Agaricus xanthodermus

Description

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.

Common names: Yellow Stainer, Agaric jaunissant, Psalliote jaunissante (French), Prataiolo – Falso prataiolo (Italian), Karbolchampignon (German), Pieczarka karbolowa (Polish).

Mushroom Identification

1. Ecology

   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.

2. Cap

   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.

3. Gills

   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. Stem

   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.

5. Flesh

   White; sometimes yellowing when sliced; bright yellow in the base of the stem.

6. Odor and Taste

   Odor reported as phenolic, but sometimes faint; crush the flesh in the stem base to be sure.

7. Dried Specimens

   Dull brown overall; cap notably thin-fleshed and fragile.

8. Spore Print

   Dark brown.

Look-Alikes

1. Agaricus arvensis

   Superficially very similar but only slightly yellowish. Its flesh smells more like fennel than iodine or phenol.

2. Agaricus campestris

   Similar in appearance but does not turn yellow when cut or crushed.

History

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".

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.

Synonyms

1. Agaricus xanthodermus Genev., 1876

2. Pratella xanthoderma (Genev.) Gillet, 1884

3. Psalliota xanthoderma (Genev.) Richon & Roze, 1885

4. Fungus xanthoderma (Genev.) Kuntze, 1898

5. Psalliota flavescens Richon & Roze, 1888

6. Agaricus jodoformicus Speg., 1898

7. Agaricus xanthodermus var. lepiotoides Maire

8. Psalliota xanthoderma var. lepiotoides (Maire) Rea

9. Psalliota xanthoderma var. grisea A. Pearson

Photo sources:

Photo 1 - Author: Ron Pastorino (Ronpast) (CC BY-SA 3.0)

Photo 2 - Author: Velella (CC BY-SA 3.0)

Photo 3 - Author: Strobilomyces (CC BY-SA 3.0)

Photo 4 - Author: Tomasz Sobczak (CC BY-SA 4.0)

Photo 5 - Author: Fernando Losada Rodríguez (CC BY-SA 4.0)