The cap is gray or brownish, 5 to 10 centimetres (2 to 4 inches) in diameter, and has furrows around the edge that duplicate the gill pattern underneath.

The stem surface is covered with a finely powdered bloom (pruinose), especially near the top; faint longitudinal lines may be seen.

[5] The base of the stem is enclosed in a loose, sack-like volva that may discolor grayish or reddish brown.

[7] The spores are roughly spherical, 8–12 μm in diameter, thin-walled, and nonamyloid (that is, not absorbing iodine stain in Melzer's reagent).

[4] The pileipellis (cap cuticle) is composed of filamentous interwoven hyphae, 2–7 μm diameter, gelatinized.

[8] In North America, A. vaginata is considered to be part of a species complex that includes A. constricta, A. pachycolea and A. protecta.