Sales of leafy giants are outlawed as new study unmasks hybrid imposter, reports Ian Hodgson
Sales of giant Chilean rhubarb are now banned in England and Wales after an RHS study revealed an unrecognised and invasive hybrid.
RHS scientists had been investigating the two largest and most widely planted species, Gunnera tinctoria and G. manicata – both popular pondside plants due to their 2m wide leaves.
G. tinctoria was introduced in 1839 from South America. It was identified as invasive and blacklisted in 2017 after colonising areas such as the west coast of Ireland and Scotland, spreading from copious seed shed.
G. manicata was considered benign, but the RHS research, which involved DNA study, found the species was lost from cultivation shortly after its introduction in 1867. In its place, researchers identified an unrecognised hybrid between G. manicata and G. tinctoria, now named as Gunnera x cryptica.
Hardier than G. manicata, it has been unwittingly selected and sold in the trade as that type, but is considered by the RHS to be as invasive as G. tinctoria.
John David, RHS head of horticultural taxonomy said: “When we began our research, we were using gunnera to look at the difficulties in differentiating between an invasive species and non-invasive close relatives. It was a surprise to find a plant that has been a firm favourite in gardens for its impressive size and exotic appearance turned out to be an undetected hybrid.”
The RHS warns that plants previously labelled as G. manicata are likely to be Gunnera x cryptica. It has identified such plants in its gardens and removed them from sale.
The Department for Environment, Food and Rural Affairs (DEFRA) advises gardeners to
