Common field mushroom. Agaricus campestris is commonly known as the field mushroom or, in North America, meadow mushroom. It is a widely eaten gilled mushroom, A fungus is any member of a large group of eukaryotic organisms that includes microorganisms such as yeast and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, protists, and bacteria. They have long been used as a source of food, as a leavening agent for bread, and in fermentation of various food products, such as wine, beer, and soy sauce. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi are used industrially and in detergents. The fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Little is known of the true biodiversity of Kingdom Fungi, which has been estimated at 1.5 million to 5 million species, with about 5% of these having been formally classified. Undated, no illustrator credited.