Petasites is the scientific genus name for several species of flowering plants native to Europe and northern Asia. The plants grow as wildflowers in areas with wet soil, and some varieties are domesticated in flower gardens. Some species of Petasites also have medicinal uses.
The commonly cultivated Petasites japonicus is usually called Japanese butterbur or sweet coltsfoot. Other varieties of P. japonicus include giant Japanese butterbur and variegated Japanese butterbur. Common names for other species in the family include sweet butterbur, white butterbur, common butterbur or bog rhubarb, winter heliotrope, arrow-leaved coltsfoot, and western coltsfoot. The genus name derives from a Greek word for felt hats worn by shepherds, and the common name "butterbur" supposedly stems from a former practice of wrapping butter with the plant's leaves.
Petasites hybridus — the common butterbur or bog rhubarb — is sometimes used to treat migraines. Studies have found that extract from the common butterbur plant reduces migraine occurrence by 48 percent. Butterbur extract also did not have severe side effects. The root of common butterbur has been used as a homeopathic heart stimulant and remedy for fevers and colds.
Most species of Petasites can reach between 18 and 36 inches (about 45 and 90 centimeters), depending on the variety, but the giant Japanese butterbur can range from 4 to 6 feet (about 1.2 to 1.8 meters) tall. The plants bloom in late winter or early spring, before leaves appear. Flowers grow in clusters on thick stalks and have colors ranging from white to light pink to magenta, depending on the species. The blooms attract butterflies, birds, and bees. Large, heart-shaped leaves appear when the blooms begin to die off — the leaves can reach up to 3 feet (about 0.91 meters) in diameter.
Members of the Petasites family like to grow in soil that is always moist or even wet; when grown in gardens, they should be watered frequently. The plants can grow in soil that ranges from mildly acidic to alkaline and in partial shade to full sun. Butterbur varieties are hardy down to a temperature of -20°F (-28.8°C).
Butterbur spreads aggressively, and thus should be planted 3 to 4 feet (about 0.91 to 1.2 meters) apart. It is often considered a nuisance weed or invasive plant where it is not wanted because of the spreading. The spreading can be controlled in a garden by planting the plants in a sunken metal or plastic tub.