Agaricus augustus — "The prince"

Card image cap

The prince2, photograph by Ludovic Le Renard.

A very good-tasting Agaricus species!

Gills: Free, at first pale, becoming dark brown
Spore print: Dark brown

Left image: The prince, Agaricus augustus8, photograph by David Carmean.
Right image: 'Harvesting young princes'8, photograph by David Carmean.


Odour: Like almond extract or marzipan.
Cap: 9-30 cm in diameter, starting out as a closed roundish box, expanding and finally flat to slightly uplifted and with a wavy margin. As it expands, the cap surface is broken into radially arranged, flat, fibrillose brown scales. The background between scales is white at first, but changes to golden yellow or brown. On bruising, turning yellow to almost orange and keeping that colour. The surface is dry.
Gills: Crowded, free, pale when young, becoming dark brown to almost black.
Stem: 10–35 cm long x 1–5 cm wide, cylindrical, or slightly thinner at apex, often deep in the soil. Above the ring smooth, and below the ring with distinct yellowish fibrous scales. Starting out white, and becoming yellow with age. Hollow.
Ring: Flaring, hanging and white with yellowish square patches of veil on its lower surface towards the edge.
Cup: None.
Spores: 7.5-9.5 x 5-6 µm, smooth, dark brown.
Habitat: On the ground, most often under conifers in various types of forests. Saprophytic.
Geographic distribution: Known from western North America, Europe and north Africa6. Collections from the Rocky Mountains are now called Agaricus julius. Mexican and eastern North American collections under the name A. augustus might also represent a different species4.

The poisonous Smith's amanita, Amanita smithiana also has a scaly stem with a ring around it, sometimes also with yellowish warts on its cap. However, Smith's amanita has white, not dark brown spores and its cap has warts rather than brown, flattish, fibrous scales. Smith's amanita smells of old socks; its wide stem base has a girdle of white material on it; and the base of Smith's amanita extends like a root into the soil (dig deep in the soil to find it).

Agaricus species can be difficult to distinguish and mistaking poisonous for edible kinds is one of the more frequent cases of mushroom-related gastrointestinal distress. Fortunately, poisonous Agaricus species including Agaricus deardorffensis, A. buckmacadooi and A. hondensis lack the combination of the shaggy stem, almond odour, and flat, brownish scales of A. augustus.

Chlorophyllum and Lepiota species can have white caps with brown scales, but they usually have slender stalks relative to overall cap size and they have white spores, unlike the dark spores of the prince.
The prince Agaricus augustus is distinctive because of its size, the yellow-brown scales on the cap, the scaly stem, and the strong odour of almond extract. Agaricus smithii is similar, but the stem is abruptly bulbous, the cap is not as fibrillose-scaly and it is known from Sitka spruce (Picea sitchensis) forests in coastal southern Oregon and northern California.

No known toxins but illnesses among individuals with unusual sensitivities have occasionally been reported. Four adults in Washington state reportedly ate A. augustus and between 2.5 and 6 hours later, they experienced gastrointestinal distress, sweating, sneezing and runny noses7.

Treatment: Contact your regional Poison Control Centre if you or someone you know is ill after eating agaric mushrooms. Poison centres provide free, expert medical advice 24 hours a day, seven days a week. If possible, save the mushrooms or some of the leftover food containing the mushrooms to help confirm identification.

Poison Control:
British Columbia: 604-682-5050 or 1-800-567-8911.
United States (WA, OR, ID): 1-800-222-1222.

1
UBC. University of British Columbia Herbarium Database, <http://bridge.botany.ubc.ca/herbarium/database.php> accessed February 1, 2017.
2
Specimen Agaricus augustus UBC F33016, GenBank #MF954626.
3
Siegel, N. & Schwarz, C. Mushrooms of the Redwood Coast. A Comprehensive Guide to the Fungi of Coastal Northern California. Ten Speed Press, Berkeley, California (2016).
4
Kerrigan, R. W. Agaricus of North America. Memoirs of the New York Botanical Garden Vol. 114, NYBG Press, Bronx, New York. (2016).
5
Trudell, S. & Ammirati, J. F. Mushrooms of the Pacific Northwest. Timber Press, Portland, Oregon (2009).
6
MyCoPortal. Mycology Collections Portal, <http://mycoportal.org/portal/collections/harvestparams.php> accessed February 2018.
7
Beug, M. W., Shaw, M. & Cochran, K. W. Thirty-plus years of mushroom poisoning: Summary of the approximately 2,000 reports in the NAMA case registry. McIlvainea 16, 47-68 (2006).
8
Specimen Agaricus augustus UBC F33028, GenBank #MF954627.