Is there a need for accepting paraphyletic taxa? A case study in the Sardinian endemic Cymbalaria muelleri (Plantaginaceae)

Evolution does not always result in dichotomous phylogenetic trees. For instance, in anacladogenetic speciation, where a new species originates by budding, the ancestral taxon is often initially paraphyletic. Here we study Cymbalaria muelleri (Plantaginaceae), a chasmophytic species endemic to Sardinia, a major island in the Mediterranean Basin. Its distribution range is divided into two well-delimited geographical groups with some morphological differences. Using a combination of morphology, molecular data (amplified fragment length polymorphism fingerprinting) and relative genome size, we found that the two geographical groups should be considered two separate taxa, which split through anacladogenesis. Accordingly, we formally describe the new paraphyletic subspecies C. muelleri subsp. villosa as the ancestor, from which C. muelleri subsp. muelleri originated by budding. Morphological analyses support the differentiation of the two subspecies, and there are strong diagnostic characters to differentiate them. In addition to morphology and genetics, slightly divergent habitat preferences and the disjunct distribution of the two subspecies also support the recognition of two taxa. Genome size data obtained for the two subspecies are consistent with the previously established hexaploidy of C. muelleri.