Agaricus bisporus

Agaricus bisporus is an edible basidiomycete mushroom native to grasslands in Eurasia and North America. It has two color states while immature – white and brown – both of which have various names, with additional names for the mature state. A. bisporus is cultivated in more than 70 countries and is one of the most commonly and widely consumed mushrooms in the world. 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 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 tall by 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. 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. This mushroom is commonly found worldwide in fields and grassy areas following rain, from late spring to autumn, especially in association with manure. It is widely collected and eaten in many parts of the world; however, it resembles deadly or poisonous lookalikes (see below). The common mushroom could be confused with young specimens of a group of lethal mushrooms in the Amanita genus referred to as destroying angels, but the latter may be distinguished by their volva or cup at the base of the mushroom and pure white gills (as opposed to pinkish or brown of A. bisporus). A more common and less dangerous mistake is to confuse A. bisporus with Agaricus xanthodermus, an inedible mushroom found worldwide in grassy areas. A. xanthodermus has an odor reminiscent of phenol; its flesh turns yellow when bruised.