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Agaricus andrewii

[ Basidiomycota > Agaricales > Agaricaceae > Agaricus . . . ]

by Michael Kuo

One of several primarily eastern North American versions of "Agaricus campestris," Agaricus andrewii can be separated by its spores, which generally fall in the 7–8 µm range, length-wise. Like other species in the group it grows in grass and features a whitish cap, gills that progress from pink to brown, and a pointed stem base. By maturity the ring is usually collapsed and not prominent.

Agaricus andrewii was originally described from North Carolina by Freeman (1979), but study of her type collection by Kerrigan (2016) indicates that the collection was actually mixed, and also included a specimen of Agaricus argenteus, which has larger spores, resulting in inaccurate spore measurements in her original account.


Ecology: Saprobic; growing gregariously, or in arcs or fairy rings, in grass; fall; possibly widely distributed from the Great Plains eastward. The illustrated and described collection is from Illinois.

Cap: 4–10 cm; convex or a little blocky at first, becoming broadly convex; dry; minutely radially fibrillose or nearly bald; whitish; not bruising.

Gills: Free from the stem; close; short-gills frequent; brownish pink when young, becoming dark brown; when in the button stage covered with a whitish partial veil.

Stem: 3–6 cm long; 1–2 cm thick; equal above a tapered base; more or less bald; with a fragile, collapsing, white ring; whitish, discoloring a little brownish but not truly bruising; basal mycelium white.

Flesh: White; unchanging when sliced.

Odor and Taste: Not distinctive.

Dried Specimens: Cap and stem dull orangish yellow.

Chemical Reactions: KOH negative on cap surface.

Spore Print: Dark brown.

Microscopic Features: Spores: (6–) 7–8 (–8.5) x 4–5 µm; ellipsoid; smooth; thick-walled; brown in KOH; brown in Melzer's. Basidia 4-sterigmate. Cheilocystidia not found. Pleurocystidia not found. Pileipellis a cutis; elements 2.5–10 µm wide, smooth, hyaline in KOH.

REFERENCES: A. E. Freeman, 1979. (Freeman, 1979; Phillips, 1991/2005; Kerrigan, 2016.) Herb. Kuo 09290505.

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Agaricus andrewii

Agaricus andrewii

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Kuo, M. (2018, April). Agaricus andrewii. Retrieved from the MushroomExpert.Com Web site: