Plants of Senecio othonniformis Fourcade afforded the alkaloids, bisline, C₁₈H₂₇NO₆, and its acetate, isoline, C₂₀H₂₉NO₇. Hydrolysis of isoline gave acetic acid, retronecine, and a new acid, isolinecic acid, C₁₀H₁₈O₆. N.m.r. and mass spectral data and degradation studies indicate that isolinecic acid is 2,5-dihydroxy-3-methylheptane-2,5-dicarboxylic acid or its 2,4-dihydroxy-isomer.