Pileo 60–180 mm lato, hemispherico, dein planoconvexo, glutinoso, flavo, margine striato, cum fragmento volvae magno persistento albo. Lamellis confertis, liberis, albis. Stipite 50– 140 mm longo, cylindrico, albo. Annulo superiore, striato, albo. Volva ampla, membranosa, crassa. Carne albido. Sapore miti. Species vernalis. Sporis 9–12 × 6–7 μm, late ellipsoideis, hyalinis. Basidiis 42–64 × 11–14 μm, tetrasporigeris, fibulis praesentibus.
Type: USA. California: El Dorado County, Georgetown, Dru Barner Campground, under Quercus kelloggii, 21 May 2011, Bojantchev DBB43538 (Holotype UC 1860906; Genbank nrITS JN133297).
Etymology: from the Latin vernus = vernal and coccora = the local name for this mushroom.
Pileus 60–180 mm diam., hemispherical to convex when young, plano-convex to plano-concave with age; margin straight, short striate; color uniform yellow to pale yellow; with a white, monolithic, central velar remnant, cottony thick at first, thinning with age. Lamellae crowded, 10–18 mm broad, white to pale cream, even, seceding to free, lamellulae common. Stipe 50–140 mm long, 15–30 mm wide, cylindrical, white with yellow tints at age, context hollow or stuffed with a cottony or jelly-like substance in buttons. Annulus superior, membranous, pendant, upper surface striate, cottony-thick at first, thinning and collapsing with age, white to pale yellow with age. Volva ample, thick, friable, free, sac-like at first, thinning and collapsing with age, white. Context white to pale yellow. Odor mild at first, pungent with age, frequently interpreted as fishy. Taste mild to pungent. Macrochemical Reactions 5% KOH negative, 10% NH4OH negative, 3% phenol slowly pinkish-lilac on all surfaces, Guaiac negative, 10% FeSO4 negative. Spore Deposit white.
Basidiospores (8.5–)9.2–11.8(–12.5) × (5.7–)6.2–7.1(–7.5) μm (mean 10.5 × 6.5 μm), Q = 1.43–1.77, Qav = 1.61 (N = 183, 5 basidiomata, 4 collections), broadly ellipsoid, with a prominent lateral apiculus, hyaline, inamyloid. Basidia 42–64 × 11–14 μm, 4-spored, clavate, clamped, sterigmata 4–6 μm long. Subhymenial layer composed of several layers of irregular to pyriform cells 10–30 × 8–22 μm, frequently clamped Lamellar trama divergent, composed of filamentous to swollen hyphae 8–24 μm wide, occasionally clamped. Cystidia not observed. Pileipellis an ixocutis to ixotrichoderm, densely interwoven within a gelatinous matrix, 200–320 μm thick, hyphae 2–7 μm wide, branched, clamped, intracellular pigment. Annulus composed of filamentous cells, 2–6 μm wide with clusters of inflated clavate, pyriform or mucronate cells 25–50 × 16–24 μm, mainly on the upper surface. Universal Veil formed of dense filamentous hyphae 1.5–8 μm wide, clamped, interspersed with vesiculose cells on the inner surface: narrow ellipsoid to elongated, 50–120 × 20–50 μm; on the outer surface: broadly ellipsoid to subglobose, 60–180 × 40–150 μm, slightly gelatinized. Stipe Trama acrophysalidic, composed of filamentous hyphae 2–8 μm wide and inflated hyphae 50–150 × 20–46 μm, occasionally clamped.
Habitat and distribution — Amanita vernicoccora fruits in the late winter and spring and is apparently restricted to California. Along the coast and in the lower elevations of Sierra Nevada (Quercus agrifolia Née), interior live oak (Quercus wislizenii A. DC.) and blue oak (Quercus douglasii Hook. & Arn.). Likely associations are also to Pacific madrone (Arbutus menziesii Pursh) and manzanita (Arctostaphylos manzanita Parry). Infrequently, A. vernicoccora fruits in the northern coastal areas where it is likely associated with tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos et al. This species is far more common in the foothills of the Sierra Nevada and Shasta Cascade range in May–June where the primary association in the lower elevations (2000–4000 feet) is with the deciduous black oak (Quercus kelloggii Newb.). At higher elevations A. vernicoccora may switch association to conifers, but we have not seen it outside of the range of the black oak (≤6000 feet).