Cabergoline is a synthetic derivative of ergotine, a natural alkaloid produced by the fungus Claviceps purpurea, otherwise known as Ergot. There Claviceps purpurea it is an ascomycete that infests grasses, especially rye.
Cabergoline - Chemical Structure
When rye is infested with this parasite it is called ergot due to the sclerotia in the shape of small horns that this organism forms on the plant.