Butterbur: A waterside plant with purple flowers and large soft leaves in which pats of butter were once wrapped during hot weather in England. The rhizome (root) of butterbur has been used as an herbal remedy for fever, asthma, colds, and urinary complaints and was also thought to be a cardiac "tonic" and a diuretic.

Butterbur holds some promise as a treatment for allergy because it contains petasin, which blocks leukotrienes and inhibits histamine. Histamine plays a major role in many allergic reactions by dilating blood vessels and making vessel walls abnormally permeable. The leukotrienes are substances that mediate inflammation and contribute to the symptoms of hayfever and asthma.

The scientific name of butterbur is Petasites vulgaris or Petasites hybridus.