Common Name: Western Grisette
Cap 8-18 cm broad, rounded at first, then convex, finally plane and slightly umbonate at maturity; surface viscid when moist; color dark brown, fading to light brown in age, occasionally with a remnant of universal veil tissue; margin conspicuously and deeply striate.
Gills adnexed to free, close white with brown edges.
Stipe 10-25 cm long, 1-3 cm thick, equal to narrower at the apex; pallid, covered with fine brown scales. Annulus absent. Universal veil forming a thick, membranous sac-like volva, sometimes developing rusty stains.
Spores 11.5-14.0 x 10-12 µm, smooth, nonamyloid, globose to subglobose. Spore print white.
Found commonly from mid-fall to mid-winter in mixed hardwood coniferous forest.
Edible but not choice.
Amanita pachycolea can be recognized by its large size, dark brown, deeply striate cap, absence of a ring, and well developed thick white, membranous volva. Its cousin, Amanita vaginata, is similar but smaller, has a cap which is not nearly so deeply striate, and is grayish rather than brown. Both species, however, can develop rusty stains on the volva.