Mentha canadensis L. (Lamiaceae): a relict amphidiploid from the Lower Tertiary

Two clones of Mentha arvensis L., both with 2 n = 72 from Europe, one with 49.20 ± 2.28% pulegone, another with 57.31 ± 9.41% linalool, were hybridized with M. longifolia (L.) L. from Europe with 2 n = 24 and 51.87 ± 0.50% trans‐piperitone oxide. The F 1 hybrids had essential oils rich in pulegone, isomenthone, menthone, trans‐isopulegone, menthol, neomenthol, 3‐octanol, linalool, cis‐piperitone oxide, trans‐piperitone oxide, carvone, limonene, piperitenone oxide, trans‐carveol, trans‐sabinene hydrate, 3‐octanone, terpinen‐4‐ol, (Z)‐β‐ocimene, geranyl acetate, citronellyl acetate, and/or β‐caryophyllene. Thirty‐nine F 1 hybrids of this cross are similar to 23 clones of M. canadensis L. from North America and Asia with 2 n = 96 when compared by chromosome numbers, morphology, and essential oils. Mentha canadensis is proposed as a relict amphidiploid of the mixed mesophytic flora of the Lower Tertiary.