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Agaricus californicus

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

by Michael Kuo

Found in lawns and other grassy areas in California and in central Mexico, Agaricus californicus is similar in appearance to Agaricus campestris, which also grows in lawns and features pink-then-brown gills. However, despite superficial resemblance, the two species are not particularly closely related—and closer inspection reveals that Agaricus californicus has a browner cap, a thicker, more persistent ring, a yellow reaction to KOH, and smaller spores.

Thanks to Mila Visser 't Hooft for collecting, documenting, and preserving Agaricus californicus for study; her collection is deposited in The Herbarium of Michael Kuo.


Ecology: Saprobic; growing gregariously in lawns and other grassy areas, sometimes in the vicinity of oaks or Monterey cypress; fall and winter; originally described from Pasadena; fairly widely distributed in California; also found in central Mexico. The illustrated and described collection is from California.

Cap: 3–7 cm across; convex with an inrolled margin at first, expanding to broadly convex; dry; bald or a little bit appressed-fibrillose or scaly over the center; not yellowing when rubbed near the margin.

Gills: Free from the stem or nearly so; close; short-gills frequent; whitish in buttons, becoming pink, and then dark brown in maturity; covered with a white partial veil when in the button stage.

Stem: 4–9 cm long; 1–1.5 cm thick; equal; more or less bald; with a thick, felty, white ring; whitish; not bruising, or bruising slightly yellow at the base; basal mycelium white.

Flesh: White; firm; unchanging when sliced, or becoming yellowish in stem base.

Odor: Mildly phenolic.

Dried Specimens: Brownish and brown, without yellow or orange shades.

Chemical Reactions: KOH yellow on cap surface.

Spore Print: Dark brown.

Microscopic Features: Spores: 5–7 x 4–5 µm; ellipsoid; smooth; thick-walled; brown in KOH. Basidia 22–26 x 4–5 µm; subclavate; 4-sterigmate. Pleurocystidia not found. Cheilocystidia to 22 x 6 µm; clavate; smooth; thin-walled; hyaline in KOH. Pileipellis a cutis; elements 5–12.5 µm wide, smooth, hyaline to brownish-walled in KOH.

REFERENCES: C. H. Peck, 1895. (Arora, 1986; Kerrigan, 1986; Lincoff, 1992; Kerrigan et al., 2005; Desjardin, Wood & Stevens, 2015; Kerrigan, 2016; Siegel & Schwarz, 2016.) Herb. Kuo 09182001.

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Agaricus californicus

Agaricus californicus

Agaricus californicus

Agaricus californicus

Agaricus californicus

Agaricus californicus

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Kuo, M. (2021, March). Agaricus californicus. Retrieved from the MushroomExpert.Com Web site: