Resolving the taxonomic challenge of cryptic diversity in the Balkan‐Anatolian <i>Cardamine acris</i> complex using an integrative approach

Abstract Delimiting taxa within recently diversified species complexes that exhibit conflicting genetic, morphological, or cytogenetic patterns is challenging. The Cardamine acris complex, a group of hygrophytic perennials distributed in the montane to (sub)alpine belts of the Balkan Peninsula ( C. acris ) and northwestern Anatolia ( C. anatolica ), exemplifies this complexity. Building on recent phylogenomic evidence of pronounced cryptic diversity, we employed an integrative approach that combined dense geographic sampling, morphometric analyses, flow cytometry, and molecular data to reassess the taxonomic treatment of the complex and reconcile patterns in genetic, phenotypic, and nuclear DNA content variation. Our results confirm the distinctiveness of previously recognized taxa ( C. acris subsp. pindicola , subsp. vardousiae , and C. anatolica ) and demonstrate that the traditional broad circumscription of C. acris subsp. acris is at odds with the observed patterns of variation. We identified three allopatric Balkan lineages and recognize them at the subspecies level, describe two new subspecies, C. acris subsp. dinarica and subsp. grisebachii , and restrict C. acris subsp. acris to the western Balkan region from the Shar Planina to the Gramos Mountains. In this revised concept, the complex comprises two species, C. acris and C. anatolica , with five subspecies recognized within C. acris . Patterns of morphological and nuclear DNA content variation are only partly congruent with phylogenomic relationships, likely reflecting recent Pleistocene diversification, reticulation, and polyploidization events. We propose a progenitor‐derivative speciation scenario for the species pair C. acris and C. anatolica , and support the species‐level treatment for C. anatolica even though it is phylogenetically nested within C. acris . Overall, our study highlights the importance of comprehensive sampling and integrative approaches for resolving taxonomically complex groups and illustrates how diverse evolutionary processes can generate intricate patterns of variation.