Studies in Perenniporia: Polyporus unitus, Boletus medulla-panis, and the nomenclature of Perenniporia, Poria, and Physisporus, with a note on the European Perenniporia taxa with a resupinate basidiome

The status and identities of Polyporus unitus, type of Perenniporia Murrill, of Boletus medulla-panis, their supposed synonymy, and the nomenclatural status of Perenniporia, Poria, and Physisporus are discussed. It is demonstrated, based on the study of its type, that Pol. unitus is not a synonym of B. medulla-panis even in the historically wider context than that recognised here. Although not precisely identifiable, the type of Pol. unitus does not belong to Perenniporia in its current sense, which is based on B. medulla-panis. Poria Pers. and Physisporus Chevall. are discussed as possible generic names for B. medulla-panis and related taxa. However, in view of the need for nomenclatural stability, it is proposed to maintain Perenniporia as currently accepted, with B. medulla-panis as conserved type. This name is epitypified and Perenniporia medulla-panis redefined. Based on a study of European specimens, two species are recognized within the historical circumscription of P. medulla-panis, Perenniporia meridionalis being described as new. Both species are compared with other European taxa with resupinate basidiomes and a key to all these taxa is presented.