Agaricus xanthodermus, commonly known as the Yellow Stainer, is a medium to large agaric with a pale cream to white cap that often stains yellow when bruised, greyish-pink to dark brown gills, and a thick stem with a prominent ring. It grows singly or in groups on soil, often in grassy areas, gardens, parks, and roadside verges, typically appearing from late summer to autumn.

Cap at first white and develops minute greyish scales as it ages. When bruised, it stains yellowish. It begins sub-spherical in shape, becoming broadly convex and eventually flattening. The flesh is white, does not change colour, and is thick and firm. Gills are free from the stem and crowded, with frequent short gills. They are whitish at first, turning pinkish and eventually dark brown. In the button stage, they are covered by a membranous partial veil that is white or sometimes yellowed. Stem more or less equal in width above a slightly enlarged base. It is bald and whitish, bruising yellow and sometimes becoming brownish with age. A large, flaring, thick ring is present, which stains yellow and has a prominent outer edge. Spore print very dark brown.

Microscopic Features: The spores are ellipsoidal or ovoid, smooth, and measure 4.5–6.5 by 3.5–5.5 µm.

Agaricus xanthodermus on the www.first-nature.com web site.
Agaricus xanthodermus on the MushroomExpert.Com Web site.

The second photo is by Huafang and licensed under the Attribution-ShareAlike 3.0 Unported license.