Pleurotus ostreatus, the pearl oyster and blue oyster mushroom or tree oyster mushroom, is a common edible mushroom.
A mushroom, or toadstool, is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source.
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) on the underside of the cap.
Mushroom" also describes a variety of other gilled fungi, with or without stems, therefore the term is used to describe the fleshy fruiting bodies of some Ascomycota.
Mushrooms are a rich source of nutrients which include a rich supply of B vitamins like riboflavin, folate, thiamine, pantothenic acid, and niacin.