Giant rhubarb (Gunnera tinctoria) identification
What is Gunnera? Read through our Gunnera identification guide below. If you are still unsure, email us your photos and we will confirm whether it is Giant rhubarb for FREE
With leaves that grow to 2 metres in diameter, the Gunnera plant or Giant rhubarb is increasingly becoming a nuisance in the UK, especially in the southwest of England. It thrives in damp habitats and can quickly overwhelm other plants causing damage to local ecosystems
What is Gunnera?
Gunnera is a group of herbaceous flowering plants, which means they don’t have woody stems above ground. It appears like the leaves are simply bursting from the soil. There are about 64 different plants in the genus and Gunnera tinctoria is the most problematic in the UK. Native to regions like South America and the Asian Pacific, the stalks of the Gunnera plant are edible as the more common name giant rhubarb might suggest, although they are in completely different families.
Gunnera is an old plant in evolutionary terms and fossils exist from as far back as the Cretaceous period, which may point to its hardiness. Gunnera manicata, which often goes by the nickname dinosaur food, was first introduced to the UK in 1867.
Gunnera tinctoria mostly hails from the south of Chile and Argentina where it is commonly used as a source of food. The stalks are used in salads, for marinades and even for making beer.
In the UK, it is not widely known for its culinary uses. Outside of a garden setting, where it is prized for its bold architectural form, it is mostly found in the wild, in places like coastal cliffs, riverbanks and roadsides. Although more common further south, there are now problems with Gunnera tinctoria as far north as Scotland, where it was first introduced to gardens in the Hebrides in the 1980s. Since then, it has spread widely and threatens agricultural land and native habitats.
Like Japanese knotweed, Gunnera spreads through rhizomes in (the root system underground). Digging up the plant can help control it but if even a small part of a rhizome survives in the soil, it is likely to grow again.
The plant is also dispersed locally through seeds carried on the wind and when plants are thrown away in the wild by less conscientious gardeners. A single Gunnera plant can produce as many as 250,000 seeds.
The other big problem with a plant like Chilean rhubarb is that it grows very quickly. On roadsides and riverbanks, rhizomes can spread into drains and ditches causing damage. As winter comes, the Gunnera plants die back, leaving large patches of bare soil that can then be susceptible to erosion in natural habitats.
Gunnera tinctoria is now listed in Schedule 9 of the Wildlife and Countryside Act which means it cannot be sold by garden centres and gardeners need to control the plant if they have it and ensure it does not spread outside their boundaries.
What does Gunnera tinctoria look like?
Gunnera tinctoria or Giant Rhubarb
Also called Chilean rhubarb, the plant is prevalent in areas like South America but has found its way around the world, including here in the UK. The large leaves have jagged or irregular margins and are a little darker than other varieties such as Gunnera manicata. Plants reach around 2m in height when fully grown
The stalks on mature plants are reddish or purple and have green bristles. When the flower spike grows, it is a deep crimson colour and there can be up to about 4 of these, more than a metre long, on each plant.
The plant produces red panicles, or cones of small flowers – once these become pollinated, they produce small reddish berries which finally turn into black seeds. The flower spikes start to form around May, and can be a metre in length. The berries and seeds start to form as we head into the Autumn.
The plant has upright, prickly stems that can be quite painful if you pick them up by hand. On young plants these tend to be greenish but as they matures the stems turn a red or purple colour.
Gunnera has large, umbrella-like leaves that can be up to m wide on mature plants. If you turn over the leaves, tinctoria has trichomes (hairs) on the main leaf nerves and the veins at the base of the leaf are purple.
Use our extensive guide how to remove gunnera
How to remove Gunnera?
Why is Gunnera a problematic invasive species?
There are two ways that Gunnera tends to spread:
- Locally, the rhizomes or root system below the ground grows rapidly. While with Japanese knotweed this is a major issue because it can grow next to important infrastructure, it’s not such a problem with Gunnera as it needs damp, almost boggy conditions to thrive. If these rhizomes do get near buildings and walls, however, they can cause substantial damage. The Gunnera rhizome network can also grow down to a depth of up to a metre which can make them difficult to excavate.
- Giant rhubarb produces metre-long panicles of flowers that turn into berries and then small black seeds. There can be thousands and thousands of these, every autumn. These seeds get carried by birds, blown on the wind, and distributed in many ways.
If seeds land in the right place, they can fundamentally alter the ecosystem of that location because of the rhizome system and the overwhelming size of the plant above ground. A dense colony can develop over a few seasons and once established is difficult to eradicate. The problem with plants that have an expanding system of rhizomes beneath the soil is that you must get rid of all traces to prevent them from growing back.
The major problem is not with individual gardens but where the plant is likely to spread to and the damage to local ecosystems that can be caused. While it’s not an offence to grow the Gunnera in your garden under Schedule 9 of the Wildlife and Countryside Act in England and Wales, it is against the law to allow it to expand beyond your boundaries.
There are around 63 distinct types of Gunnera around the world, mostly in more southern regions, though this is changing.Gunnera tinctoria, for example, has been found much further north in the last 50 to 60 years, likely a result of climate change. Some species are hardier than others, but they require a lot of water which is why you find them near ponds, rivers and bogland.
You cannot miss most species of Gunnera as they are quite large and imposing. They have leaves that can be as much as 2 metres wide and the whole plant looks like a more gigantic version of our traditional rhubarb.
The Gunnera manicata is still a popular choice in larger gardens where there is a pond or stream nearby, but they are not often found in smaller gardens, unless by accident. People who do have the plant on their property, however, need to make sure that they collect the seeds and don’t allow them to spread.
There are some variations between types of giant rhubarb, notably their size – but the unmistakable jagged-edged leaves, with deep veins sitting on upright, prickly stems are shared by all plants in the family – making them easy to identify.
Gunnera manicata or Brazilian Giant Rhubarb
Again, prevalent in South America, the leaves of the Gunnera manicata look similar but are less ragged and slightly narrower than the Gunnera tinctoria. The stalk is pale green, and the spikes are a reddish hue. The flowering spike is a little more sprawling than its close relative and is wider than it is longer, growing near the ground. The flowers are greenish yellow rather than red or crimson.
Gunnera Megellanica or the Devil’s Strawberry
Not all Gunnera are prehistorically huge and impressive. The Gunnera megallanica can be considered the dwarf version as it only grows a few centimetres tall.
It has kidney-shaped dark green leaves with fine hairs and produces clusters of small red berries that give the plant its more common name, the devil’s strawberry. While not on any lists, Gunnera megellanica can become invasive if not tended to properly.
Plants that look like Gunnera
While Gunnera or giant rhubarb is fairly distinctive, there are a few plants that resemble it, and which are largely not considered invasive. These include:
- Burdock or Arctium Asteraceae
Burdock is often mistaken for giant rhubarb (it’s called wild rhubarb in some places) as it can grow up to about a couple of 2 metres in height. It has less ragged leaves and it does not produce flowers but prickly burrs or thistles.
- Swiss Chard or Beta Vulgaris
With its bright purple stalks, if you’re not concentrating Swiss chard can look like a new growth of Gunnera but it’s quite different once you get up close. The leaves have a much less ragged at the edge and the plant only grows to a few feet in height. It’s also a reliable source of potassium and can be used in cooking.
- American Skunk Cabbage or Lysichiton Americanus
This is a colourful plant and can be mistaken for Gunnera primarily because it grows around waterways and is also classed as an invasive species by the Government. There are big differences in how they look, however, and the stems are generally green, the leaves a lot narrower and thicker and it produces bright yellow flowers.
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