Agaricus campestris is a widely eaten gilled mushroom closely related to the cultivated button mushroom Agaricus bisporus. It is commonly known as the field mushroom or, in North America, meadow mushroom. The cap is white, may have fine scales, and is 3 to 12 centimetres (1+1⁄8 to 4+3⁄4 in) in diameter; it is first hemispherical in shape before flattening out with maturity. The gills are initially pink, then red-brown and finally a dark brown, as is the spore print. The stipe is 3 to 10 cm (1+1⁄8 to 3+7⁄8 in) tall, 1–2 cm wide, predominantly white and bears a single thin ring. The taste is mild. The white flesh bruises a dingy reddish brown, as opposed to yellow in the poisonous Agaricus xanthodermus and similar species. The thick-walled, dark brown, elliptical spores measure 5.5–8 μm by 4–5 μm. Cheilocystidia are absent. (Source: Wikipedia.org, CC BY-SA)