One of the many sterile epiphytic lichens from high humidily forest habitats in Atlantic Canada has been identified as belonging to Moelleropsis (Lecanorales). The assignment was made on the basis of the granular, virtually undifferentiated thallus which is remarkably similar to that of the European M. nebulosa (Hoffm.) Gyeln., but pseudofruticose ramifications from the thallus surface and fruiting bodies were not observed. The Canadian Moelleropsis is described as a subspecies of M. nebulosa, namely ssp. frullaniae. The epithet refers to the hepatic Frullania tamarisci ssp. asagrayana which is the preferred substrate of the lichen. The taxonomic difficulties in assessing cell size differences between the symbionts of closely related lichens are outlined.