White trunk rot fungus (Phellinus igniarius) fruiting body, on the trunk of a tree. This hard, hoof-shaped fruiting body (known as a conk") holds the spores and is produced during reproduction. The white trunk rot fungus is a serious pathogen of hardwood trees, entering through branch stubs and feeding on living wood. The interior of the trunk becomes soft as it decays and the tree may die as a result."