Agaricus bisporus is the most widely cultivated mushroom, grown in more than 70 countries and sold as white button, cremini and portobello. Its basidia usually bear two spores, which gives the species its name. Wild forms have a pale grey-brown cap with broad, flat scales; most cream-coloured commercial strains derive from a white mutant found in Pennsylvania in 1925. It is native to grasslands of Eurasia and North America.
Edible; the world's most widely eaten mushroom. It contains agaritine, an experimental carcinogen at high laboratory doses; cooking cuts it by up to 90%, and evidence is inadequate to call dietary amounts carcinogenic. Wild collectors must rule out destroying angels (white gills, volva), the yellow stainer A. xanthodermus (phenol odor, yellow bruising; causes vomiting) and Entoloma sinuatum (yellowish gills turning pink, no ring).
Never eat a wild mushroom based on a web page — confirm with an expert.
Mycology is an evolving science: names, classifications and safety information change as research advances. Entries are compiled from cited sources and reviewed, but may be incomplete or out of date — check the sources, and never rely on this library alone to identify or eat a mushroom.
Habitat
Saprotrophic in rich soil, compost, manure and grassland, also with cypress; wild fruiting mainly from autumn to winter. Cultivated indoors year-round on pasteurized compost.
Distribution
Native to grasslands of Eurasia and North America; widespread worldwide and cultivated in more than 70 countries. A four-spored, predominantly heterothallic variety is known from the Sonoran Desert of California, and a four-spored, homothallic wild population from the Mediterranean.
Characteristics
Cap: Wild caps typically 5–10 cm, hemispherical then flattening; pale grey-brown with broad, flat scales on a paler ground (white in many cultivated strains); mature commercial 'portobello' caps 10–15 cm and brown. Gills: Free, narrow, crowded; pink at first, then red-brown, then dark brown with a whitish edge. Stem: Cylindrical, up to 6 cm tall and 1–2 cm thick. Ring: Thick and narrow, may be streaked above. Flesh: Firm, white; bruising pale pinkish-red. Spore print: Dark brown; spores oval to round, about 4.5–5.5 × 5–7.5 µm; basidia usually 2-spored.
