The giant rhubarb has been a beloved garden plant for many centuries, admired for its striking leaves and expansive form. It is often found in the gardens of grand homes and various National Trust properties.

The UK government has decided to implement a prohibition on the well-liked plant, also referred to as Gunnera. This means that it cannot be bought or grown, and individuals who possess it in their gardens must take measures to prevent its spread. The plant will be subject to a similar restriction as Japanese knotweed.

For a long time, it was thought that the large Gunnera plants found in Britain were either Gunnera manicata or Gunnera tinctoria. The former is a harmless and attractive plant that comes from Brazil and Chile, while the latter is a very invasive species that quickly takes over and harms native plants. Since 2010, it has been illegal to sell or grow G tinctoria, but G manicata (or plants that are believed to be G manicata) have been popular and praised for their unique appearance.

A recent research conducted by the Royal Horticultural Society used molecular and morphological analyses, along with a historical investigation, to uncover that G manicata was likely no longer being cultivated shortly after its introduction. Instead, the researchers discovered a hybrid of G manicata and G tinctoria, which has been given the name Gunnera × cryptica.

This particular species is considered to have a similar level of invasiveness as G tinctoria and will consequently be prohibited. There are concerns that the widespread distribution of this plant may lead to issues, similar to those caused by G tinctoria in wetter regions like the west coast of Ireland and Scotland. It has been classified as a “species of union concern” according to an EU regulation, and is currently designated as a matter of “special concern” in the UK.

Currently, there are various groups of Gunnera plants throughout the United Kingdom and it is commonly used in gardens. Due to this, the RHS predicts that there will be significant consequences for the horticultural industry and collections in the UK.

The Department for Environment Food and Rural Affairs (Defra) has released new guidance stating that the hybrid plant should be considered a prohibited species. As a result, the RHS is revising their instructions to gardeners regarding G manicata plants, which are highly likely to be the invasive hybrid. This includes removing them from stores and identifying any of the hybrid plants in their gardens.

If any plants are kept in RHS gardens, there will be noticeable signs with relevant details about their status, and gardeners will be advised not to plant them in their own gardens. According to Defra, current plants may remain, but Gunnera × cryptica should not be newly planted or grown in gardens.

In arid regions, the plant that thrives in moist conditions will require frequent watering, which falls under the category of cultivation. Consequently, numerous plants throughout the nation will have to be left to perish.

John David, the leader of horticultural taxonomy at the RHS, stated that during their study, they initially utilized Gunnera to examine the challenges in distinguishing between invasive species and their non-invasive counterparts. However, it was unexpected when they discovered that a plant commonly enjoyed in gardens for its large size and unique appearance was actually a previously unrecognized hybrid.

Without the assistance of botanists from Brazil and Chile, who provided essential materials, we would not have been able to demonstrate the extinction of one species and the identification of a new hybrid.

The findings were featured in the publication Sibbaldia.

Source: theguardian.com