Morphological and molecular data support the distinction of four sorediate corticolous <i>Candelariella</i> species in Europe

Abstract Corticolous sorediate Candelariella represent, at least in Europe, a widespread group of species, often predominant in epiphytic communities. Many specimens are challenging to identify since apothecia are generally lacking and names have been frequently misapplied in the past. Here, we studied the morphology and molecular data (ITS nrDNA sequences) of corticolous sorediate Candelariella specimens, with the aim of determining how many species occur in Europe and which names should be applied. We distinguish worldwide five taxa from this group that are widespread and currently well supported by both morphological and molecular data. These include three 8-spored species ( Candelariella reflexa, C. rubrisoli and C. xanthostigmoides ) and two polyspored species ( C. efflorescens and Candelariella pulchella sp. nov., the latter characterized by coarser soredia, larger apothecia with a persistent proper margin and broader paraphyses tips). Four of these species (all except C. xanthostigmoides ) occur in Europe. European specimens previously identified as C. xanthostigmoides belong to C. rubrisoli. Candelariella makarevichiae and C. subsquamulosa are considered synonyms of C. xanthostigmoides. Candelariella sorediosa , C. flavosorediata and C. magellanica (the latter two not reported from Europe) remain poorly known species for which molecular data is currently lacking and they require further study. Full descriptions and a key to the species discussed are provided.