Invasive banned species confirmed to be present in Winchester

The plant, a Gunnera or giant rhubarb, is growing in The Weirs, near Wharf Mill. It has grown to around ten feet tall with leaves around three feet wide.

It was added to the UK Government’s invasive species list in late 2023, meaning that it cannot be sold or cultivated, and where it is already planted care must be taken to ensure it does not spread.

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The Gunnera in the Weirs (Image: Chris Atkinson)

A city council spokesperson said that the Gunnera is yet to show any issues, saying: “The Gunnera in question has been in place for several decades and has not, to our knowledge, presented any issues to date.

“We are aware that the Gunnera was added to the invasive species list in December 2023, and are following the Defra advice in the management of the plant.”

A spokesperson for Defra, the Department for Environment, Food and Rural Affairs, told the Chronicle that Gunnera is listed as a “species of special concern”.

These species cannot be kept, permitted to breed or reproduce, transported, sold, or released into the environment. It is also an offence to plant or otherwise cause listed species to grow in the wild.

The Defra spokesperson continued: “Pure Gunnera manicata are not banned and where this species can reliably be sourced then sellers can freely use this species, however, the findings of the Royal Horticultural Society (RHS) indicate that current stocks are actually either banned species or hybrids of banned species and therefore should not have been and cannot continue to be traded.”

Fran Clifton, head gardener of Sir Harold Hillier Garden, near Romsey, said it is unlikely for the Gunnera on The Weirs to spread if it is properly maintained.

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She said: “Seeding could potentially be a problem, but it’s not at the moment – it’s not like other weeds such as Himalayan Balsam which spreads like wildfire. It’s about people who have them by their garden pond being responsible.

“For instance, here at the gardens – because we’ve got it too – when it flowers and when it has finished flowering and the seeds start setting we remove the seed cones. This is because our pond is linked to a watercourse, and we don’t want those seeds going into the watercourse.

“The seeds could drop into the river (Itchen), but the people who look after the Gunnera should be removing those seed cones. It’s not necessarily a huge alarm or required that they remove the plant, there’s no need for that. As long as they are responsible with it.”

Gunnera manicata, known as Brazilian giant-rhubarb or giant rhubarb, originated in the coastal mountains of Santa Catarina, Parana and Rio Grande do Sul States in Brazil.