The disease-causing agent of Ash dieback in Europe was identified only in 2006. It was first described as a new fungal species, Chalara fraxinea. This is why the disease is still commonly named "Chalara". In 2009, based on morphological and DNA sequence comparisons, C. fraxinea was suggested to be the asexual stage (different stage of same biological species) of the ascomycete Hymenoscyphus albidus. However, in 2010 more detailed molecular investigations led to the conclusion that the disease agent belongs to a biologically different entity than H. albidus, and consequently, the ash dieback pathogen was described as H. pseudoalbidus.