Abstract
This paper presents a comprehensive study of the underground organs of Achillea millefolium L. using gas chromatography–mass spectrometry (GC–MS), infrared (IR) spectroscopy, and biological tests. The GC–MS results show that the chemical composition of the ethanol extract includes aliphatic acids and their esters, phenolic compounds, flavonoids, and carbohydrates. The main components are 1,3-dihydroxyacetone, octanoic acid, ethyl ester of hexadecanoic acid, eupatilin, and jaceosidin. The IR spectra confirm the presence of aliphatic, carbonyl, and phenolic functional groups characteristic of lipophilic and polar metabolites. The extract exhibited moderate antimicrobial activity against Staphylococcus aureus and Bacillus subtilis, which is associated with the presence of phenolic and flavonoid compounds, as well as moderate cytotoxicity in the Artemia salina test (LD 50 ≈ 82 μg/mL). The results indicate that the underground organs of A. millefolium accumulate lipophilic and phenolic metabolites that determine the antimicrobial and cytotoxic activities of the plant. These findings expand our understanding of the metabolism of common yarrow and confirm the potential of its roots as a source of natural biologically active substances.