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Agaricus arvensis   (Horse Mushroom)
North America, Europe
Cap 8-20 cm diameter, stem 8-10 cm tall * 2-3 cm diameter

Agaricus arvensis, commonly known as the horse mushroom, is a sometimes massive agaric that has a white cap, ringed stem, and pink or chocolate coloured gills. It grows on soil (often heavily fertilized) or on vegetable debris.

Cap white or cream-coloured, may have fine scales, first hemispherical in shape before flattening out with maturity. The flesh is white, firm and thick. Gills are at first white, becoming pink, then chocolate brown or blackish, free and crowded. Stem is white or cream, slightly club-shaped and smooth or finely scaly below the ring. The ring is white or cream, pendulous and superior. Viewed from below, on a closed-cap specimen, it has a well-developed 'cogwheel' pattern around the stem.

Similar species include Agaricus macrosporus which is very fleshy, with scaly stem girdles and Agaricus sylvicola which is a woodland variety. Agaricus augustus and the poisonous Agaricus xanthoderma are also similar. Be careful not to confuse it with deadly poisonous Amanita species, which has white gills.

Agaricus arvensis on the web site.

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