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Summary: Agaricus campestris is identified by its stature, its white (or occasionally appressed brown scaly) cap, its flesh with no yellow change on injury, the bright pink gills, and a thin often fleeting ring. One variation (var. lutescens nom. prov.) stains yellow when bruised (although the flesh of the stem still does not change when cut), and this variety has smaller spores (4.7)5.4-6.5 x 4-4.7 microns, (Isaacs(1)). Agaricus campestris is common in Pacific Northwest, and is mentioned specifically for BC (Redhead(5)), CA (Arora), and WA (M. Beug, pers. comm.). There are collections at Oregon State University from OR, and it also occurs elsewhere in North America, in Europe, and in N. Africa., CHEMICAL REACTIONS not yellowing with KOH (Arora)
Cap: 4-11(15)cm across, convex or dome-shaped for a long time, then often becoming flat; "pure white, or sometimes with a few grayish to brown or cinnamon-buff fibrils or fibrillose scales"; dry, smooth or silky-fibrillose, margin extending beyond gills, "often hung with veil remnants", (Arora), (2)3-7(10)cm across, obtuse to convex, expanding to broadly convex to flat or at times the disc slightly depressed when old; pure white in one form but becoming pinkish to vinaceous brown or finally dull purplish brown when old at least over marginal area, "in a second form the fibrils more or less cinnamon-brown even on buttons and retaining these colors" (but with the flesh gradually darkening as in the white form); dry, innately fibrillose to appressed silky-fibrillose, nearly bald at first, "the fibrils often loosening and becoming aggregated into appressed scales, the scales either white or becoming cinnamon to reddish brown", disc sometimes areolate [cracked like dried mud] and margin torn into imbricate [shingled] scales from the splitting of the cuticle and flesh, (Smith)
Flesh: thick; white, not bruising but sometimes staining brownish or reddish when old or in wet weather (especially just above the gills), (Arora), soft to rather firm; "white to pallid vinaceous or finally darker", (Smith)
Gills: free at maturity, close; pale pink in button stage, then bright pink becoming purple-brown to chocolate brown and finally blackish brown with spores, (Arora), free, crowded, narrow, 0.5-0.6cm broad, usually not reaching the margin of the cap; pallid pink, becoming bright pink before veil breaks, dark purplish brown when old; edges even, (Smith)
Stem: 2-6(10)cm x 1-2.5cm, usually with a tapered base, firm, stuffed or hollow; white; smooth above the veil, often with a few fibrils below, (Arora), 2-4(6)cm x 1-1.5cm, "equal, subventricose or narrowed at base, stuffed and becoming hollow, white and silky above the ring but soon tinged pink and finally sordid vinaceous brown, below the annulus more or less white-fibrillose, glabrescent, white at first but finally discoloring to dull vinaceous brown", (Smith)
Veil: thin, somewhat cottony, white, forming a thin ring on stalk or leaving remnants on cap margin or disappearing entirely; ring rarely well-formed, intermediate (sometimes flaring) or rarely skirtlike, median to superior, (Arora), ring thin, single, membranous but often torn and frequently fleeting, sometimes most of veil adhering to cap margin, (Smith)
Odor: mild (Arora), none or slight (Smith), pleasant (Phillips), mild almond (Chariton)
Taste: slightly of almonds (Smith), pleasant (Phillips), mild (Miller)
Microscopic spores: spores 6.5-8.5 x 4-5.5 microns, elliptic, smooth, basidia mostly 4-spored, (Arora), spores 6-7.5 x 4.5-5 microns, elliptic to subovoid, smooth, dark chocolate brown in KOH; basidia both 4-spored and 2-spored in a given cap (the former abundant, the latter rare), 20-24 x 7-8 microns, colorless in KOH; pleurocystidia none, cheilocystidia basidia-like or an occasional cystidium greatly enlarged (up to 20 microns broad); no clamp connections, (Smith)
Spore deposit: chocolate brown (Arora), dark chocolate brown (Miller)
Habitat / Range
in groups or fairy rings or occasionally single; in grass, (Arora), scattered to gregarious or subcespitose [more or less in tufts] "in meadows, pastures, along roads and in barnyards", (Smith), "spring and fall or during periods of cool moist weather at other times", (Miller), spring, summer, fall, winter
Pink gills (becoming chocolate-brown from spores) are the best distinguishing mark from non-Agaricus species like Amanitas. Agaricus californicus (which often grows with it) has a more persistent membranous veil and whitish gills in button stage. Agaricus cupreobrunneus (common in California) is smaller, browner and (when young) fuzzier. The cultivated Agaricus bisporus has basidia that are mostly 2-spored, a well-developed ring, a browner cap, and slightly reddening flesh, and it rarely grows in grass.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Flora BC:
Electronic Atlas of the Plants of British Columbia [eflora.bc.ca]. Lab for
Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
20/10/2019 7:07:02 AM
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