Discina gigas

Discina gigas, commonly known as the snow mushroom, snowbank false morel, walnut, giants false morel,  snow morel, snow false morel, calf brain, or bull nose, is a species of fungus and a member of the Ascomycota found in Europe. It is referred to as one of the false morels, due to its similar appearance and occurrence in the spring and early summer in similar habitats to true morels (Morchella ssp.).

Taxonomy
The species was first described scientifically by Julius Vincenz von Krombholz as Helvella gigas.

Similar species
Hence its common name, Discina gigas resembles true morels, Morchella ssp. D. gigas also resembles toxic species of the genus Gyromitra.

A very similar and directly related species, D. montana, occurs in North America; it apparently has larger spores than D. gigas. While both species are reportedly edible in small amounts if thoroughly cooked, eating is not recommended due to their similarity to more toxic species of mushrooms.

Toxicity
It contains small quantities of hydrazines; its content in gyromitrin was scientifically assessed by Viernstein et al. [Botanical identification 1980] and resulted of about 1mg per kg of fresh mushroom (roughly 1,500-fold less compared to that of Gyromitra esculenta). Though no casualties have been ascribed to its consumption, parboiling is still highly recommended. Some guides have listed it as being edible if properly prepared. However, consumption is not recommended due to variability and similarity to other more toxic species of the genus Gyromitra.

This fungus has been banned for sale in France since 1991 due to potential toxicity, the effects of which would cause a fairly rare fatal neurodegenerative disease, amyotrophic lateral sclerosis (ALS).