Family: Gunneraceae
Common name: Giant rhubarb, Brazilian giant-rhubarb
Giant rhubarb is one of the largest herbaceous plants very commonly seen in Europe and UK, near ponds, streams and water bodies. They are native to Brazil and was introduced to many other countries, but are now considered invasive plants that are banned in few places.
Plant Characteristics
These plants are huge, growing to a height of 2.5 meters with a spread of 3-4 meters. They are capable of forming towering clumps with new plants growing from the rhizomatous stems, allowing the plant to fill large areas.
The leaves are large, puckered, hairy, with deep lobed margins. They can grow to a diameter of 3 meters spreading like a huge umbrella. The stalks of Giant rhubarb leaves are thick and covered with spines, which are also seen on the lower surface of the leaves.
During summer, the Giant rhubarb plants produce numerous small reddish-brown flowers that later turn into small berry-like fruits. These fruits are initially green, turning deep red as they ripen. Each fruit contains numerous tiny seeds that help in propagation.
Gardening Tips
Giant rhubarb plants prefer moist or wet soil which is rich in humus, and hence they are commonly seen near ponds, water bodies, or bogs where the soil does not dry out.
They can grow well in full sun or partial shade. Once established in the soil, Giant rhubarbs need zero maintenance provided they have a steady supply of water.
These plants form large, dinosaur-era-like clumps that gradually spread encroaching into nearby spaces and choking other vegetation.
For this reason, these plants are now banned in the UK, where gardeners are not allowed to sell or cultivate Gunnera manicata or Giant rhubarb. The main reason is that the current species that seems to be grown in gardens is a hybrid between Gunnera manicata and Gunnera tinctoria, the latter one being very invasive.
The stalks of Giant rhubarb were eaten as famine food, and the plants were used in the treatment of sexually transmitted diseases. However, there is no scientific evidence to the effectiveness or the method of this treatment.
In current times, they are primarily grown as ornamental plants, loved for their gigantic leaves and fast growing habit.
Interestingly, the Giant rhubarb plants exhibit nitrogen-fixing capabilities of the Fabaceae or pea family, the roots containing nitrogen-fixing bacteria that convert atmospheric nitrogen into nitrates and nitrites that can be absorbed by plants.
Propagation
Propagation is by seeds or root division. Left alone, the Giant rhubarb plants will produce small plants from their spreading roots, which can be gently removed from the soil without breaking the roots, and replanted.
Photographed at: KEW Botanical Garden, London
