Morphological and molecular evidence supports the species status of the Italian endemic Coenagrion castellani Roberts, 1948 (Coenagrionidae)

Coenagrion castellani Roberts, 1948 was described from Italy as a distinct species almost 75 years ago but has generally not been recognised or was treated as a subspecies of C. mercuriale (Charpentier, 1840). Populations south of the Alps were recently shown to be completely isolated genetically from those in North Africa and elsewhere in Europe. As markings and male appendages also allow for easy separation in the field, C. castellani is best treated as a good species, the 146th odonate species known from Europe and the second one that is endemic to Italy. Its identification and occurrence are reviewed. North African populations are distinct genetically too, but not in morphology. Whether these should be treated as a distinct taxon, e.g. as the subspecies C. mercuriale hermeticum (Selys, 1872), requires further research.