About Gunnera manicata Linden
Gunnera manicata Linden, commonly called giant rhubarb, is a large, clump-forming herbaceous perennial that reaches 2.5 meters (8 feet) tall and spreads 4 meters (13 feet) or more wide. This species produces impressively large leaves: leaves with diameters well over 1.2 meters (3 feet 11 inches) are common, and a mature plant can have an overall leaf spread of 3 by 3 meters (10 feet by 10 feet). The largest recorded leaf of this species reached up to 3.4 meters (11 feet) in width. It is the largest Gunnera species by size, though it is not the tallest, a distinction that belongs to Gunnera masafuerae. Small spikes cover the underside of its leaves and its entire stalk. In early summer, it produces tiny red-green dimerous flowers arranged in conical branched panicles, which are followed by small, spherical fruit. Like most gunneras, G. manicata forms a symbiotic relationship with certain blue-green algae that fix nitrogen to provide for the plant. Despite its common name giant rhubarb, it is not closely related to true rhubarb. The genus is named after Johan Ernst Gunnerus, a Norwegian bishop and naturalist who also named and formally described the basking shark. G. manicata is native to the Serra do Mar mountains of coastal Santa Catarina and Rio Grande do Sul states, Brazil, where local communities use it in traditional medicine to treat sexually transmitted diseases. Most cultivated and feral plants growing in Western Europe that were previously identified as G. manicata have actually been replaced, fully or largely, by the hybrid Gunnera × cryptica. Giant rhubarb became widely cultivated as an ornamental garden plant in the United Kingdom and Ireland, grown primarily to showcase its massive leaves. It grows best in damp conditions, such as near garden ponds, and it is intolerant of cold, wet winter conditions. In 2022, the Royal Horticultural Society confirmed that most plants cultivated as G. manicata in the region were actually Gunnera × cryptica, a hybrid of G. manicata and the highly invasive Gunnera tinctoria. In December 2023, the UK Department for Environment, Food and Rural Affairs banned Gunnera × cryptica: it may no longer be sold or cultivated in the UK, and gardeners who already have the plant must prevent it from spreading.
