EPPO Global Database

EPPO Reporting Service no. 10 - 2019 Num. article: 2019/218

The rare hybrid x Reyllopia conollyana is identified in a seed bank study in Wales (GB)

x Reyllopia conollyana is a hybrid between Fallopia japonica and F. baldschuanica (Polygonaceae – both EPPO List of Invasive Alien Plants).  The hybrid has been recorded in a few locations in Germany, England (GB), Hungary and Norway (EPPO RS 2019/151). In 2018, in Taff’s Well near Cardiff (South Wales), as part of a large field experiment assessing integrated pest management techniques for the control of F. japonica, soil samples were collected from beneath invaded sites and placed in controlled conditions to evaluate the regeneration of the native seed bank. Interestingly, an unidentified knotweed species emerged from the soil with no visible rhizome material attached.  The seedling was subsequently identified as x Reyllopia conollyana. The low number of records of the hybrid in the natural environment may be a result of mild winters and an underdeveloped endosperm that can make the seed susceptible to attack from soil mycobiota.  Potentially, with climate change, the occurrence of x Reyllopia conollyana may become more frequent in the future. 


Hocking S, Jones D, Eastwood D (2019) Out of sight, out of mind? Ex-situ germination of x Reyllopia conollyana (Conolly’s knotweed) in a South Wales invaded seed bank. Botanical Society of Britain and Ireland 142, 52-55.