Gunnera tinctoria – January 19th 2026 – Giant Rhubarb

The Giant Rhubarb is a spectacular plant introduced to British gardens in 1849 from the west coast of South America and first recorded in the wild in 1886. An alternative name is Chilean Rhubarb. Although not related to rhubarb, it continues to be used in Chile in the same way that we use rhubarb, although the stalks need to be peeled to remove the spines. After peeling, the stalks are eaten fresh or cooked to produce jam or cordial. I’ve never tried doing this, but I might gather some stalks in the summer, make a little jam and try it out on gastronomic friends and relatives.

Illustration to show the size of the fully-developed leaves. The human subjects are 1.6 metres tall, roughly equal to the diameter of the leaves.

It reproduces both by seed and by rhizomes, and it has colonised many sites on the west coast of Scotland and Ireland.  Just how big does it get? It can be 2 metres tall and the leaves may expand up to 2 metres across. It commonly forms dense thickets that shade out all other plants. It has a reputation of being invasive in UK and Ireland, Europe, south Australia including Tasmania, New Zealand and parts of the USA. It is banned from sale in Britain and Europe. In UK it is listed in Schedule 9 of the Wildlife and Countryside Act 1981 as an invasive species.

An early stage of canopy development. Flowers develop early on and arise directly from the rhizomes (as the leaves do as well). Note the soil is covered with a thick layer of dead and rotting leaf stalks from the previous year. From the Lost Gardens of Heligan, Cornwall. Image: Chris Jeffree.

It is both a thirsty and hungry species, requiring generally wet conditions, hence it grows well on our west coast, especially in the milder areas including Cornwall and Devon and the west coast of Ireland. In Botanical Gardens and on large estates it is generally planted next to a lake or where the ground is soggy. In the wild it colonises riverbanks, woodlands, coastal cliffs, roadsides, quarries and ditches. It can grow close to the sea and must have a fair degree of salt tolerance. Atmospheric humidity may be important too – in Chile the area it occupies is often misty.

A view under the canopy. The dense shade prevents other species from growing and contributes to the invasive nature of the plant. Image: Chris Jeffree.

In Britain and Ireland, it is naturalized where annual rainfall exceeds 1100 mm, with average winter temperatures ranging from 3 to 6 °C, and average summer temperatures between 12 and 15 °C. (Osborne et al. 1991). In Chile, the average conditions are slightly cooler (11 °C) and the mean annual precipitation is 1335 mm (calculated from data in Osborn’s article). Soil pH is somewhat acid, between 4.6 and 5.9.

Developing inflorescence. The compact form and red colour indicate G. tinctoria but the spines on the underside of the leaf suggest G. manicata. Image: Chris Jeffree.

A remarkable feature of Gunnera is that its tissues contain Nostoc, the filamentous nitrogen-fixing bacterium. Gunnera is the only know angiosperm genus forming a symbiotic relationship with Nostoc. It is likely that the plant gets most of its nitrogen from Nostoc. An excellent and highly readable account, readily downloadable, is by Osborne et al. (1991).

Frosted leaves, Threave, Dumfries & Galloway. The plant dies down in winter and resprouts in the Spring. Image: Chris Jeffree.

There is a very similar Gunnera which does not form viable seeds in British conditions and has a slower rate of vegetative spread – Gunnera manicata, known as Brazilian Rhubarb and native to southern Brazil. In UK it is thought to be rare in the wild and its leaves are even bigger than those of its Chilean relative – more than 2 metres across and more deeply divided. Telling the difference between the two has been challenging for BSBI’s Recorders, and this remains so for most of us. The challenge is accentuated as the colour, size and form may depend on the stage of growth and the availability of water and nutrients. The Floras of Stace (2019) and Clapham et al. (1989) are helpful, but the most accessible explanations of the differences are from authors who show photographs or artwork. The renowned botanical illustrator Lizzie Harper has made illustrations for the Field Studies Council – they nicely emphasise the difference. Alternative sources include the 11-minute You Tube movie from a garden expert in Yorkshire, and the website of a German group here. But unless you find the two species growing side-by-side it will often be a challenge to tell the difference. In the table at the end of this article I’ve listed the differences mentioned in various sources.

Gunnera tinctoria in Britain and Ireland. Note the predominantly western pattern. From BSBI/Maps.

I confess that we have found it difficult to distinguish the two species from the many photographs we have taken in botanic gardens over several years. Herbarium specimens are rare because the plants are huge. I was both shocked and relieved to discover a recent research article based on analysis of chloroplast DNA which states “G. manicata appears no longer to be present in Britain and Ireland. Instead, the plant under this name is G. × cryptica, a hybrid between G. manicata and G. tinctoria”. This may explain all difficulties of field-based identification – we have often been dealing with hybrids.

References consulted

Clapham et al. (1989) Flora of the British Isles. Cambridge.

Edwards D et al. (2022) An investigation of large-leaved Gunnera L. (Gunneraceae) grown outside in Britain and Ireland. Sibbaldia: the International Journal of Botanic Garden Horticulture 22, 1-22.

Gioria M and Osborne BA (2013).  Biological Flora of the British Isles: Gunnera tinctoria. Journal of Ecology. 101, 243–264.

Osborne, Bruce, et al. (1991) Gunnera tinctoria: an unusual nitrogen-fixing invader. BioScience 41.4, 224-234.

Rai AN et al. (2000). Tansley review no. 116 cyanobacterium–plant symbioses. The New Phytologist, 147(3), 449-481.

Stace CA (2019) New Flora of the British Isles. C&M Floristics. 

Silvester, W.B. & Smith, D.R. (1969) Nitrogen fixation by Gunnera-Nostoc symbiosis. Nature, 224, 1231

Sykes WR (1969) Gunnera tinctoria and Gunnera manicata. J Royal New Zealand Inst Horticulture, 1, 56-59.

©John Grace