Habitat: In composted, mulched gardens and manured fields and at the edge of woods from late summer through fall.
Agaricus arvensis is called commonly the ‘Horse Mushroom.’ It can be quite large, has a sweet aniseed almond smell and cog-wheeled double ring. The caps will often bruise yellow if rubbed, and the flesh will sometimes turn yellowish on exposure to air - but the flesh in the base of the slightly bulbous stem is not yellow, which helps distinguish it from toxic species, like the phenolic odored Agaricus xanthodermus, the ‘Yellow Stainer’.
Another potential lookalike is the deadly Amanita bisporigera (also known as Amanita virosa). However, this amanita has a sac-liike cup at its base, lacks the ainse fragrance of Agaricus arvensis, and produces a white, rather than the brown spore print of Agaricus species. Saprotrophic. Edible.