The title compound, C12H14O6, a substituted isophthalic acid monoester which was isolated from the lichen Thamnolia vermicularis var. subuliformis, displays intramolecular carboxyl–methoxy O—H⋯O and hydroxy–carboxyl O—H⋯O hydrogen-bonding interactions. The terminal methyl group of the ethyl ester is disordered over two sets of sites with occupancies of 0.599 (19) and 0.401 (19)
