Hypoxylon is a genus of Ascomycetes commonly found on dead wood, and usually one of the earliest species to colonise dead wood. A common European species is Hypoxylon fragiforme which is particular common on dead trunks of beech. Based on morphological studies and gene sequence analyses, 27 species formerly assigned to Hypoxylon sect. Annulata were reassigned to a new genus called Annulohypoxylon in 2005.