Scientists Find Rare Japanese Knotweed Species in South Wales



October 16, 2019

Conolly's Knotweed Seedling

Japanese Knotweed Hybrid

During a recent study of a large field test site near Cardiff, South Wales, a team of scientists from Swansea University, led by PhD Student Sophie Hocking, discovered a rare species of Japanese Knotweed (Reynoutria japonica), known as ‘Conolly’s Knotweed’ (X Reyllopa conollyana), a hybrid of Japanese knotweed and Russian vine.

The research team from the Department of Biosciences planned to study:

  • the long term environmental impact of effective R. japonica control;
  • secondary invasion processes by less invasive species, such as 'Indian balsam';
  • habitat restoration tactics for areas previously degraded by invasive species, specifically in Europe.

Conolly's Knotweed Hybrid

Since Japanese knotweed plants in the UK derive from a single female clone, it was thought that they could not be effectively fertilised without a male plant, and the spread of this invasive species is via the fast-growing rhizome which may lie dormant underground for up to 3 years.  However, the very fact that Conolly’s Knotweed was been discovered in a seedbed at the test site means that hybridisation has taken place (fertilisation by another knotweed species).

Surprise Discovery

Sophie Hocking and the Swansea University team said they were surprised by the discovery of this rare species of Japanese Knotweed since, ‘’we actually didn’t expect to find any type of viable invasive knotweed seed, because it’s extremely unlikely for any to survive wet UK winters”.

Other Hybrid Knotweed Encounters

This is not the first time Conolly’s knotweed has been discovered in the UK. In 1983 it was found in Middlesex and another location in Wales. This obviously means there is a concern that hybridisation could occur on a greater scale throughout the UK and cause further problems with regard to the spread of Japanese Knotweed.

Ongoing Research Studies

With growing concern from homeowners, commercial landowners and developers alike, ongoing research studies such as the one being performed by the university are vital to helping us better understand how to manage, control and eradicate Japanese knotweed in the UK.

And thus the saga continues!