Agaricus Xanthodermus: The Ultimate Mushroom Guide
About The Agaricus Xanthodermus Mushroom
Agaricus Xanthodermus is a widespread mushroom and fairly common in North America, usually appearing in grassy areas in urban settings, but also known from thin woods (especially on the West Coast).
There are dozens of Agaricus species that bruise yellow, however, so other features will need to match. Some authors stress the strong phenolic odor, best detected by crushing the base of the stem.
Agaricus Xanthodermus can cause serious stomach upsets and so should not be eaten. It can be confused with other members of the Agaricaceae.
Other names: Yellow Stainer, Agaric jaunissant, Psalliote jaunissante (French), Prataiolo – Falso prataiolo (Italian), Karbolchampignon (German), Pieczarka karbolowa (Polish).
Agaricus Xanthodermus 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
Is superficially very similar to Agaricus Xanthodermus but it bruises more slowly and only slightly yellow; its flesh smells of aniseed rather than of iodine or phenol.
Is similar in appearance but does not turn yellow when cut or bruised.
Agaricus Xanthodermus Taxonomy & Etymology
The official description and naming of Agaricus Xanthodermus, in 1876, was made by the French botanist Léon Gaston Genevier (1830–1880), who is mainly remembered for his pioneering work on the plant genus Rubus, which contains the various species and varieties of Blackberry, Raspberry, Mulberry, Dewberry, etc and their plethora of hybrids.
Synonyms of Agaricus xanthodermus include Psalliota flavescens Richon & Roze, Psalliota xanthoderma (Genev.) Richon & Roze, Agaricus xanthodermus var. lepiotoides Maire, Psalliota xanthoderma var. lepiotoides (Maire) Rea, Psalliota xanthoderma var. grisea A. Pearson, and Agaricus xanthodermus var. griseus (A. Pearson) Bon & Cappelli.
The specific epithet xanthodermus comes from the Greek for 'yellow-skinned', and this species is the most infamous of some mildly toxic Agaricus species whose stem flesh turns yellow when cut. The Yellow Stainer, however, is particularly dangerous because it looks so much like an edible Agaricus such as the Field Mushroom, Agaricus campestris or the Horse Mushroom, Agaricus arvensis. As a result, it is one of the most commonly consumed poisonous mushrooms.
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.
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