A chemotaxonomic investigation of volatile constituents in Stachys subsect. Swainsonianeae (Labiatae).

The composition of the previously unknown essential oils of Stachys subsect. Swainsonianeae (Labiatae) are investigated by GC-MS analyses. The group includes the taxa Stachys ionica, St. spruneri, St. swainsonii ssp. swainsonii, St. swainsonii ssp. argolica, St. swainsonii ssp. melangavica and St. swainsonii ssp. scyronica, all endemic to Greece. Eighteen populations were analyzed, and more than two hundred components were identified. Statistical analyses of oil components separated St. ionica, due to its high amount of (E)-nerolidol, high amount of alpha-cadinol and low amount of (+)-(E)-caryophyllene. The rest of the taxa forms a coherent group where (+)-(E)-caryophyllene, delta-cadinene and partly beta-elemene, (+)-caryophyllene oxide and (+)-limonene predominate but each of them never exceeds 20% of the total. Essential oil composition reflects current taxonomy and phytogeography of the group with a somewhat isolated position for St. ionica. Similarities in morphology and essential oil composition of the St. swainsonii group and St. spruneri may be the result of extensive gene flow in the past. Evidence from volatile oil compounds that may attribute to St. swainsonii ssp. melangavica a hybrid origin from crosses between St. spruneri and St. swainsonii ssp. swainsonii/scyronica group is scarce.