The Japanese knotweed invasion viewed as a vast unintentional hybridisation experiment

Abstract

Chromosome counts of plants grown from open-pollinated seed from Japanese knotweed around the world have revealed the presence of extensive hybridisation with both native and other introduced taxa. These hybrids fit into three categories: interand intraspecific hybrids involving the taxa of Fallopia section Reynoutria (giant knotweeds), hybrids between Japanese knotweed and F. baldschuanica (Regel) Holub and hybrids between Japanese knotweed and the Australasian endemics of the genus Muehlenbeckia. In this minireview, the viability of the different classes of hybrid and the potential threats they pose are discussed in the context of recent examples of allopolyploid speciation, which generally involve hybridisation between a native and an alien species. Such wide hybridisations also challenge accepted taxonomic classifications. Japanese knotweed s.l. provides a fascinating example of the interplay between ploidy level, hybridisation and alien plant invasion. The octoploid (2n ¼ 88) Fallopia japonica var. japonica (Houtt.) Ronse Decraene is a single female clone throughout much of its adventive range, and provides an ideal system for investigating the potential for wide hybridisation.

Hybridisation is associated with increased fecundity and size in invasive taxa: meta‐analytic support for the hybridisation‐invasion hypothesis

“…Invasive populations of hybrid Myriophyllum , Reynoutria and Typha can reproduce clonally, have been shown to be largely composed of F 1 individuals (Kirk et al . ; Bailey ; LaRue et al . ), and in our analyses were all significantly larger than their parents (Fig.…”

“…Many invasive plants reproduce primarily via clonal spread (Py sek & Richardson 2007); and indeed clonality has been identified as an important mechanism by which heterosis achieved in the F 1 (which is normally broken down by recombination in sexual species) can be stabilised in hybrid lineages, potentially increasing invasiveness (Ellstrand & Schierenbeck 2000). Invasive populations of hybrid Myriophyllum, Reynoutria and Typha can reproduce clonally, have been shown to be largely composed of F 1 individuals (Kirk et al 2011;Bailey 2013;LaRue et al 2013), and in our analyses were all significantly larger than their parents (Fig. 1c).…”

Novel plant–insect interactions in an urban environment: enemies, protectors, and pollinators of invasive knotweeds

“…has been an important mechanism for spread and hybridization in the United States and Europe (Bailey 2013) and insect communities of these species have been described in their native Japanese range (Kishi et al 2017), to our knowledge no studies have characterized the diversity and relative frequency of insect flower visitors in their North American range. has been an important mechanism for spread and hybridization in the United States and Europe (Bailey 2013) and insect communities of these species have been described in their native Japanese range (Kishi et al 2017), to our knowledge no studies have characterized the diversity and relative frequency of insect flower visitors in their North American range.…”

“…Although sexual reproduction in Fallopia spp. has been an important mechanism for spread and hybridization in the United States and Europe (Bailey 2013) and insect communities of these species have been described in their native Japanese range (Kishi et al 2017), to our knowledge no studies have characterized the diversity and relative frequency of insect flower visitors in their North American range. This initial investigation into the assemblage of flower visitors tests whether native and non-native insects have the potential to facilitate reproduction and hybridization of Fallopia in North America.…”

The influence of invasive Fallopia taxa on resident plant species in two river valleys (southern Poland)

“…Even though the invasion by Fallopia taxa is among the most intensively studied phenomena globally [14,32,33], nevertheless new aspects should be paid attention to and need explanation. More rarely undertaken studies, determining the influence of Fallopia taxa on abiotic and biotic conditions of particular habitats, devote attention to individual taxa from the Fallopia genus.…”