The secret 'walnut defense' | Science Blog:
These laboratory experiments, led by ARS research chemist Russell J. Molyneux of the agency's Western Regional Research Center at Albany, showed that a popularly grown walnut known as Tulare was remarkably resistant to Aspergillus. Molyneux did the work with chemist Noreen E. Mahoney at the Albany laboratory and with University of California, Davis, collaborator Jim McKenna. Davis researchers Charles A. Leslie and Gale H. McGranahan also participated.
Tulare's secret defense? It's gallic acid, found only in the nutmeat's thin skin, or pellicle, according to Molyneux. Tulare walnuts contained one-and-one-half to two times more gallic acid than, for instance, Chico walnuts, the most Aspergillus-susceptible of the walnuts that the researchers tested.
Evolved defenses against a toxic fungus.