Time Lapse of Mushrooms Growing. A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. Like all fungi, mushrooms are not plants and do not undergo photosynthesis. The standard for the name mushroom is the cultivated white button mushroom, Agaricus bisporus; hence the word mushroom is most often applied to those fungi (Basidiomycota, Agaricomycetes) that have a stem (stipe), a cap (pileus), and gills (lamellae, sing. lamella) or pores on the underside of the cap. Mushroom describes a variety of gilled fungi, with or without stems, and the term is used even more generally, to describe both the fleshy fruiting bodies of some Ascomycota and the woody or leathery fruiting bodies of some Basidiomycota, depending upon the context of the word. Forms deviating from the standard morphology usually have more specific names, such as puffball, stinkhorn, and morel, and gilled mushrooms themselves are often called agarics in reference to their similarity to Agaricus or their place Agaricales. By extension, the term mushroom can also designate the entire fungus when in culture; the thallus (called a mycelium) of species forming the fruiting bodies called mushrooms; or the species itself.