Gunnera and Skunk Cabbage

Two more noxious plants in the parish.

(See also information on other noxious plants of the parish website)

There are 36 plants that are deemed to be Invasive Non-native Plants in the UK as they spread rapidly and threaten ecosystems, habitats or native species. They include Japanese Knotweed, Himalayan balsam, water hyacinth and giant hogweed.

Last December giant rhubarb Gunnera was added to the list.

It is now an offence to sell, import or plant giant rhubarbs Gunnera tinctoria and Gunnera × cryptica or cause them to grow in the wild. Gunneras are much loved for their huge, exotic-looking leaves that can measure up to 4m in height in summer. Introduced by the Victorians, these moisture-loving bog plants are a familiar sight in many historic gardens, parks and botanical collections, and are often found growing alongside lakes, ponds and streams. New advice from the Department for Environment Food and Rural Affairs (Defra) has said they should be treated as banned species. Thus Defra’s public guidance states that no offence is committed if a listed plant is growing in your garden or on your land. However, you cannot intentionally plant listed species on your land or intentionally cause existing listed plants to spread, or sell, use or exchange any listed species. Therefore the Royal Horticultural Society is changing its advice as follows. If gardeners do want to remove it, it can be cut back and treated with herbicide or dug out completely. Alternatively, an easy way to stop it from spreading is to cut flower heads each summer before they set seed, then compost with care. In drier areas, the moisture-loving plants need a lot of watering, and this may fall under the definition of cultivating, so many of the plants across the country will have to be allowed to die out.

Another invasive alien found in the parish is the American Skunk Cabbage Lysichiton americanus.
American skunk cabbage was first mentioned as present in the UK in 1901. It is not particularly abundant being rather a specialist, requiring wet ground to thrive such as the banks of shallow streams and brooks. Characterised by enormous leaves and a stout flower spike enveloped in a bright yellow shroud, it announces its presence by exuding a distinctive aroma.

The implications of this are the same as for Gunnera species in that in the UK, selling or planting, or even keeping American Skunk Cabbage in a garden is banned. If the plant is present on your land, you have a responsibility to take concerted action to contain it and prevent its spread. Its ability to seed after five years and establish deep rhizomes has elevated the questions of how to control and get rid of it. On waterways it can become dominant and the ecology of these locations is forced to change. The whole food chain can be impacted there. As the leaves contain oxalic acid like rhubarb, not many animals will eat it except a few slugs! Control measures would be similar to those for Gunnera.