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

Two clones of Mentha arvensis L., both with 2n = 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 2n = 24 and 51.87 +/- 0.50% trans-piperitone oxide. The F-l hybrids had essential oils rich in pulegone, isomenthone, menthone,l; 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)-beta-ocimene, geranyl acetate, citronellyl acetate, and/or beta-caryophyllene. Thirty-nine F-l hybrids of this cross are similar to 23 clones of M canadensis L. from North America and Asia with 2n = 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.