BRIEF DESCRIPTION: Fruiting bodies of A. atrofusca are medium-sized. The cap is 60 - 100 mm wide, obtusely umbonate, dark brown, often with a darker colored ring-like zone at the inner end of the marginal striations, and glabrous. The cap's margin is tuberculate-striate (20% - 30% of radius) and non-appendiculate; and the cap's context is white to dirty white.

The gills are whitish to greyish, with brown to brownish edges; and the short gills are truncate.

The exannulate stem is 120 - 150 x 8 - 13 mm, subcylindric or slightly attenuate upwards, fistulose, and with its surface densely covered with dark brown, furfuraceous squamules; the stipe lacks a basal bulb. At the stipe's base, the volva is saccate, with its outer surface whitish to brownish and decorated with brownish spots, and with its inner surface brownish.

The spores measure (9.5-) 11.0 - 14.5 (-15.0) x (8.5-) 11.0 - 14.5 (-15.0) µm and are globose to subglobose and inamyloid. Clamps are absent from the bases of basidia.

Amanita atrofusca was described from China, and it is not uncommon in subalpine to alpine regions of southwestern China. -- Zhu L. Yang

For a provisional list or most similar taxa see A. vaginata var. alba Gillet.
-- R. E. Tulloss