Agaricus xanthodermus

Cap	Initially globose but with a flat top, the cap expands to become broadly convex without an in-rolled margin. Initially pure white and matt, later greying, caps grow to between 5 and 15 cm at maturity, and they quickly turn crome yellow when scratched or bruised.
Gills	In this picture the partial veil is just beginning to rupture, revealing free, off-white gills that soon turn pink and later become grey-brown as the fruit body reaches maturity.
Stipe	The stipe diameter is 1 to 2 cm with a smooth, silky surface and a bulbous base. A large white stem ring persists through to maturity. When cut the stem flesh quickly turns from white to chrome yellow, most markedly at the stem base.
Spore print	Very dark brown.
Odour/taste	Taste not distinctive. Noticeable odour of ink, phenol or iodine, especially when the flesh is bruised or cut.
Habitat	Most commonly under hedgerows and at the edges of gardens and other areas of disturbed soil.
Season	June to October.
Occurrence	Frequent.
Similar species	Agaricus arvensis is superficially very similar but bruises more slowly and only slightly yellow; its flesh smells of aniseed rather than of iodine. Agaricus campestris is similar in appearance but does not turn yellow when cut or bruised.