Agaricus arvensis
Agaricus arvensis, commonly known as the horse mushroom, is a mushroom-forming fungus of the genus Agaricus.
Taxonomy
It was described as Agaricus arvensis by Jacob Christian Schaeffer in 1774, and given numerous binomial descriptions since. Its specific epithet arvensis means "of the field".Description
The cap is across, whitish, smooth, and dry; it stains yellow, particularly when young. The gills are pale pink to white at first, later passing through grey and brown to become dull chocolate. A large, spreading ring has white above, but sometimes with yellowish scales underneath. Viewed from below, on a closed-cap specimen, the twin-layered ring has a well-developed "cogwheel" pattern around the stipe. This is the lower part of the double ring. The stalk is long and 1–3 cm wide.The spores are brown and smooth, producing a dark brown spore print. Its odor is similar to that of almond extract or marzipan, due to the presence of benzaldehyde. It tends to stain yellow on bruising.
Similar species
In addition to its similarity to other related species, this fungus can be confused with deadly species of Amanita.Agaricus osecanus is rare and lacks the almond smell. Agaricus xanthodermus, the yellow stainer, can cause stomach upsets.
Distribution and habitat
It is one of the largest white Agaricus species in Britain, West Asia, and North America.Frequently found near stables, as well as in meadows, it may form fairy rings. The mushroom is often found growing with nettles. It is associated with cypress on the North American West Coast and spruce to the east.