Cardamine rivularis Schur is not the same as Cardamine rivularis auct. non Schur and why does it matter in the genomic era: Resolving the long-standing taxonomic confusion
Correct taxonomic treatment and classification is essential for advanced genomic research, but not always straightforward. Here, we address the long-standing taxonomic confusion regarding the names Cardamine rivularis Schur and C. rivularis auct. non Schur, referring to different entities involved in allopolyploidization events, which is becoming critical due to the increasing number of studies investigating details of polyploid evolution. A number of studies starting from the 1970s up to the present misclassified the parental species of the Alpine neopolyploids C. insueta and C. schulzii, disregarding morphological evidence that was later confirmed by genetic divergence. This prompted us to search for an appropriate taxonomic solution, which remained problematic over the last decades. Here, we apply genome-wide polymorphism screening using whole-genome resequencing and ddRADseq, as well as morphometrics to support C. rivularis Schur and C. rivularis auct. non Schur as separate species and, in particular, to distinguish C. rivularis auct. non Schur from the widespread and polymorphic C. pratensis s.str. The latter two entities are shown here to be genetically distinct, despite the evidence of introgression events, but exhibit only subtle morphological differentiation, suggesting cryptic speciation. The Alpine populations hitherto provisionally assigned to C. rivularis auct. non Schur are described here as the new species C. pseudorivularis Landolt ex Marhold &amp; Lihova. We emphasize that this species, not C. rivularis, was involved in the polyploidization events in the Alps that attracted the attention of many researchers, and appeal for the correct taxonomic classification, using the name C. pseudorivularis. To say in one go, populations of C. rivularis Schur from the Rhodope mountains in Bulgaria also produce allotriploids, which should not be confused with the well-studied triploid C. insueta in the Alps.