Riddelliine is a chemical compound classified as a pyrrolizidine alkaloid. It was first isolated from Senecio riddellii and is also found in a variety of medicinal plants including Jacobaea vulgaris, ragwort

Ragwort

Ragwort is a very common wild flower in the family Asteraceae that is native to northern Eurasia, usually in dry, open places, and has also been widely distributed as a weed elsewhere....

, groundsel

Groundsel

Senecio vulgaris, often known by the common name Common groundsel, a humble in appearance member of the Asteraceae family and Senecio genus, is a tenacious deciduous annual whose presence now encompasses the globe in a wide area of easy to somewhat difficult growing conditions.The discussion of...

, and others plants in the genus Senecio

Senecio

Senecio is a genus of the daisy family that includes ragworts and groundsels. The flower heads are normally rayed, completely yellow, and the heads are borne in branched clusters...

(daisies).

Riddelliine can be found as a contaminant in foods such as meat, grains, seeds, milk, herbal tea, and honey.

Riddelliine is suspected to be a carcinogen. It is listed as an IARC Group 2B carcinogen and listed by the National Toxicology Program

National Toxicology Program

The National Toxicology Program is an inter-agency program run by the United States Department of Health and Human Services to coordinate, evaluate, and report on toxicology within public agencies....

in its Report on Carcinogens which lists chemicals "known or reasonably anticipated to cause cancer in humans".