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Agaricus andrewii

by Michael Kuo, 7 November 2022

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; originally described from North Carolina (Freeman 1979); probably widely distributed from the Great Plains eastward. The illustrated and described collections are from Illinois.

Cap: 4–11 cm; convex or a little blocky at first, becoming broadly convex; dry; at first nearly bald, becoming finely radially fibrillose and scaly; whitish, developing dingy yellowish areas; not bruising.

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

Stem: 4–7 cm long; 1.5–2.5 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 and on flesh.

Spore Print: Dark brown.

Microscopic Features: Spores 6–8.5 x 4–5 µm; ellipsoid; smooth; thick-walled; brown in KOH; brown in Melzer's. Basidia 28–32 x 6–9 µm; 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, 11032201.

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Agaricus andrewii

Agaricus andrewii

Agaricus andrewii

Agaricus andrewii

Agaricus andrewii
Spore print

Agaricus andrewii

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