Agaricus hondensis — Felt-ringed agaricus

Odour: Mild or faintly phenolic, but the base of the stem of a mature or old mushroom, if squeezed, usually smells strongly like phenol or creosote.
Cap: 4–15 cm wide, first hemispherical, then opening to become convex or almost flat. Cap white to cream, darker in centre and darkening also with age. Caps may be smooth, or with delicate beige or pinkish fibrils that are pressed closely to the cap surface. Flesh is firm, white and solid5.
Gills: Free, crowded, initially light gray to pink, turning chocolate brown as the mushroom ages.
Stem: 4.5-15 cm long, 1.5-4 cm wide at the top, almost always expanding to a base that is club-like and 2-3 cm wide. Smooth, white. It may develop yellowish stains if scratched, especially at its base.
Ring or veil: White, forming a stiff felt-like ledge that usually flares out around the stem. The ring is almost perpendicular to the stem, collapsing only when the mushroom is old.
Cup: None.
Spores: 4.5-6 x 3-4 µm 2, ellipsoid, smooth, purplish-brown6.
Habitat: On the ground, a forest species, under Douglas fir (Pseudotsuga menziesii), western red cedar (Thuja plicata) and other conifers in the Pacific northwest1, occasionally also under hardwoods, and in California, under redwoods3, saprotrophic.
Geographic range: Western North America1.

Many other Agaricus species including the common grocery store button mushroom can resemble the felt-ringed agaricus in cap and gill colour. Its stiff, thick ring that flares out horizontally helps distinguish this species from many others. Any Agaricus that smells like phenol or creosote is likely to be poisonous.

Toxins: Contains hydroquinone8, gastrointestinal irritant.

Symptoms: Time of onset 15 min to 1 hour; nausea, vomiting, watery to bloody diarrhoea, abdominal pain, muscle pain. Symptoms usually do not last longer than 24 hours.

Treatment: Contact your regional Poison Control Centre if you or someone you know is ill after eating any Agaricus species. 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.

MyCoPortal. Mycology Collections Portal, <> accessed March 2018.

Specimen Agaricus hondensis. UBC F25680 MO 291671, GenBank #MF954614.

Kerrigan, R. W. Agaricus of North America. Memoirs of The New York Botanical Garden Vol. 114, NYBG Press, Bronx, New York (2016).

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).

Trudell, S., Ammirati, J. F. & Mello, M. Mushrooms of the Pacific Northwest. Timber Press, Portland, Oregon (2009).

Murrill, W. A. The Agaricaceae of the Pacific Coast: III. Mycologia 4, 294-308, doi:10.2307/3753286 (1912).

Leikin, J. B. & Paloucek, F. P. Poisoning and Toxicology Handbook, 4th ed., CRC Press, Boca Raton, Florida (2008).

Jovel, E., Kroeger, P. & Towers, N. Hydroquinone: the toxic compound of Agaricus hondensis. Planta Medica 62, 185 (1996).