Hymenochaete ametzii sp. nov. (Hymenochaetales, Basidiomycota), an endangered bark-dwelling species inhabiting old Quercus pyrenaica trees from the Iberian Peninsula

Bark-dwelling fungi represent a group of ecologically highly specialized organisms. This study deals with an undescribed species of Hymenochaete characterized by specifically inhabiting the bark of Pyrenean oak (Quercus pyrenaica), and producing effuse-reflexed basidiomata and mainly globose to subglobose basidiospores. Maximum Likelihood and Bayesian analyses of the nuclear ITS-LSU regions revealed that the sequences of H. ametzii form a monophyletic group with a low intraspecific variation and substantially different from closest taxa, further supporting its recognition as a species. The seven localities H. ametzii is known from are old forests with a long ecological continuity, containing large old Q. pyrenaica trees, and are located in the supramediterranean belt of the Mediterranean biogeographical region. Based on habitat availability and field counts of colonized trees, the global population of H. ametzii is estimated at 8,670 mature individuals. Considering that the traditional use of old Q. pyrenaica stands ceased several decades ago in the Iberian Peninsula, with a consequent decline in habitat quality and availability, it is concluded that H. ametzii is Endangered (EN) according to the IUCN criteria.