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Agaricus xanthodermus

[ Basidiomycetes > Agaricales > Agaricaceae > Agaricus . . . ]

by Michael Kuo

This fairly common Agaricus species is impressive, and often fruits in large numbers in grassy areas and areas of landscaping debris. It is distinguished from similar mushrooms, like Agaricus campestris, by its tendency to stain and bruise yellow and by its characteristic odor, which is phenolic. To see the yellow staining and bruising, rub the mushroom with your thumb--especially near the cap margin and the base of the stem. Importantly, the surfaces that have bruised yellow eventually turn brownish, helping to distinguish this mushroom from others that bruise yellow and remain yellowed. When sliced open, the flesh in the stem base is bright yellow. The phenol smell is sometimes faint, and is best detected by crushing the base of the stem.


Ecology: Saprobic; growing scattered or in large groups, sometimes clustered together; in grass and in cultivated areas; occasionally in woods; summer and fall; widely distributed in North America.

Cap: 6-20 cm; round to irregularly convex, becoming broadly convex or nearly flat; whitish, or with light brown colorations, especially towards the center; dry; bald, or with scattered fibrils; 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.

Gills: Free from the stem; white at first, then pinkish, and finally dark chocolate brown; close; when in the button stage, covered with a membranous white or yellowed partial veil that has patches of tissue on its underside.

Stem: 5-18 cm long; 1-3 cm thick; more or less equal; sometimes enlarged at the base; smooth; whitish, bruising yellow (then brownish); sometimes brownish in age; stuffed or hollowing; with a large, flaring, thick, yellow-staining ring on the upper portion.

Flesh: White and thick; yellowing when crushed; bright yellow in the base of the stem when sliced.

Odor and Taste: Odor unpleasant and phenolic, but sometimes faint; crush the flesh in the stem base to be sure.

Chemical Reactions: Cap surface yellow with KOH.

Spore Print: Dark chocolate brown.

Microscopic Features: Spores 4.5-6 x 3-4.5 µ; ellipsoid; smooth.

REFERENCES: Genervier, 1876. (Saccardo, 1887; Arora, 1986; Kerrigan, 1986; Phillips, 1991/2005; Lincoff, 1992; Evenson, 1997; Kerrigan et al., 2005; Miller & Miller, 2006.) Herb. Kuo 08230206, 01130514, 01110606, 06201101, 06201102.

"Agaricus xanthoderma" is an error in Latin agreement found in some sources; Agaricus lepiotoides is a synonym.

Further Online Information:

Agaricus xanthodermus at MykoWeb
Agaricus xanthodermus at Roger's Mushrooms


Agaricus xanthodermus

Agaricus xanthodermus

Agaricus xanthodermus

Agaricus xanthodermus
Flesh in stem base

Agaricus xanthodermus

Agaricus xanthodermus

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Cite this page as:

Kuo, M. (2002, August). Agaricus xanthodermus. Retrieved from the MushroomExpert.Com Web site: