What carcinogenic toxin is found in bracken fern?

What carcinogenic toxin is found in bracken fern? The answer is ptaquiloside.

Ptaquiloside is a norsesquiterpene glucoside produced by bracken ferns, especially Pteridium aquilinum. It is regarded as the principal carcinogenic compound responsible for many of bracken’s toxic effects. The compound was first isolated and characterized in 1983.

Under physiological conditions, ptaquiloside can release glucose and form a highly reactive intermediate called ptaquiledienone. This intermediate alkylates biological molecules, including DNA bases, helping explain its mutagenic and carcinogenic activity. Exposure has been associated particularly with gastrointestinal cancers in studies of animals and human populations.

Bracken toxicity is not limited to people eating the fern. Ptaquiloside can leach into soil and water and has been detected in milk and meat from livestock that consumed bracken. In animals, bracken poisoning can cause bone-marrow suppression, bleeding disorders, blindness, and tumors. Phoratoxin, strychnine, and grayanotoxin are toxins from other plants or organisms, not the canonical bracken answer.