Abstract <p>A number of secondary phenolic metabolites identified with previously characterized substances usnic acid (<b>1</b>), rhein (<b>2</b>), and chrysophanol (<b>3</b>) are isolated for the first time from the <i>Xanthoria&#xa0;elegans</i> lichen collected in the Namangan region of Uzbekistan (Pop district, Chadak village). The obtained usnic acid has a different melting point than that reported earlier in the literature; so the substance was studied by XRD. The difference from the known data is that the isolated usnic acid crystallizes in the <i>P</i>2₁/<i>c</i> space group, meaning that both (<i>S</i>) and (<i>R</i>)-enantiomers participate in the crystallization process. The presence of a migrating hydrogen atom established experimentally by the difference EP synthesis method and the analysis of valence bond lengths show that the usnic acid molecule can exist in the crystal in the form of two equilibrium keto and enol tautomers. An <i>in vitro</i> study on four cancer cell lines reveals that the extract of <i>X. elegans</i> exhibits slight cytotoxicity against the CCRF-CEM T-lymphoblastic leukemia cell line.</p>