Aims: For effective conservation management of endangered taxa, it is important to define operational units for conservation. In the absence of detailed genetic analyses, morphology-based taxonomy is often used as a surrogate. The Apollo butterfly, Parnassius apollo, is one of the most endangered butterfly species in Europe, considered as a flagship species, with 26 subspecies rank taxa described from the Carpatho-Pannonian region. The subspecific level taxonomy of the species in the region is typically based on old, one-by-one descriptions that are not necessarily comply with today’s taxonomical standards. We aimed to reveal the number of morphologically distinguishable groups among the putative subspecies by applying modern morphometrics.

Location: Carpatho-Pannonian region (Central Europe).

Methods: Landmark-based geometric morphometry analysis on the forewing shape of 949 male and 477 female specimens from 20 Carpatho-Pannonian P. apollo subspecies (both extant and potentially extinct) and an outgroup subspecies using collection material.

Results: We did not support the validity of the 20 subspecies: there was a single division between the Eastern Carpathian populations (described as two subspecies: P. a. transsylvanicus and P. a. rosenius) and the rest of the populations (including the outgroup from the Swiss Alps).

Conclusions: Since P. apollo was not observed in the Eastern Carpathians in the last two decades, and the currently known extant populations in the Carpatho-Pannonian region are all located in the Northern Carpathians, there is a single conservation unit in the region. We suggest that (i) extensive monitoring is needed to reveal whether the unique Eastern Carpathian populations have really gone extinct and (ii) more taxonomical/phylogenetic studies on Central European P. apollo are needed for establishing the taxonomy of the species and efficient conservation strategies. We emphasize that modern integrative taxonomy is not only important for clarifying taxonomical issues, but also for providing basis for sound conservation management.