Domain: Eukarya
Kingdom: Fungi
Phylum: Basidiomycota
Class: Agaricomycetes
Order: Agaricales
Family: Agaricaceae
Genus: Agaricus

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”¹, (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 mud] and margin torn into imbricate [shingled] scales from the splitting of the cuticle and flesh⁶.

FLESH: thick; white, not bruising but sometimes staining brownish or reddish when old or in wet weather (especially just above the gills)¹, soft to rather firm; “white to pallid vinaceous or finally darker”⁶.

GILLS: free at maturity, close; pale pink in button stage, then bright pink becoming purple-brown to chocolate brown and finally blackish brown with spores¹, 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 even⁶.

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 below¹, 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”⁶.

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”¹, ring thin, single, membranous but often torn and frequently fleeting, sometimes most of veil adhering to cap margin⁶.

ODOR: mild¹, none or slight⁶, pleasant⁵, mild almond²

TASTE: slightly of almonds⁶, pleasant⁵, mild⁴

SPORE DEPOSIT: chocolate brown¹, dark chocolate brown⁴

CHEMICAL REACTIONS: not yellowing with KOH¹

MICROSCOPIC: spores 6.5-8.5 × 4-5.5 microns, elliptic, smooth, basidia mostly 4-spored¹, spores 6-7.5 × 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 × 7-8 microns, colorless in KOH; pleurocystidia none, cheilocystidia basidia-like or an occasional cystidium greatly enlarged (up to 20 microns broad); no clamp connections⁶.

Identified by stature, white (or occasionally appressed brown scaly) cap, flesh with no yellow change on injury, bright pink gills, and thin often fleeting ring; one variation (var. lutescens nom. prov.) stains yellow when bruised but flesh of stem still unchanging on cutting, and has smaller spores (4.7)5.4-6.5 × 4-4.7 microns³.

Agaricus campestris common in many regions of North America, Europe and N. Africa

In groups or fairy rings or occasionally single; in grass¹, scattered to gregarious or subcespitose [somewhat tufted] “in meadows, pastures, along roads and in barnyards”⁶, “spring and fall or during periods of cool moist weather at other times”⁴.

Pink gills (becoming chocolate-brown from spores) are the best distinguishing mark from non-Agaricus species like Amanitas; Agaricus californicus (often grows with it) has a more persistent membranous veil and whitish gills in button stage; A. cupreobrunneus (common in California) is smaller, browner and (when young) fuzzier; like cultivated A. bisporus but basidia of A. bisporus mostly 2-spored, ring well-developed, cap browner, flesh slightly reddening, rarely grows in grass

A choice and popular edible¹⁶

¹ Arora, David. 1986 Mushrooms Demystified Second Edition. Ten Speed Press, Berkeley.

² Chariton, Laverne R. 1997. A trial field key to the species of the genus Agaricus of the Pacific Northwest. Pacific Northwest Key Council.

³ Isaacs, Bill Forgust. 1963. A Survey of Agaricus in Washington, Oregon, and California. Thesis for Master of Science, University of Washington.

⁴ Miller Jr., Orson K., Hope H. Miller. 2006. North American Mushrooms. A field guide to edible and inedible fungi. Falcon Guide.

⁵ Phillips, Roger. 1991. Mushrooms of North America. Little, Brown, & Co., Boston.

⁶ Smith, A.H. Mushrooms in Their Natural Habitats. University of Michigan Press, Ann Arbor.

“Common Name: Meadow Mushroom” Pink Bottom, Pinky

Name origin: means “of the plains”
Adapted from the description in the MatchMaker database. Used with permission.