BRIEF DESCRIPTION:

The cap of Amanita abrupta is 30 - 90 mm wide, white, sometimes with brick colored stains, subglobose to hemispherical at first, then broadly subcampanulate to convex, becoming planoconvex or planar, eventually with depressed disc, shiny when dry; context white, unchanging when cut or bruised, 4 - 7 mm thick over stipe; the margin is nonstriate (except possibly in age), decurved, appendiculate at first with fibrillose white narrow nearly continuous band descending from pileus margin. The volva on the cap is present as acutely pointed pyramidal to subconic warts (1 - 2 mm high and 1 - 2 mm wide at base) over much of pileus and finer scales near margin, white, sometimes becoming tannish with age, densely distributed, easily removed.

The gills of A. abrupta are narrowly adnate to free, with a decurrent tooth on the stipe apex or with a decurrent line on the upper stipe, close to subdistant, white to cream to white with pale ochraceous or orangish tint in mass, white in side view, unchanging when cut or bruised, 5 - 8.5 mm broad, broadest toward pileus margin, with edges finely fibriate and yellowing slightly with age; the short gills are attenuate.

The stipe is 70 - 81 × 6 - 10 mm, white, faintly browning from handling, narrowing upward, flaring at apex, often pubescent above annulus, fibrillose below, sometimes flocculose or tomentose on lower portion above the bulb.  The bulb 14 - 30 × 14 - 33 mm, abrupt, subnapiform or rounded or somewhat flattened below, occasionally with some longitudinal splitting, with concentric low ridges on upper flat surface, with several to many white mycelical threads at very base. The context of the stipe is white, unchanging when cut or bruised or yellowing in tissue of central cylinder, usually solid or firmly stuffed, with central cylinder 1.5 - 3 mm wide and only notable when the tissue is watersoaked. The annulus is subapical to superior, white, sometimes with yellow stains, membranous, skirt-like, pendant, rather thick, with thickened margin, striate above, felted underneath, often having underside connected to lower stipe surface by numerous white fibrils; volva sometimes appearing as scattered small floccose white warts easily missed during collecting and left in substrate or as a patch on lower stipe and/or as thin ridges and rings on top and upper part of sides of bulb.

Odor of this species is in the "decaying protein" group.  The taste is not recorded.

The spores are (6.1-) 7.2 - 9.0 (-10.7) × (4.8-) 5.9 - 7.5 (-9.2) µm and are subglobose to broadly ellipsoid to ellipsoid and amyloid. Clamps are present on bases of basidia.

The species occurs in deciduous, coniferous, and mixed forests with beech, birch, fir, hemlock (Tsuga), oak, pine, and poplar.

The range of A. abrupta extends from Quebec, Canada to Georgia and Texas, U.S.A. and westward to the eastern limit of treeless prairie.

The present species is a member of Bas' stirps Microlepis. A very similar, but distinct, species in Japan is A. sphaerobulbosa Hongo. -- R. E. Tulloss