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.

[1][2] This chemical, present at 20–40% of the fresh weight of the fruit bodies,[3] inhibits the enzyme dihydroorotate dehydrogenase.

[4] In animal studies, consumption of polyporic acid caused reduced locomotor activity, depressed visual placing response, hepatorenal failure, metabolic acidosis, hypokalaemia, and hypocalcaemia.

[4] Because these effects are similar to those observed in individuals poisoned by H. nidulans, polyporic acid is thought to be the primary toxin in H.

[6] It has been shown to be an intermediate in the biosynthesis of allantofuranone, a gamma-lactone antibiotic from the fungus Allantophomopsis lycopodina.