3-Methylorsellinic acid (β-orcinolcarboxylic acid) was originally identified as a degradation product of barbatinic acid in 1928. In 1976, 3-methylorsellinic acid was isolated as a co-metabolite of its dimer, 4-O-demethylbarbatic acid, and asterriquinone from Aspergillus terreus by researchers at Kanazawa University, Japan. 3-Methylorsellinic acid is an important sub-unit of diverse depsides found in lichens. 3-Methylorsellinic acid is a useful standard for dereplication of fungal secondary metabolites.