Our floristic work in British ancient forests resulted in a description of a frequently reported but misidentified species, Coenogonium nimisii. Its thallus is very similar to Porina rosei, but the apothecia and pycnidia correspond with C. luteum. Sterile collections are not easy to distinguish but the new species differs from P. rosei in several microscopic characters of the isidia. Coenogonium nimisii is so far known from bark and epiphytic bryophytes, rarely mossy rocks, in ancient humid forests of Great Britain and Ireland. The genus Coenogonium is poorly represented by molecular data in the GenBank database. Our preliminary results revealed distinct genetic lineages within two traditionally circumscribed species, C. luteum and C. pineti, which may represent cryptic species.
