Agaricus bisporus

The pileus or cap of the original wild species is a pale grey-brown, with broad, flat scales on a paler background and fading toward the margins. It is first hemispherical before flattening out with maturity, and 5–10 centimetres (2–4 inches) in diameter. The narrow, crowded gills are free and initially pink, then red-brown, and finally a dark brown with a whitish edge from the cheilocystidia. The cylindrical stipe is up to 6 cm (2+1⁄2 in) tall by 1–2 cm (1⁄2–3⁄4 in) wide and bears a thick and narrow ring, which may be streaked on the upper side. The firm flesh is white, although it stains a pale pinkish-red on bruising.[2][3] The spore print is dark brown. The spores are oval to round and measure approximately 4.5–5.5 μm × 5–7.5 μm, and the basidia usually two-spored, although two-tetrasporic varieties have been described from the Mojave Desert and the Mediterranean, with predominantly heterothallic and homothallic lifestyles, respectively.[4][5]

The common mushroom has a complicated taxonomic history. It was first described by English botanist Mordecai Cubitt Cooke in his 1871 Handbook of British Fungi, as a variety (var. hortensis) of Agaricus campestris.[6][7] Danish mycologist Jakob Emanuel Lange later reviewed a cultivar specimen, and dubbed it Psalliota hortensis var. bispora in 1926.[8] In 1938, it was promoted to species status and renamed Psalliota bispora.[9] Emil Imbach (1897–1970) imparted the current scientific name of the species, Agaricus bisporus after the genus Psalliota was renamed to Agaricus in 1946.[10] The specific epithet bispora distinguishes the two-spored basidia from four-spored varieties.

This mushroom is commonly found worldwide in fields and grassy areas following rain, from late spring to autumn, especially in association with manure.

Mushroom and truffle production – 2019
Country	Millions of tonnes
China	8.94
Japan	0.47
United States	0.38
Poland	0.36
Netherlands	0.30
World	11.90
Source: FAOSTAT of the United Nations[17]

The earliest scientific description of the commercial cultivation of A. bisporus was made by French botanist Joseph Pitton de Tournefort in 1707.[18] French agriculturist Olivier de Serres noted that transplanting mushroom mycelia would lead to the propagation of more mushrooms.

Originally, cultivation was unreliable as mushroom growers would watch for good flushes of mushrooms in fields before digging up the mycelium and replanting them in beds of composted manure or inoculating 'bricks' of compressed litter, loam, and manure. Spawn collected this way contained pathogens, and crops would be infected or not grow.[19] In 1893, sterilized, or pure culture, spawn was discovered and produced by the Pasteur Institute in Paris for cultivation on composted horse manure.[20]

Modern commercial varieties of the common agaricus mushroom were originally light brown. The white mushroom was discovered in 1925 growing among a bed of brown mushrooms at the Keystone Mushroom Farm in Coatesville, Pennsylvania. Louis Ferdinand Lambert, the farm's owner and a mycologist by training, brought the white mushroom back to his laboratory. As with the reception of white bread, it was seen as a more attractive food item and became grown and distributed.[21] Similar to the commercial development history of the navel orange and Red Delicious apple, cultures were grown from the mutant individuals. Most cream-colored store mushrooms marketed today are products of this 1925 chance natural mutation.

A. bisporus is now cultivated in at least seventy countries worldwide.[10]

In the U.S., the white button form of A. bisporus alone accounts for about 90% of mushrooms sold.[11]

In a 100-gram serving, raw white mushrooms provide 93 kilojoules (22 kilocalories) of food energy and are an excellent source (> 19% of the Daily Value, DV) of the B vitamins, riboflavin, niacin, and pantothenic acid (table). Fresh mushrooms are also a good source (10–19% DV) of the dietary mineral phosphorus (table).

While fresh A. bisporus only contains 0.2 micrograms (8 IU) of vitamin D per 100 g, the ergocalciferol (D₂) content increases substantially to 11.2 micrograms (446 IU)[22] after exposure to UV light.[23][24]

•  Fungi portal
• List of Agaricus species

• Benjamin, Denis R. (1995). Mushrooms: poisons and panaceas—a handbook for naturalists, mycologists and physicians. New York: WH Freeman and Company. ISBN 0-7167-2600-9.