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Summary: This is the cultivated mushroom sold in supermarkets. Features include white cap usually with flat, brown fibrils that break up into scales; slightly reddening flesh; free, close, pinkish or pale brown gills (when young); a well developed intermediate ring; growth in rich soil or manure (normally not grass); chocolate- or violet-brown spore deposit; and 2-spored basidia. Agaricus hortensis refers to the white form. Kerrigan says Agaricus brunnescens Peck may or may not be conspecific with A. bisporus. Agaricus bisporus has been collected in BC, WA, ID, CA, and probably more widely in the Pacific Northwest, at least as an escaped species. Breitenbach(4) give the distribution as North America, Europe, Asia, and North Africa.
Cap: 3-16cm across, convex becoming flat or slightly depressed, margin inrolled when young, often extending past gills; white, usually with flattened pale brown to brown fibrils that break up into scales; dry, (Arora), 4-16cm across, at first hemispheric with strongly inrolled margin, finally nearly flat or depressed centrally; pallid at first, soon becoming light to medium brown, rarely darker brown, background color whitish to pale vinaceous; dry, at first innately fibrillose, later with appressed-fibrillose fine scales (about 0.2-0.8cm broad), or occasionally remaining loosely interwoven (for example if beneath duff or soil), (Kerrigan), margin appendiculate (Courtecuisse)
Flesh: thick, firm; white, usually becoming brownish to reddish or pinkish orange when cut and rubbed repeatedly, (Arora), up to 2.5cm thick, moderately firm; white, usually somewhat rufescent [becoming somewhat reddish] near gills and cuticle, in stem white, slightly to moderately rufescent [becoming reddish], (Kerrigan)
Gills: free when mature, close; pinkish or pale brown, becoming purple brown to chocolate brown when old, finally blackish brown, (Arora), free, close, up to 1.2cm broad; often pinkish when young, when old dark blackish-brown, margin pallid, (Kerrigan)
Stem: 2-8cm x 1-3(4)cm, equal or enlarged at base, firm, usually stout; white, sometimes turning dingy brownish when old; "smooth or slightly cottony-scaly below ring", (Arora), 3-8cm x 1-3cm, equal to slightly bulbous, stuffed-hollow; white, becoming slightly reddish-orange when cut; bald, (Kerrigan)
Veil: membranous, cottony, white, 2-layered, forming delicate, median to superior ring which may collapse when old, ring intermediate or sometimes skirt-like, upper surface often striate, (Arora), veils forming thick, wedge-shaped, median, white ring, striate on upper surface, lower surface loosely interwoven, entire or grooved between partial veil and universal veil, or in high humidity partial veil long remaining attached to cap margin and expanding to appear pendant, the universal veil then pendant from partial veil, appressed to stem or not, or on rare occasions universal veil and partial veil peronate, (Kerrigan), the undersurface with wide toothed flaps that separate from surface and point down the stem, (Chariton)
Odor: mild or faintly fruity (Arora), fruity/spicy after exposure, (Kerrigan), pleasant (Lincoff), fungoid (Isaacs)
Taste: pleasant (Lincoff)
Microscopic spores: spores 5.5-8.5 x 4-6.5 microns, elliptic, smooth, basidia mostly 2-spored, (Arora), spores (4.9)6.3-7.6(9.0) x (4.5)4.9-5.9(7.1) microns, broadly elliptic to elliptic, dark brown, hilar appendix often prominent, germ pore not evident; basidia predominantly 2-spored, 17-22 x 4-5 microns, cylindroclavate; cheilocystidia forming a continuous band, 20-35 x 6-10.5 microns, clavate or clavate-truncate, (Kerrigan), spores 5.9-7.7(8.3) x 5.3-6.5 microns, round to broadly elliptic or obovate in both views, apiculus short, blunt, colorless, one to several droplets; basidia 2-spored, 19-25 x 6.5-9 microns, clavate to broadly clavate, with a broad pedicel, colorless, sterigmata 3.5-7 microns long, aculeate to narrowly acuminate; cheilocystidia forming nearly sterile edge, clustered, or scattered with occasional basidia, 12-32 x 7-12 microns, clavate, cylindric, broadly clavate or occasionally spheropedunculate, cylindrofusoid or saccate, often repent, colorless, (Isaacs)
Spore deposit: chocolate brown (Arora) cocoa-brown or violet-brown (Lincoff)
Habitat / Range
in grocery stores, compost, manure, rich soil, along paths, in gardens, rarely in woods or on lawns, (Arora), gregarious to cespitose [in tufts], or rarely single, "in old manure or manured ground or compost, or in old piles of plant trimmings and sludge, or in litter of trees", especially Cupressus macrocarpa (Monterey cypress), occasionally under Pinus (pine), Eucalyptus, Quercus (oak), and others, (Kerrigan for California), spring, summer, fall (Buczacki)
Agaricus bisporus is like A. campestris but the basidia of A. bisporus are mostly 2-spored, the ring is well-developed, the cap is browner, the flesh is slightly reddening, and it rarely grows in grass. A. californicus is more slender (stem 0.5-1(1.5)cm instead of 1-4cm), usually has phenolic odor at least when cooked, has pallid or whitish gills at button stage before veil breaks, rarely fruits in manure or compost, and has a cap surface that yellows in KOH (rarely slightly in A. bisporus).
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:
2020-02-27 5:05:27 PM
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