BRIEF DESCRIPTION: The following is based on the very limited original description of this species.

The cap of A. ushuaiensis is 70 - 110 mm wide, olive-brown to gray-brown hemispheric at first, becoming convex to planar, shiny, often with a silvery sheen, sometimes becoming strongly areolate.  The flesh is firm.  The volva is present as thick, pale brown patches.

The gills are free to narrowly adnate, moderately distant, pallid cream, with a thickened edge.  The short gills are truncate to rounded truncate, of diverse lengths, and common.

The stem is 70 - 120 × 10 - 45 mm, narrowing upward, entirely pale grayish white, more or less club-shaped at maturity, with longitudinal grooves.  The ring is weak and disappearing.  The bulb is thick and prominent in young material, often slightly tapered, deeply buried in substrate, sometimes splitting, and orangish-brown or dunnish orange or pale dun-colored.  The flesh is white and rather firm.  The volva is not evident in mature material.

According to Raithelhuber (1980, Metrodiana 9) the spores measure 8 - 11 × 5 - 6.5 (-7) µm and are probably predominantly ellipsoid to elongate and are inamyloid.  Clamps are probably present at bases of basidia.

Amanita ushuaiensis occurs infrequently among mosses near Nothofagus pumilio.