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Agaricus julius

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

by Michael Kuo

This recently named species is the Rocky Mountain version of the well-known West-Coast species Agaricus augustus. Like its West-Coast counterpart it has a large cap adorned with brown scales, and a strong odor, reminiscent of almonds. However, its young cap is more rounded (the cap of Agaricus augustus is often blocky when young), and it appears in high-elevation spruce-fir forests (Agaricus augustus appears under coastal conifers, usually in urban or semi-urban locations). Agaricus guru Rick Kerrigan (2016) documents a difference in spore size between the two species (slightly larger for Agaricus julius); however, the Colorado collections I have studied have not borne out this difference.

Since Agaricus julius has been identified as Agaricus augustus by Rocky Mountain collectors for decades, and since Agaricus augustus is often given the common name of "The Prince," Kerrigan suggests that Agaricus julius might now become "the Emperor formerly known as Prince" (2016).

Thanks to the Sam Mitchel Herbarium of Fungi at the Denver Botanic Gardens for facilitating my study of the Agaricus julius collections cited and described below, and for permission to reproduce the collectors' photos.


Ecology: Saprobic; growing scattered, gregariously, or in small groups; late summer and early fall; distributed in the Rocky Mountains from New Mexico to Alaska. The illustrated and described collections are from Colorado.

Cap: 8–15 cm; convex at first, becoming broadly convex with a flattened center; dry; covered with appressed fibrils that break up into fibrillose scales; fibrils and scales tawny brown; base color ivory white; at first evenly covered but darker over the center and paler elsewhere at maturity.

Gills: Free from the stem; crowded; short-gills frequent; grayish, becoming medium to dark brown (without a pink stage); when in the button stage covered with a thin, white partial veil.

Stem: 8–17 cm long; 1.5–3 cm thick; equal or slightly swollen toward the base, which is often deeply sunken in the substrate; scurfy below the ring; with a thick white ring; brownish.

Flesh: White; unchanging when sliced, or becoming slightly brownish in the stem base.

Odor and Taste: Odor of almonds; taste pleasant.

Dried Specimens: Cap and stem dull orangish.

Chemical Reactions: KOH yellow on cap and stem surfaces.

Spore Print: Dark brown.

Microscopic Features: Spores: 7–9 x 5–6 µm; ellipsoid; smooth; thick-walled; brown in KOH; brown in Melzer's. Basidia 4-sterigmate. Cheilocystidia 10–20 µm; subglobse; smooth; thin-walled; hyaline in KOH. Pleurocystidia not found.

REFERENCES: R. Kerrigan, 2016. (Kerrigan, 2016.) Herb. DBG 3585, 6015.

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Agaricus julius

Agaricus julius

Agaricus julius

Agaricus julius
Dried specimens

Agaricus julius

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