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In fungi, a basidiocarp, basidiome, or basidioma ( pl. basidiomata) is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do not produce such structures. As with other sporocarps, epigeous (above-ground) basidiocarps that are visible to the naked eye (especially those with a more or less agaricoid morphology) are commonly referred to as mushrooms, while hypogeous (underground) basidiocarps are usually called false truffles.
All basidiocarps serve as the structure on which the hymenium is produced. Basidia are found on the surface of the hymenium, and the basidia ultimately produce spores. In its simplest form, a basidiocarp consists of an undifferentiated fruiting structure with a hymenium on the surface; such a structure is characteristic of many simple jelly and club fungi. In more complex basidiocarps, there is differentiation into a stipe, a pileus, and/or various types of hymenophores.
Basidiocarps of Amanita muscaria, an agaric.
Basidiocarps of Craterellus tubaeformis, a cantharelloid fungus.
Basidiocarps are classified into various types of growth forms based on the degree of differentiation into a stipe, pileus, and hymenophore, as well as the type of hymenophore, if present.
Growth forms include:
Basic divisions of Agaricomycotina were formerly based entirely upon the growth form of the mushroom. Molecular phylogenetic investigation (as well as supporting evidence from micromorphology and chemotaxonomy) has since demonstrated that similar types of basidiomycete growth form are often examples of convergent evolution and do not always reflect a close relationship between different groups of fungi. For example, agarics have arisen independently in the Agaricales, the Boletales, the Russulales, and other groups, while secotioid fungi and false truffles have arisen independently many times just within the Agaricales.