A yellow-staining eastern North American Agaricus (section Xanthodermatei) with a flattened, brownish-gray cap whose fibers break up into scales on a paler background. The stem base turns yellow when cut, and the mushroom often smells of phenol. It causes gastrointestinal upset in many people.
Poisonous: contains gastrointestinal irritants (phenolic compounds typical of section Xanthodermatei) that cause vomiting and diarrhea in many people, although some people are not affected. Do not eat. Bright yellow staining in the cut flesh of the stem base separates it from edible woodland Agaricus species. The phenolic odor is not always noticeable, so do not rely on smell alone.
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Habitat
Saprobic, scattered or in groups under hardwoods or conifers, in woods and under planted trees in lawns and other urban settings; mainly summer and fall.
Distribution
North America, mainly east of the Rocky Mountains and northern in distribution; probably widespread in the east (MushroomExpert.com collections from Minnesota and Illinois). Eurasian populations once recorded under this name are now called A. moelleri. Similar species elsewhere include A. pocillator and A. leptocaulis in the southeastern United States and A. deardorffensis and A. buckmacadooi in the west.
Characteristics
Cap: 6-14 cm, convex to nearly flat; dry; brownish gray with a darker center, the cover breaking into scales and streaks over a whitish ground; yellows when rubbed, especially at the margin; KOH yellow. Gills: free, crowded, whitish at first, then pink, then brown; young gills covered by a rubbery partial veil that stains yellow, then brown. Stem: 7-11 cm long, 1-2.5 cm thick, equal or slightly enlarged at the base but without an abrupt bulb; persistent whitish ring; bruises yellow, then slowly brown. Flesh: white, turning bright yellow in the stem base when cut. Odor: phenolic or not distinctive, strongest at the stem base. Spore print: brown. Spores: 5-6 x 3.5-4.5 µm, ellipsoid, smooth (MushroomExpert.com).
