Lecidea swartzioidea is rather close to Lecidea lapicida, differeing in blackish brown (instead of unpigmented or medium brown) hypothecia and characterized by a well developed epilithic thallus and a K+ red reaction of the medulla, caused by norstictic acid.  Its circumspection still is somewhat critical, because its variability within the Lecidea lapicida group is not fully understood.  Lecidea lygomma Nyl., a widespread, mainly Subantarctic species, differs in always having a negative I- reaction of the medulla.  For arctic Russia, this species is mentioned only for Novaya Zemlya (Andreev et al. 1996; Lynge 1928).