Common Name: death cap
Cap 3.5-15 cm broad, convex, expanding to nearly plane, at maturity the disc sometimes slightly raised or depressed; margin entire, seldom striate, or if so, obscurely so; surface subviscid when moist, smooth, occasionally with a faint, appressed, white universal veil patch; color: olive, olive-brown, to yellowish-brown, rarely white, typically with innate, darker streaks, the margin paler, fading overall to dull tan in age; flesh soft, white, moderately thick at the disc, unchanging, at times yellowish-brown just below the cuticle; odor slightly pungent; taste mild.
Gills free, close, moderately broad, white becoming cream, staining pink to vinaceous with concentrated sulfuric acid.
Stipe 4-18 cm long, 1-3 cm thick, equal to tapering to an enlarged, sometimes bulbous base, usually solid but the apex sometimes stuffed; surface finely striate at the apex, otherwise smooth or with scattered, flattened small scales, white to pale yellowish; flesh white, firm, unchanging; partial veil membranous, cream-colored to tinged like the cap, the upper surface striate, lower surface slightly pubescent, forming a pendulous, superior annulus; volva membranous, thin, white, sac-like, usually erect from the stipe.
Spores 7-12 x 6-10 µm, ovoid to elliptical, amyloid; spore print white.
Solitary, scattered, to gregarious under Coast Liveoak (Quercus agrifolia), occasionally with other oaks and ornamental hardwoods; fruiting sporadically during the summer months in watered areas or from fog drip along the coast; common from early to mid-winter.
Deadly poisonous! A. phalloides contains both phallotoxins and amanitins. It is the amanitins that are responsible for the poisonings in humans. Amanitins are cyclic octapeptides that stop protein synthesis in the cells they encounter. All human organs are effected, but damage to the liver is most severe and liver failure is primarily responsible for the death of A. phalloides victims. Symptoms usually appear 8-12 hours after ingestion. Death occurs in 7-10 days in 10-15% of patients.
A large, handsome mushroom, the Death Cap is often abundant under oaks in the Bay Area, especially in warm, wet years. Because of its toxicity, it should be one of the first mushrooms learned. Fortunately, Amanita phalloides is distinctive and with experience, easily identified. Important field characters are the smooth, yellowish-green to yellowish-brown cap, sometimes with a thin, appressed white universal veil patch, usually non-striate cap margin, free, cream-colored gills, normally solid, not hollow stipe, pendulous annulus, and thin, white, membranous, sac-like volva. The Death Cap is found widely in coastal areas as well as inland at low elevations. A rare, white form of this mushroom, var. alba resembling the Death Angels of the Eastern U.S (Amanita verna, A. virosa ), also occurs in the Bay Area. Another lethal Amanita found locally is Amanita ocreata. Cream-colored, and similar in appearance to the Death Cap, it fruits under coast liveoak (Quercus agrifolia) during the spring.