Invasive species are widely recognized as one of the primary direct contributors to biodiversity loss worldwide. Consequently, it is of global importance to understand the mechanisms underlying their invasion success.

Reynoutria japonica, also known as Japanese knotweed, is native to Eastern Asia and is a highly invasive plant species in Europe and North America. The invasion of the species brings substantial damages to infrastructure and ecosystems, however, the mechanisms for its high invasiveness are still not fully understood.

In a study published in New Phytologist, an international team includes researchers from where Japanese knotweed is native (China and Japan) and introduced (Germany and USA), investigated plants from a large number of populations of this global plant invader, to elucidate the reasons behind its invasion success.

The growth and clonal reproduction of 128 R. japonica populations (55 from native range China and Japan, and 73 from introduced North America and Europe) were compared in two common gardens, one located at Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences (CAS) and the other at Fudan University, both in China.

The researchers found that the R. japonica plants from the introduced ranges did not exhibit larger sizes compared to their counterparts. Plants from all four ranges demonstrated almost equivalent aboveground biomass in both gardens. There was no significant difference between the introduced plants and those from the presumed native Japanese populations in terms of most characteristics. Interestingly, plants from China were taller and had fewer ramets than those from Japan, North America, and Europe, highlighting the broader differences within the native range of this species.

Both the introduced North American and European populations exhibited greater plasticity in terms of the number of ramets compared to the native Chinese populations. In addition, the plasticity in number of ramets were also higher in introduced North American and European populations compared to that of their putative source Japanese populations, suggesting an evolutionary shift towards increased clonality in the introduced ranges.

The findings indicated that the invasion success of R. japonica may be attributed to the introduction of a highly clonal genotype (general-purpose genotype) from Japan, and a build on post-introduction evolutionary shift of higher clonality.

“Our research demonstrates that introduction of certain genotype and an evolutionary shift towards greater plasticity in clonality, could have contributed to the large-scale colonization of R. japonica in new environments. It provides a good example for investigating mechanisms behind the phenotypic divergence of invasive plants across large biogeographic distribution,” said Dr. LIAO Zhiyong, a correspondence author of the study. 

A photo of Reynoutria japonica population in the introduced range Europe. 

(Image by Dr. Madalin Parepa.)

An overview of the common garden of Reynoutria japonica at XTBG in May 2022.  (Image by LIAO Zhiyong)

First Published: 19 February 2025