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The Agaricomycetes contains approximately 16,000 described species, which is 98% of the described species in the Agaricomycotina (Kirk et al. 2001). Agaricomycetes produce mushrooms, and are therefore the most familiar and conspicuous of all Fungi. Other Fungi produce macroscopic fruiting bodies as well, but the diversity of forms in the Agaricomycetes is unmatched.
Fruiting bodies of Agaricomycetes range from millimeter-scale cyphelloid forms, which look like tiny cups, to the giant polypores Rigidoporus ulmarius (up to 316 kg; see the Fungi page) and Bridgeoporus nobilissimus (up to 130 kg; Burdsall et al. 1996). Agaricomycetes include not only the largest fruiting bodies in Fungi, but perhaps the largest and oldest individuals in any group of organisms. Clones of the honey mushroom, Armillaria gallica, produce average-sized mushrooms, but their mycelial networks have been estimated to cover areas up to 15 hectares, with a mass of 10,000 kg (comparable to a blue whale), and an age of 1500 years (Smith et al. 1992).
Agaricomycetes function as decayers, pathogens, parasites, and mutualistic symbionts of both plants and animals. They make their broadest ecological impacts through their activities as wood-decayers and ectomycorrhizal symbionts of forest trees (such as pines, oaks, dipterocarps, and eucalypts; Rayner and Boddy 1988; Smith and Read 1997). Agaricomycetes are widespread in virtually all terrestrial ecosystems, and a few have secondarily returned to aquatic habitats.
The majority of edible mushrooms are Agaricomycetes (truffles and morels are in the Ascomycota, however). Cultivated edible Agaricomycetes are decayers that have been domesticated, such as button mushrooms (Agaricus bisporus), shiitake (Lentinula edodes), oyster mushrooms (Pleurotus ostreatus), and others. Most of the wild-collected edible species are mycorrhizal (making them difficult or impossible to cultivate), such as porcini (Boletus edulis), chanterelles (Cantharellus cibarius), and matsutake (Tricholoma matsutake). Would-be mushroom hunters should be aware that some species of Agaricomycetes produce secondary metabolites that render them toxic or hallucinogenic (or bioluminescent; Fig. 1).
Mushrooms have been used for medicinal and spiritual purposes in diverse human societies. For example, the 5300-year-old Ice Man who was discovered in a Tyrolean glacier was found carrying pieces of the birch polypore, Piptoporus betulinus, which he may have been using to treat intestinal parasites (Capasso 1998). Another fascinating item of ethnomycology comes from the Pacific Northwest of the United States, where Indigenous People have carved figurines out of the fruiting bodies of the polypore Fomitopsis officinalis to serve as guardians at the graves of shamans (Fig. 1; Blanchette et al. 1992).
Figure 1. Magic mushrooms. Left: The bioluminescent Agaricomycete, Panellus stypticus (Agaricales), photographed by its own light. © D. Hibbett. Right: Grave guardian carved from a fruiting body of Fomitopsis officinalis (Polyporales). © Mycological Society of America. From Blanchette et al. (1992); used with permission.