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Agaricus moronii

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

by Michael Kuo

This western, montane species is found under conifers at higher elevations, and can be recognized by its bald, whitish cap, its yellow staining (rub the edge of the cap with your thumb), its almondy odor—and especially by its stem, which ends somewhat abruptly and terminates in a squarish or slightly flared base. The stature of Agaricus moronii is often a little bit stocky, since the stem is usually not longer than the width of the cap at maturity.

Agaricus moronii is named for the location of its type collection, in the mountains near Moroni, Utah. It was recently described as a new species by Kerrigan (2016), but has often passed as "Agaricus albolutescens" in herbaria and field guides; Kerrigan limits the true Agaricus albolutescens to coastal California and Oregon. Agaricus summensis is similar to Agaricus moronii and is also sometimes found in montane ecosystems, but features a fibrillose, darker-staining cap, and a stem base that is often narrowed and pointed.


Ecology: Saprobic; growing gregariously under spruces and firs; late summer; probably distributed throughout the western North American mountains. The illustrated and described collections are from Colorado.

Cap: 6–10 cm; convex, becoming broadly convex or nearly flat; dry; bald; whitish, becoming streaked with brassy orangish, or dull yellowish overall with age; bruising bright yellow when rubbed, especially near the margin.

Gills: Free from the stem; nearly crowded; short-gills frequent; whitish when very young, becoming dark brown at maturity; when in the button stage covered with a whitish partial veil.

Stem: 7–10 cm long; 2–2.5 cm thick; more or less equal above a somewhat abruptly terminating, squarish base; more or less bald; with a thick, whitish, skirtlike ring that may stain yellow; whitish, bruising yellow, especially at the base.

Flesh: White; changing to yellow in the stem base when sliced.

Odor and Taste: Odor strong, reminiscent of almonds, becoming foul with age; taste similar.

Dried Specimens: Cap and stem dull orangish yellow.

Chemical Reactions: KOH yellow on cap surface.

Spore Print: Dark brown.

Microscopic Features: Spores: 6–8 x 4–5 µm; ellipsoid; smooth; thick-walled; brown in KOH; brown in Melzer's. Basidia 4-sterigmate. Cheilocystidia 15–25 x 7–9 µm; clavate to subclavate; catenulate; smooth; thin-walled; hyaline in KOH. Pleurocystidia not found. Pileipellis a cutis.

REFERENCES: R. Kerrigan, 2016. (Kerrigan, 2016.) Herb. Kuo 07281903. Herb. DBG ROMO 2012 5022-07.

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Agaricus moronii

Agaricus moronii

Agaricus moronii

Agaricus moronii

Agaricus moronii

Agaricus moronii

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Kuo, M. (2019, December). Agaricus moronii. Retrieved from the MushroomExpert.Com Web site: