Diffractaic acid is a ò-orcinol depside with the molecular formula C<sub>20</sub>H<sub>22</sub>O<sub>7</sub>, which is produced by lichens. Diffractaic acid has cytotoxic, cytogenetic, oxidative, analgesic and antiviral effects.
The foliose lichen species Punctelia diffractaica is named for the presence of this compound.