What is "heterobasidion"

Heterobasidion is a genus of basidiomycetes in the family Bondarzewiaceae. Species in this genus include forest decay fungi that may be pathogenic and cause tree decline and mortality. The genus can be identified from its shelf-like polyporous fruiting bodies. Mating studies in the late twentieth century and genetic studies in the early twenty-first century have described several new species and replacing some of the original names. As a result, two former Heterobasidion species, H. annosum and H. insulare, have been expanded into species clusters.