Biscogniauxia nummularia is a plant pathogen in the family Graphostromataceae, known as the beech tarcrust.

[1] The specific epithet is derived from the Latin "nummus" meaning a coin, referring to the often rounded and coin-like encrustations.

The fruit body forms a thick and shiny black crust, on beech (Fagus) bark and is found at all times of the year.

Biscogniauxia nummularia is a common pathogen specific for Beech trees, and has been recorded throughout Europe and Russia.

[2] The decline of European beech (Fagus sylvatica) in Sicily and Calabria (Italy) has been linked to B. nummularia and experiments have suggested that this ascomycete plays a primary pathogenic role under certain environmental conditions.