A Revised Phylogeny of the <i>Mentha spicata</i> Clade Reveals Cryptic Species
2021
Olivier C. G. Heylen | Nicolas Debortoli | Jonathan Marescaux | Jill K. Olofsson
The genus <i>Mentha</i> is taxonomically and phylogenetically challenging due to complex genomes, polyploidization and an extensive historical nomenclature, potentially hiding cryptic taxa. A straightforward interpretation of phylogenetic relationships within the section <i>Mentha</i> is further hindered by dominant but outdated concepts on historically identified hybrid taxa. <i>Mentha spicata</i> is traditionally considered to be of hybrid origin, but the evidence for this is weak. Here, we aim to understand the phylogenetic relationships within the section <i>Mentha</i> using large sample sizes and to revisit the hybrid status and identity of <i>M. spicata</i>. We show that two of three traditional species in the subsection <i>Spicatae</i> are polyphyletic, as is the subsection as a whole, while the real number of cryptic species was underestimated. Compared to previous studies we present a fundamentally different phylogeny, with a basal split between <i>M. spicata</i> s.s. and <i>M. longifolia</i> s.s. Cluster analyses of morphological and genotypic data demonstrate that there is a dissociation between morphologically and genotypically defined groups of samples. We did not find any evidence that <i>M. spicata</i> is of hybrid origin, and we conclude its taxonomic status should be revised. The combination of genetic and phenotypic information is essential when evaluating hyperdiverse taxonomic groups.
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