Protocatechuic acid can be isolated from the stem bark of Boswellia dalzielii. A?aí oil is rich in protocatechuic acid. Protocatechuic acid also exists in the skins of some strains of onion as an antifungal mechanism, increasing endogenous resistance against smudge fungus. It is also found in Allium cepa. PCA occurs in roselle (Hibiscus sabdariffa) Protocatechuic acid is also found in mushrooms such as Agaricus bisporus or Phellinus linteus. http://www.guidechem.com/cas-99/99-50-3.html
Heartwood is one of the plants that contain protocatechuic acid. It is also well recognized for its activity against leprosy, diabetes, and other skin infections. Heartwood is also useful in diarrhea and hemophilic diseases.