Gunnera is a family of about 50 herbaceous plants, many of which have extremely large leaves that can be as much as 4 feet (1.2 m) or more in diameter. The flowers are tiny and insignificant and appear in late spring and summer. These plants are native to mountainous areas of Africa, Central America, and South America and are tender perennials that cannot tolerate cold weather. Giant rhubarb is the most commonly known member of the Gunnera family. Most of these types of plants prefer to grow in shady areas that are near water.
These tender perennials should be dug up and moved indoors in winter if possible. It is not easy to move these large plants, however, so the bare roots may be kept dormant in a dark place until they can be replanted outdoors in spring. Plants can be put into pots in a cold frame for the winter because they provide protection from the cold wind that can damage or kill Gunnera plants. The plants can also be cut back to ground level and covered with a thick layer of mulch for protection from the cold.
Most varieties of Gunnera can be grown from seed, although they may not germinate for several weeks. New plants may also be started by removing small offshoots that appear on the sides of the plant stalks, and planting them. They should be planted at least 6 feet (1.8 m) apart to allow for growth. These plants require a humus rich, very moist soil and are good choices for larger water gardens or boggy areas. Gunnera plants have spiny leaves and stems that can cause skin irritation, and gloves should be worn when handling any part of this plant.
Some species are highly invasive and can be all but impossible to eliminate once they have begun to spread. This is usually not a problem in colder climates as the plants will not survive when left outdoors for the winter. Care should be taken, however, when they are planted in areas where they are left in the ground year round.
Several members of the Gunnera family are grown as medicinal plants. Gunnera perpensa is often used as a homeopathic gynecological treatment in southern Africa. It is said to induce labor and help to expel the placenta after childbirth. Gunnera tinctoria has astringent properties and is used in South American countries to treat psoriasis and other skin conditions.