Amanita nivalis  

A white to greyish to pale grey-buff mushroom. Pileus 4-8 cm diam., rounded to broadly umbonate, smooth or with a few remnants of white veil on top, with marginal striations extending to ~ 1/3 the cap radius. Stipe slender, typically lacking a ring, (sometimes with an ephemeral ring), cylindrical or slightly swollen downwards, often rather short, white to slightly greyish-buff. Gills white to pale cream. Volva saccate, partly membranous, usually adnate to the stem at the base, flared above into lobes, white but staining ochre. Basidiospores (8.2-) 10.0 - 13.5 (-21) × (7.1-) 8.8 - 12.0 (-19.5) µm, globose to subglobose (occasionally broadly ellipsoidal, rarely ellipsoidal or elongate), inamyloid, without clamps at base of basidia.

Map of known distribution in Great Britain and Ireland.