Agaricus placomyces
Description
Agaricus placomyces is a poisonous basidiomycete fungus of the genus Agaricus. Like many species in the genus its cap is brownish, with a darker center. Depending on weather conditions, exposure to sunlight, and idiosyncrasies, the brown covering may break up into aggregations and scales, sometimes exposing a whitish ground color so that the cap appears from a distance to be whitish with a brown center.
The surfaces of Agaricus placomyces bruise yellow when the mushrooms are fresh, and the flesh in the base of the stem is usually yellow when sliced. The odor is phenolic, especially in the base of the stem—but if, like me, you have trouble detecting this odor, never mind.
This mushroom contains toxins that cause gastrointestinal upset, as with other phenolic-odored Agaricus species. Some people reportedly may not be affected. The mushroom's taste is mild and its odor resembles phenol or coal tar.
Common names: Meadow Mushroom, Pink Bottom, Eastern Flat Topped Agaricus.
Mushroom Identification
Cap
5-12 cm, convex to broadly convex or nearly flat in age; dry; covered with brownish fibers and scales, especially over the center; whitish underneath, or pinkish in wet weather.
Gills
Free from the stem; crowded; pale grayish pink, eventually brown.
Stem
6-15 cm long; 1-1.5 cm. thick; more or less equal, or with an enlarged base (but not typically ending in a small bulb-like Agaricus pocillator); fairly smooth; white; bruising yellow, especially at the base; with a persistent ring; the partial veil when still covering the gills developing brownish to yellowish droplets.
Flesh
White throughout, staining bright yellow in the base.
Odor and Taste
Taste not distinctive or somewhat unpleasant; odor usually unpleasant (phenolic), but sometimes not distinctive.
Spore Print
Brown.
Chemical Reactions
Cap yellow with KOH.
Microscopic Features
Spores 5-7 × 3.5-5 µ; broadly elliptical; smooth.
Look-Alikes
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Features darker brown, more prominent scales, a slightly stockier stem, and, under the microscope, sphaeropedunculate cheilocystidia.
Agaricus approximans
Usually a bit smaller (caps 3–10 cm across) and features yellow staining that becomes brownish orange.
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A cup-like bulb at the stem base.
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Usually featuring a small, round bulb
Photo sources:
Photo 1 - Author: wearethechampignons (Public Domain)
Photo 2 - Author: alan_rockefeller (Attribution-ShareAlike 4.0 International)
Photo 3 - Author: alan_rockefeller (Attribution-ShareAlike 4.0 International)