Agaricus arvensis is a saprobic fungus that grows in fields and grassy areas. It is a large, edible mushroom with a cap that can reach up to 15 cm (6 inches) in diameter. The cap is initially hemispherical, then expands and flattens with age. The gills are initially pink, then turn brown and finally black as the mushroom matures. The stem is white and can be up to 10 cm (4 inches) tall.