Petasides hybridus (butterbur) is a perennial shrub, found throughout Europe as well as parts of Asia and North America, that has been used medicinally for centuries. During the Middle Ages butterbur was used to treat plague and fever; in the 17th century its use was noted in treating cough, asthma, and skin wounds. The plant can grow to a height of three feet and is usually found in wet, marshy ground, in damp forests, and adjacent to rivers or streams. Its downy leaves can attain a diameter of three feet, making it the largest of all indigenous floras, and their unique characteristics are responsible for the plant's botanical and common names. The genus name, Petasites, is derived from the Greek word petasos, which is the felt hat worn by shepherds. The common name of butterbur is attributed to the large leaves being used to wrap butter during warm weather. Other common names include pestwurz (German), blatterdock, bog rhubarb, and butter-dock. Currently, the primary therapeutic uses for butterbur are for prophylactic treatment of migraines, and as an anti-spasmodic agent for chronic cough or asthma. It has also been used successfully in preventing gastric ulcers, and in treating patients with irritable bladder and urinary tract spasms.