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mushroom, type of basidium fungus characterized by spore-bearing gills on the underside of the umbrella- or cone-shaped cap. The name toadstool is popularly reserved for inedible or poisonous mushrooms, but this classification has no scientific basis. The only safe way of distinguishing between the edible and the poisonous species is to learn to identify them. Some poisonous mushrooms are of the genus Amanita. The genus includes the fly agaric, Amanita muscaria, and the death angel or destroying angel, A. virosa.
The use of edible mushrooms for food dates back at least to early Roman times. Originally a delicacy for the elite, mushrooms are now extensively grown on a commercial scale, especially the cultivated mushroom or champignon, Agaricus bisporus, and the shiitake mushroom, Lentinus edodes. Their culture requires careful control of temperature and humidity. The bulk of the crop in the United States is grown near Philadelphia. In Europe more than 50 species of mushrooms are marketed. Although mushrooms contain some protein and minerals, they are largely composed of water and hence are of limited nutritive value.
The truffle, puffball, and other edible fungi are sometimes also called mushrooms. In all cases the term mushroom is properly restricted to the above-ground portion, which is the reproductive organ. Mushrooms are classified in the kingdom Fungi, phylum (division) Basidiomycota.
See A. H. Smith and N. A. Weber, The Mushroom Hunter's Field Guide (rev. ed. 1980); O. K. Miller, Jr., Mushrooms of North America (rev. ed. 1979); G. H. Lincoff, The Audubon Society Field Guide to North American Mushrooms (1981).
A macroscopic fungus with a fruiting body (also known as a sporocarp). Approximately 14% (10,000) described species of fungi are considered mushrooms. Mushrooms grow aboveground or underground. They have a fleshy or nonfleshy texture. Many are edible, and only a small percentage are poisonous.
Mushrooms reproduce via microscopic spheres (spores) that are roughly comparable to the seeds of higher plants. Spores are produced in large numbers on specialized structures in or on the fruiting body. Spores that land on a suitable medium absorb moisture, germinate, and produce hyphae that grow and absorb nutrients from the substratum. If suitable mating types are present and the mycelium (the threadlike filaments or hyphae that become interwoven) develops sufficiently to allow fruiting, the life cycle will continue. In nature, completion of the life cycle is dependent on many factors, including temperature, moisture and nutritional status of the substratum, and gas exchange capacity of the medium.
Fewer than 20 species of edible mushrooms are cultivated commercially. The most common cultivated mushroom is Agaricus bisporus, followed by the oyster mushroom (Pleurotus spp.). China is the leading mushroom-producing country; Japan leads the world in number of edible species cultivated commercially.
Mushrooms may be cultivated on a wide variety of substrates. They are grown from mycelium propagated on a base of steam-sterilized cereal grain. This grain and mycelium mixture is called spawn, which is used to seed mushroom substrata.
Mushrooms contain digestible crude protein, all essential amino acids, vitamins (especially provitamin D-2), and minerals; they are high in potassium and low in sodium, saturated fats, and calories. Although they cannot totally replace meat and other high-protein food in the diet, they can be considered an important dietary supplement and a health food.
Fungi have been used for their medicinal properties for over 2000 years. Although there remains an element of folklore in the use of mushrooms in health and medicine, several important drugs have been isolated from mushroom fruiting bodies and mycelium. The best-known drugs obtained are lentinan from L. edodes, grifolin from Grifola frondosa, and krestin from Coriolus versicolor. These compounds are protein-bound polysaccharides or long chains of glucose, found in the cell walls, and function as antitumor immunomodulatory drugs. See Fungi, Medical mycology