This fungus is not common, its is found on various broad leaved trees, in particular:
Ash, Robinia, Laburnum, Elm, Plane, Poplar and Beech.
A perennial fruiting fungal bracket with a very hard and woody texture found at the stem base of a tree. When young the fungus is whitish, and turns dark brown/blackish with age. When mature the fungal bracket can be 400 mm across. On the underside of the fungus are its tubes, they are a pale yellowish colour.
A tree which is in the advanced stage of infection is subjected to an intense white rot, which means the wood becomes brittle. Making an infected tree prone to brittle fracture of it’s stem base and roots.