Sesquiterpene lactones (SLs) are a class of sesquiterpenoids that contain a lactone ring. They are most often found in plants of the family Asteraceae (daisies, asters). Other plant families with SLs are Umbelliferae (celery, parsley, carrots) and Magnoliaceae (magnolias). A collection of colorless, lipophilic solids, SLs are a rich source of drugs.[1] They can be allergenic and toxic in grazing livestock[2] causing severe neurological problems in horses. Some are also found in corals of the order Alcyonacea.