Animal symbioses are common, particularly with ants, termites, beetles and wasps.
  
• Economically, their ability to degrade lignocellulose and convert inorganic nitrogen compounds to amino acids and protein, enables basidiomycetes to convert wood into food for animals. Humans exploit this in mushroom gathering and cultivation. The wood rotting ability of basidiomycetes is exploited in waste composting, and potentially for biofuel production from woody waste.
  
• Basidiomycetes produce a very large array of bioactive metabolites. Some of these confer extreme toxicity on fungi such as Amanita phalloides, the death cap. Others are pharmacologically valuable, and are exploited mainly in traditional medicine.
  
• Economic losses due to basidiomycetes include millions of pounds worth of damage to construction timber per annum, and crop losses due to rust and smut fungi. The emergent human pathogen Cryptococcus is a basidiomycete.