Sample selection and herbarium label interpretations
A total of 155 herbarium specimens of Mentha subgen.Mentha were obtained from the herbaria at Lund University, Sweden (LD), Uppsala University, Sweden (UPS), and Oskarshamn, Sweden (OHN); Table S1. Specimens were selected based on the plant identification by the collector(s) and/or subsequent re-identifications by botanists, with the aim to include the taxa, M. longifolia , M. suaveolens ,M. spicata , and the hybrid M. × rotundifolia(M. longifolia × suaveolens ). However, many specimens were re-identified based on the result of our morphometric analyses (see below). From here on, the taxon names M. longifolia (L.) L.,M. suaveolens Ehrh., M. spicata L. and M. capensisThunb. (and their hybrids) are used to denote those groups of specimens identified by the morphometric analyses that most closely correspond to the morphological descriptions of these species in standard floras (Stace, 1993; Tutin, 2010). However, it should be stressed that these morphologically defined groups may not exactly correspond to the biological species that previous authors have referred to by these names, nor to their nomenclatural types. All specimens were morphologically evaluated and a subset of 93 samples were whole genome sequenced.