Cap 5.5-10.0 cm broad, convex, expanding to plano-convex, in age sometimes centrally depressed with a low umbo; margin at first decurved, plane to elevated at maturity, tuberculate-striate, the striations up to 1.2 cm long; surface when young partially covered with a membranous, white universal veil patch or patches which may discolor pale ochraceous-brown; at maturity the veil patches typically disappearing, the cap then grey to grey-brown, sticky when moist, glabrous except for the margin; context white to pale grey, firm, up to 1 cm thick; odor and taste mild.
Gills narrowly attached to free, close, thin, up to 1 cm broad, white to pallid, the edges minutely fringed, greyish near the margin in some specimens, lamellulae up to 5-seried.
Stipe 6-13 cm long, 1.2-2.0 cm thick, more or less equal, not bulbous, stuffed to hollow; surface of apex pruinose, the ornamentation often arranged in faint grey longitudinal lines over a pallid background, elsewhere grey-brown, squamulose, more coarsely so near the base; universal veil white, membranous, saccate, sometimes discoloring like the cap patches, attached near the stipe base, flaring gradually, not abruptly, from the volva base; partial veil absent.
Spores 8.0-11.5 x 7.5-10 µm, subglobose to globose, smooth, thin-walled, hilar appendage distinct, contents granular with one to several guttules, inamyloid; spore print white.
Solitary to scattered in mixed hardwood/conifer woods; fruiting from late fall to mid-winter.
Edible, but not special; see "Comments."
Amanita vaginata is part of a complex of grey to brown-capped Amanitas that are found in the coastal forests of California. Besides Amanita vaginata, the group includes Amanita constricta, Amanita pachycolea, and Amanita protecta. All have striate caps, lack a partial veil/annulus, and have inamyloid spores. Smallest of the group is Amanita vaginata which is characterized by a greyish cap, evanescent, white, universal veil cap patches that discolor pale ochre, and a volva that flares gradually from the stipe. Amanita constricta differs slightly in cap color, more brown to grey-brown, with universal veil cap patches that typically discolor rust-brown; more significantly, the volva of Amanita constricta, as the species name suggests, is appressed tightly to the stipe, with only the margin flaring. Amanita pachycolea is a large, robust species with a conspicuously striate, brown cap. An important fieldmark is a universal veil which is thicker than either of the above species, flaring from the base, and discoloring rust-brown. Finally Amanita protecta, differs from all of the above in having a cottony-membranous, sheathing, not flaring universal veil that at maturity crumbles leaving scaly patches on the lower portion of the stipe and often a short collar-like volva at the base. Although Amanita is known for its toxic, sometimes lethal species, members of the A. vaginata complex in California (except for A. protecta for which there is little record) are thought to be edible. None, however, are generally considered "choice," and thus are seldom eaten. As is always the case with Amanita species, only the most experienced collectors should consider them for the table.