The conspicuous umbrella-shaped fruiting body (sporophore) of certain fungi, typically of the order Agaricales in the phylum Basidiomycota but also of some other groups. Popularly, the term mushroom is used to identify the edible sporophores; the term toadstool is often reserved for inedible or poisonous sporophores. There is, however, no scientific distinction between the two names, and either can be properly applied to any fleshy fungus fruiting structure. In a very restricted sense, mushroom indicates the common edible fungus of fields and meadows (Agaricus campestris). A very closely related species, A. bisporus, is the mushroom grown commercially and seen in markets.
Umbrella-shaped sporophores are found chiefly in the agaric family (Agaricaceae), members of which bear thin, bladelike gills on the undersurface of the cap from which the spores are shed. The sporophore of an agaric consists of a cap (pileus) and a stalk (stipe). The sporophore emerges from an extensive underground network of threadlike strands (mycelium). An example of an agaric is the honey mushroom (Armillaria mellea). Mushroom mycelia may live hundreds of years or die in a few months, depending on the available food supply. As long as nourishment is available and temperature and moisture are suitable, a mycelium will produce a new crop of sporophores each year during its fruiting season.
Fruiting bodies of some mushrooms occur in arcs or rings called fairy rings. The mycelium starts from a spore falling in a favourable spot and producing strands (hyphae) that grow out in all directions, eventually forming a circular mat of underground hyphal threads. Fruiting bodies, produced near the edge of this mat, may widen the ring for hundreds of years.