Polyporic acid is a para-terphenyl benzoquinone compound first identified by German chemist Stahlschmidt from a mycelial culture of the fungus species Hapalopilus nidulans in 1877. This chemical, present at 20–40% of the fresh weight of the fruit bodies, inhibits the enzyme dihydroorotate dehydrogenase. It is found in other mushrooms, but in much lower amounts.