National Collection of Hardy Dwarf Gunnera
The family Gunneraceae contains just one genus, Gunnera, comprising 63 species. They are mostly found in wet or high rainfall habitats in the Southern Hemisphere: in Tasmania, New Zealand, New Guinea, the islands of SE Asia, Hawaii, Africa and Madagascar, with around two-thirds of the total in Latin America.
The best-known Gunnera in cultivation are the two largest species, G. tinctoria and G. × cryptica, sometimes known as ‘Giant Rhubarb’; fine examples of G. × cryptica line the driveway leading to Natural Surroundings. Their leaves can be more than 3m across and when they emerge in the spring the giant leaves and huge flower spikes seem almost prehistoric – a scene from Jurassic Park. Many Gunnera are rather smaller, however, and only a few are hardy, and our collection focuses on these.
Gunnera cordifolia - native to the island of Tasmania in Australia
Gunnera Facts
* The genus is named after Johan Ernst Gunnerus (1718–1773), a Norwegian bishop and botanist.
* All Gunnera are herbaceous, non-woody perennials: despite their size, even the giant Gunnera die right down in winter.
* The flowers are wind-pollinated and neither large nor colourful. In some species they are clustered together into conspicuous spikes.
* In many Gunnera male and female flowers are found on separate plants.
* The fruit is a berry, with a fleshy outer layer surrounding an inner stone containing the seed.
An Ancient Lineage
Amongst living plants the family Gunneraceae is one of the more ancient – fossilised pollen suggests an origin in South America at least 95 million years ago, and Gunnera have survived more or less unchanged ever since. For context, the first flowering plants appeared 150–250 million years ago.
A Remarkable Spread
Within 10 million years of their first appearance in South America, Gunnera had spread widely, with fossil pollen discovered in areas where they are not found today, such as western North America, mainland Australia, and Antarctica. Until recently it was thought that Gunnera had spread from South America all across the ancient super-continent of Gondwanaland and that their modern scattered distribution is a ‘relic’ following the break-up of the Gondwanaland to form the modern southern continents. Genetic reconstruction of the Gunnera family tree indicates, however, that the timings don’t match.
It is now thought that the majority of Gunnera species, even those found on entirely different continents, diverged from each other relatively recently, well after the break-up of Gondwanaland. For at least some the modern distribution is the result of long-distance dispersal from South America across the oceans. How this happened is a mystery.
A Special Relationship
The majority of plants form intimate relationships with soil fungi. Fungi pass nutrients to the plant and receive carbohydrates, the product of photosynthesis, in return. A few groups, notably the pea family, form a relationship with bacteria, which provide the plant with nitrogen. The Gunnera are one of only two families of flowering plant to form a relationship with cyanobacteria. Like plants, cyanobacteria – popularly known as ‘blue-green algae’ – can produce energy via photosynthesis, and some can also fix atmospheric nitrogen, making it available for growth.
In its relationship with Gunnera, the cyanobacteria provides the plant with fixed nitrogen. In return, the Gunnera provides a protective environment and stable source of nutrients. The relationship is very close – the Gunnera is dependant on the cyanobacteria for nitrates, which are essential for growth. Only one other flowering plant has a similar relationship (Oryza – in the grass family); all the other plants associated with cyanobacteria belong to even more ancient lineages, including mosses and liverworts, aquatic ferns and cycads.
Giant Gunnera
Two species of giant Gunnera were introduced to Britain and Europe in the 19th century, both originating from South America: G. tinctoria from the wetter parts of Chile and SW Argentina and Gunnera manicata from the Atlantic rainforest zone of southern Brazil. These large, striking plants were a favourite in gardens with plenty of space and widely planted. Both have, however, ‘escaped’ and now grow in the wild, in damp, often shady places, including sheltered sea cliffs and along streams by the sea. Both are long-lived and develop massive rhizomes, and both produce large spikes of small, wind-pollinated flowers.
Fairly quickly it became obvious that the two species of giant Gunnera behaved differently. Gunnera tinctoria was the more prolific, reproducing via seed and spreading easily, especially in wetter regions: it is now seriously invasive in coastal regions of W Ireland, Cornwall (as in the photo) and the Outer Hebrides. Due to its invasive nature tinctoria was outlawed in 2017 and it is now illegal to sell it, or to plant or otherwise cause the species to grow in the wild. Gunnera manicata, on the other hand, was much more demure: reproduction by seed has not been reported in Britain and vegetative increase is slow. In fact, most ‘wild’ populations of manicata actually originate from planted specimens.
Distinguishing the two ‘giant rhubarbs’ has long been regarded as challenging and their identification has been carefully studied over the years. The native ranges of the two species of giant Gunnera do not overlap and they cannot hybridise in nature, but when grown together in Europe this became possible and hybrids appeared in cultivation from the late 1870s onwards, making identification even more complicated. Then, in 2022 a study based the appearance of the plants as well as their history in Europe shed light on why things were so difficult. It concluded that genuine Gunnera tinctoria were growing in Britain and Ireland, but G. manicata was no longer present, having been replaced by he hybrid between G. manicata and G. tinctoria. The hybrid was given the name Gunnera × cryptica and the spectacular plants growing along the drive at Bayfield are this hybrid – they never seem to set seed have been propagated over the years by dividing the rootstock.
Genetic studies published in 2023 confirmed that all the sampled ‘manicata’ from Britain and Ireland were indeed the hybrid and pointed out that when they were thought to be G. manicata it was perfectly legal to grow and sell the plants, but now that they have been identified as the hybrid G. x cryptica, they are covered by the same laws as the G. tinctoria parent, making it illegal to sell them or even cultivate them!
The irony is that the plants now known as G. x cryptica are largely infertile ‘there have been no reports of it becoming problematic in the wild'. Happily, existing plants do not need to be destroyed, although Gunnera × cryptica must not be newly planted or cultivated, so the plants along the drive can continue to inspire and impress for the foreseeable future.