Phytochemical Diversity and Genetic Characterization of Mountain Tea (Sideritis sect. Empedoclia) from Greece

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Members of Sideritis sect. Empedoclia (Lamiaceae), known as ‘mountain tea’, are widely used medicinal plants. Their taxonomic classification is complex due to frequent hybridization and subtle morphological distinctions. This study examines 12 populations of eight native Sideritis taxa from Greece: S. clandestina subsp. clandestina, S. clandestina subsp. peloponnesiaca, S. euboea, S. raeseri subsp. raeseri, S. raeseri subsp. attica, S. scardica, S. sipylea, and S. syriaca subsp. syriaca. The objectives were to (1) monitor non-polar secondary metabolites (mainly terpenoids) using gas chromatography; (2) shed light on their phylogenetic relationships; (3) evaluate the correlation between genetic and chemical data. Diterpenes, particularly sideridiol, siderol, 7-epicandicandiol, and ent-3α,18-dihydroxy-kaur-16-ene, were the most abundant chemical compounds. Categorical Principal Component Analysis revealed that S. raeseri subsp. attica is chemically distinct, while the rest are grouped into two clusters: one comprising S. clandestina and S. sipylea, and the other including all the rest. Genetic analysis based on chloroplast DNA (matK, psbA-trnH, trnL-F), showed that S. sipylea and S. syriaca subsp. syriaca were the most phylogenetically distant groups. Our study enhances the understanding of Sideritis chemovariability and phylogeny, supporting also taxonomic, authentication, and breeding efforts.