Hericium flagellum is a highly host-dependent wood-inhabiting fungus in Europe. Its occurrence is strongly connected to the distribution of silver fir (Abies alba). We analysed available data describing ecological factors, especially habitat, substrate preferences and phenology, which are regarded as drivers of H. flagellum occurrence. We also implemented ecological niche modelling to determine the potential range of the fungus. More than half of H. flagellum records (57%) were found in high conservation value areas, on fallen trunks of silver fir trees. The basidiomata were predominantly recorded between August and late November. Distribution of the tree host, precipitation in the driest month, isothermality and annual mean temperature were the most decisive factors influencing H. flagellum occurrence. We conclude that the disjunctive range at present, the risk of tree host extinction linked to habitat loss, and the limited dispersal of H. flagellum propagules are the main threats to this species.