Biscogniauxia nummularia is a plant pathogen in the Xylariaceae

Xylariaceae

The Xylariaceae are a family of mostly small ascomycetous fungi. It is one of the most commonly encountered groups of ascomycetes and is found throughout the temperate and tropical regions of the world. They are typically found on wood, seeds, fruits, or plant leaves, some even associated with...

 family, known as the Beech Tarcrust. The Latin 'nummus

Nummus

Nummus , plural nummi is a Latin term meaning "coin", but used technically for a range of low-value copper coins issued by the Roman and Byzantine empires during late Antiquity....

' meaning a coin

Coin

A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....

, applied as the encrustations are often rounded and coin-like.

Views of the Beech Tarcrust

The fruiting body forms a thick and shiny black crust, on Beech (Fagus) bark and is found at all times of the year. It is not edible. Young specimens are covered by a light brown outer layer. The spores are black to dark brown. B. nummularia is a common fungus specific for Fagus, and has been recorded from all parts of Europe and Russia, following the extensive distribution of its host tree.

B. nummularia as a primary pathogen

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. It typically causes strip-canker and general wood decay.