We have very recently characterized four isomeric terpene–coumarin derivatives with the formula C₂₀H₂₂O₅ from the aerial parts of Ethulia conyzoides L. [1]. This report deals with the isolation and structural elucidation of another major compound, C₂₀H₂₄O₆, representing a hydrated derivative of the above isomers. Its ¹H NMR (see Table 1) and MS data clearly establish structure 1. The stereochemistry at C-5' and C-6', however, has not been determined. The proposed structure was also confirmed through treatment with periodate to afford the lactone 2 previously obtained from two of the isomers after similar treatment [1, 2].