E-Flora BC: Electronic Atlas of the Flora of British Columbia

Agaricus xanthoderma Genev.
yellow-staining Agaricus (yellow-stainer)

Species account author: Ian Gibson.
Extracted from Matchmaker: Mushrooms of the Pacific Northwest.

Introduction to the Macrofungi

© Alex Bodden  Email the photographer   (Photo ID #71558)

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Distribution of Agaricus xanthoderma
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Species Information

Agaricus xanthodermus' is a commonly used name, but if the name means 'yellow skin', 'derma' is a noun rather than an adjective and would not therefore be made to agree with Agaricus; Agaricus xanthoderma features include white to grayish or tan cap, sometimes breaking up into scales; tendency of all parts to stain bright yellow; free, close, gills that are white then pinkish or grayish pink then chocolate brown to blackish brown; smooth or nearly smooth stem; membranous ring; and variable habitat; Isaacs recorded a collection from OR, Kerrigan(1) describes as fairly common in CA, Schalkwijk-Barendsen gives range as Pacific Northwest from YT to CA, Lowe reported it from BC, Breitenbach(4) give distribution as North America, Europe, and North Africa, Kerrigan(2) uses collections from CA, France, Spain, and United Kingdom, CHEMICAL REACTIONS cap surface yellow with KOH (Arora)
6-15(20)cm across, spherical to somewhat marshmallow-shaped or convex, then expanding to broadly convex or flat, "margin inrolled somewhat when young and often lobed"; cap "pure white to gray or grayish-buff, or often whitish at the margin and buff to tan toward the center", often discoloring brownish in old age, "typically staining bright yellow quickly when rubbed repeatedly, especially on margin, but then slowly discoloring brownish or vinaceous"; dry, smooth, sometimes breaking up into scales, (Arora), 7-13(18)cm across, hemispheric to somewhat cuboidal, later convex, finally broadly convex, often somewhat undulating [wavy]; white, disc (or sometimes larger area) often near drab to tan, quickly becoming bright yellow when cut or bruised; dry, bald to innately fibrillose, "or occasionally obscurely finely appressed-fibrillose-squamulose", or cracking and becoming scaly under dry conditions, (Kerrigan(1)), cap margin exceeding gills (Isaacs)
thick, firm; white, bruising yellowish when crushed, (Arora), up to 1.5cm thick; white, becoming yellow near cap surface when sectioned, in stem lustrous and whitish becoming yellowish (to yellow at base) when sectioned, (Kerrigan(1))
free at maturity, close; at first white, then pinkish or grayish-pink, finally chocolate brown to blackish brown, (Arora), free, close, up to 1cm broad; pallid at first, then (at least sometimes) becoming flesh-pink, finally dark blackish brown, (Kerrigan(1)), pallid whitish at first, then light chocolate brownish, not vinaceous pink in the Oregon collection, (Isaacs)
5-12(18)cm x 1-2(3)cm, equal or with an widened base, stuffed or hollow; white, usually bruising yellow then brownish, when old often discolored brownish, stains bright yellow when cut in very base; smooth, without scales, (Arora), 5-11cm x 1-2cm, equal or bulbous, to 3cm wide at base, stem stuffed-hollow, base somewhat deeply rooted in soil and/or litter; stem white, becoming bright yellow when cut or bruised; bald in upper part, minutely fibrous in lower part, (Kerrigan(1))
membranous, white or yellow-stained, usually with patches on underside; forming a large, thick, feltlike, median to superior ring, (Arora), veils forming an ample, semi-thick, broadly flaring, pendant, subapical (to supramedian), white ring, upper surface smooth, partial veil 0.1-0.2cm thick, lower surface floccose to coactate and uneven, becoming off-white to pale brownish, or smooth if universal veil remaining entire and partial and universal veils not separating; universal veil typically entire, nearly appressed to stem, pendant from partial veil, or forming large, 0.1-0.3cm thick, variously shaped universal veil remnants, some veil fibrils also sometimes present on stem below ring, (Kerrigan(1)), ring large with cogwheel underneath (Courtecuisse)
unpleasant, phenolic, (Arora), phenolic (Kerrigan(1)), strong, inky or phenolic (Phillips), iodoform or ink (Courtecuisse)
strongly almond-like and disagreeable (Isaacs), similar to odor (Phillips)
Microscopic spores:
spores 4.5-6 x 3-4.5 microns, elliptic, smooth, (Arora), spores (4.1)5.0-5.4(6.4) x (3.0)3.5-4.4(4.5) microns, broadly elliptic to elliptic, dark brown, hilar appendix usually not prominent, germ pore not evident; basidia 4-spored, 20-26 x 6-7 microns, cylindroclavate, sterigmata 3-4 microns long; cheilocystidia scattered, 16-30 x 4-14 microns, cylindric, clavate, ovoid, or spheropedunculate, gill edge essentially sterile, (Kerrigan(1))
Spore deposit:
chocolate brown (Arora)

Habitat / Range

scattered to densely gregarious "under trees and hedges, in yards, on lawns, along roads and paths, also in woods, pastures, and under cypress", (Arora), subcespitose under Pinus ponderosa (Ponderosa pine) in grass and needles (Isaacs for Oregon specimen), gregarious to densely gregarious under Cupressus (cypress), Pinus (pine), Cedrus (true cedar), Acacia, Quercus (oak), Olea (olive), and occasionally other woody plants, or in lawns, (Kerrigan(1) for California), summer and fall (Miller)

Taxonomic and Nomenclatural Links

Additional Range and Status Information Links


poisonous to many, headaches, vomiting, diarrhea, (Arora), causes "sweating, nausea, and severe stomach cramps, though some people are unaffected", (Phillips)

Additional Photo Sources

Related Databases

Species References

Kerrigan(1) (as A. xanthodermus), Kerrigan(2), Arora(1) (as A. xanthodermus), Miller(14)*, Phillips(1)*, Kibby(1)* (as A. xanthodermus), Schalkwijk-Barendsen(1)* (as A. xanthodermus), Lincoff(1)* (as A. xanthodermus), Courtecuisse(1)*, Lowe(1) (as A. xant

References for the fungi

General References