Orsellinic acid is a common salicylic acid unit in the biosynthesis of secondary metabolites in actinomycetes, fungi, and lichens, formally isolated from Chaetomium cochliodes in 1959. Orsellinic acid is a key biosynthetic intermediate of many depside metabolites in lichen and fungi. Orsellinic acid is also an important polar co-metabolite present in many fungi, notably Trichomonacea, however, its contribution to overall bioactivity is not well understood. Orsellinic acid is a useful standard for bioassay and analytical techniques for dereplication of common cometabolites.