The title compound, C20H32O2 (systematic name: 3-ethenyl-3,4a,7,7,10a-pentamethyldodecahydro-9H-benzo[f]chromen-9-one), was isolated from Sideritis perfoliata. In the crystal, molecules pack in helical supramolecular chains along the 21 screw axis running parallel to the a axis, bound by C—H...O hydrogen bonds. These chains are efficiently interlocked in the other two unit-cell directions via van der Waals interactions. Hirshfeld surface analysis shows that van der Waals interactions constitute the major contribution to the intermolecular interactions, with H...H contacts accounting for 86.0% of the surface.