3-Eth-oxy-carbonyl-2-hy-droxy-6-meth-oxy-4-methyl-benzoic acid.

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).