What You Should Know
Agaricus xanthodermus is a common fungus that is fairly common in North America, usually found in grasslands in urban environments and forests (especially on the west coast).
However, there are dozens of species of Agaricus that exhibit yellow spots, so other characteristics must match. Some authors emphasize a strong phenolic odor, best detected by crushing the base of the stem.
This mushroom can cause severe stomach upset and should not be consumed. It may be confused with other members of the Agaricaceae family.
Other names: Yellow Stainer, Agaric jaunissant, Psalliote jaunissante (French), Prataiolo – Falso prataiolo (Italian), Karbolchampignon (German), Pieczarka karbolowa (Polish).
Agaricus xanthodermus Mushroom Identification
Saprobic; growing scattered or in large groups, sometimes clustered together or in arcs; usually appearing in grassy, cultivated areas, but occasionally found in thin woods (especially on the West Coast); summer and fall, or overwinter in warm climates; probably widely distributed in North America.
6–15 cm; round to irregularly convex when young, expanding to broadly convex or nearly flat; dry; bald, or with scattered fibrils; thin-fleshed; whitish, or brownish to pale brown, especially towards the center; usually bruising yellow when rubbed, especially near the margin—the bruised areas then changing to brownish after some time has elapsed; the margin inrolled when young.
Free from the stem; crowded; short-gills frequent; whitish at first, then pinkish, and finally dark brown; when in the button stage, covered with a membranous white or yellowed partial veil.
4–15 cm long; 1–3 cm thick; more or less equal above a slightly enlarged base; bald; whitish, bruising yellow (then brownish); sometimes brownish overall in age; with a large, flaring, thick, yellow-staining ring that has a thick outer edge.
White; sometimes yellowing when sliced; bright yellow in the base of the stem.
Odor and Taste
Odor reported as phenolic, but sometimes faint; crush the flesh in the stem base to be sure.
Dull brown overall; cap notably thin-fleshed and fragile.
Agaricus xanthodermus Look-Alikes
Superficially very similar but only slightly yellowish. Its flesh smells more like fennel than iodine or phenol.
Similar in appearance but does not turn yellow when cut or crushed.
Agaricus xanthodermus Taxonomy and Etymology
In 1876 French botanist Léon Gaston Genevier (1830–1880) described this species and give the naming Agaricus xanthodermus.
The specific epithet xanthodermus represents a Greek word and means "yellow-skinned".
Agaricus xanthodermus Toxicity
Agaricus xanthodermus is one of the most commonly ingested poisonous mushrooms (Hender et al., 2000). If eaten, symptoms may include abdominal cramps, nausea, vomiting and diarrhea. Less common symptoms include headache, dizziness, sweating and drowsiness. It should be noted that some people have eaten this species without apparent ill effects.
Also, A. xanthodermus contains a molecule, 4,4′-dihydroxy-azobenzene, that in high doses, is carcinogenic to mice. At lower concentrations, however, the azo compound does not have tumor-inducing effects (Toth et al., 1989).
Although other edible Agaricus species, such as A. augustus, A. arvensisand A. silvicola, turn yellow to a greater or lesser extent, they do not display such an intense reaction as A. xanthodermus. This species is commonly found in grass under trees or in parks, but seldom in deep forest (Kerrigan et al., 2005). It is found in North America, Europe, and Africa.
Agaricus xanthodermus Synonyms
Agaricus xanthodermus Genev., 1876
Pratella xanthoderma (Genev.) Gillet, 1884
Psalliota xanthoderma (Genev.) Richon & Roze, 1885
Fungus xanthoderma (Genev.) Kuntze, 1898
Psalliota flavescens Richon & Roze, 1888
Agaricus jodoformicus Speg., 1898
Agaricus xanthodermus var. lepiotoides Maire
Psalliota xanthoderma var. lepiotoides (Maire) Rea
Psalliota xanthoderma var. grisea A. Pearson
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