The current interpretation of two common European species, Mordellistena minima Costa, 1854 and M. pseudorhenana Ermisch, 1977, is based on misidentification. The confusion regarding the identity of the species is fixed based on the revised type material. Here, the species are redescribed, and diagnostic characters are provided. Mordellistena pseudorhenana is revalidated. Mordellistena emeryi Schilsky, 1895 is recognised as a new synonym of M. minima. Mordellistena sajoi Ermisch, 1977 is recognised as a new synonym of M. pseudorhenana. Lectotype and paralectotypes of M. emeryi are designated. Mordellistena pseudorhenana is reported for the first time from Bosnia and Herzegovina, Slovenia, and Switzerland. Two morphotypes of M. pseudorhenana differing in size and shape of the parameres are recognised. Morphological differences are quantified and displayed using principal component analysis. In addition, DNA barcodes have been used for the first time in family Mordellidae to examine the divergences between the species and to interpret the morphological variability observed in M. pseudorhenana. Low genetic divergences did not provide the evidence for considering the morphotypes as separate species. The discrepancy between the morphological and molecular evidence raises questions about the efficiency of the CO1 gene for Mordellidae identification and the stability of morphological traits conventionally used for species separation.