Synonym: Amanita bivolvata Peck
Cap 5-13 cm broad, convex, expanding to plano-convex; margin decurved, often plane at maturity, not striate, or if so, obscurely; surface nearly smooth, sticky when moist; color: pallid to cream, sometimes with pinkish tones; universal veil patch usually lacking, or if present, thin, appressed, whitish to buff; context moderately thick, firm, white, yellowing in KOH; odor mild at first, of fish in age; taste, mild.
Gills adnexed, crowded when young, close in age, moderately broad, white to cream.
Stipe 10-22 cm tall, 1.5-3.0 cm thick, round, usually stuffed at maturity, the base bulbous; surface white, scurfy or with fine appressed scales at the apex, scattered fibrils to smooth below; partial veil thin, membranous, pallid, upper surface faintly wrinkled, lower surface cottony, forming an evanescent, ragged, superior ring, often collapsing against the stipe; volva membranous, thin, white, sac-like, erect or flattened against the stipe base.
Spores 9-12.5 x 7-9 µm, subglobose to oval, smooth, thin-walled, amyloid; spore print white.
Solitary to scattered under Coast Liveoak (Quercus agrifolia); fruiting from late winter to spring.
Deadly poisonous. Contains amanitoxins.
Like its cousin Amanita phalloides (Death Cap), Amanita ocreata is a dangerously toxic species. Both species occur under coast liveoak (Quercus agrifolia) but at different seasons, Amanita phalloides in the fall, A. ocreata in the late winter and spring. Unlike the Death Cap, Amanita ocreata is seldom abundant which probably explains why relatively few Bay Area mushroom poisonings have been attributed to it. Amanita ocreata is a large, attractive mushroom recognized by a cream-colored, non-striate cap, bulbous base subtended by a thin, white membranous volva , and a fragile, white annulus. Dilute potassium hydroxide, which yellows the cap cuticle and context, will help to confirm an identification. Look-alikes include pale specimens of Volvariella speciosa, a harmless mushroom distinguished by the lack of an annulus and salmon-pink spores, and white forms of Amanita lanei and A. velosa. The latter two species are edible but should be avoided by all but the experts because of possible confusion with Amanita ocreata and A. phalloides.