Phenolic acids as chemotaxonomic markers able to differentiate the Euphrasia species

The objective of this study was to get the answer on the question, which phenolic compounds may serve as chemical markers in taxonomy of Euphrasia spp. (E. nemorosa, E. rostkoviana, E. stricta) collected from the wild. Moreover, it is still unknown how and which environmental parameters can impact on the quantity of polyphenols, flavonoids and phenolic acids. To the authors' knowledge, this is the first study that analyses such a broad spectrum of phenolic compounds in the genus Euphrasia and takes into account the habitat conditions of their synthesis. The species of Euphrasia differ significantly in the content of phenolic compounds. Euphrasia rostkoviana has the highest total content of polyphenols and flavonoids. Euphrasia stricta contains the largest amounts of phenolic acids, such as 5-O-caffeoylquinic, p-coumaric, protocatechuic and salicylic acid. It has been evidenced that the content of metabolites in the Euphrasia herb depends on a number of habitat parameters. The increased content of phenolic acids in E. stricta can be attributed to the fact that this species occupies drier habitats, with lower content of nitrogen and organic carbon compared to E. nemorosa and E. rostkoviana. The compounds that can be considered as chemotaxonomic markers are salicylic and protocatechuic acid for E. stricta, 5-O-caffeoylquinic acid for E. rostkoviana and ferulic acid for E. nemorosa. These findings provide theoretical and empirical basis for a chemotaxonomic classification of those species, which taken together with morphological characteristics should prevent misidentification.