Low genetic variation of invasive Fallopia spp. in their northernmost European distribution range

Knowledge about the reproduction strategies of invasive species is fundamental for effective control. The invasive Fallopia taxa (Japanese knotweed s.l.) reproduce mainly clonally in Europe, and preventing spread of vegetative fragments is the most important control measure. However, high levels of genetic variation within the hybrid F. × bohemica indicate that hybridization and seed dispersal could be important. In Norway in northern Europe, it is assumed that these taxa do not reproduce sexually due to low temperatures in the autumn when the plants are flowering. The main objective of this study was to examine the genetic variation of invasive Fallopia taxa in selected areas in Norway in order to evaluate whether the taxa may reproduce by seeds in their most northerly distribution range in Europe. Fallopia stands from different localities in Norway were analyzed with respect to prevalence of taxa, and genetic variation within and between taxa was studied using amplified fragment length polymorphism (AFLP). Taxonomic identification based on morphology corresponded with identification based on simple sequence repeats (SSR) and DNA ploidy levels (8× F. japonica, 6× F. × bohemica and 4× F. sachalinensis). No genetic variation within F. japonica was detected. All F. × bohemica samples belonged to a single AFLP genotype, but one sample had a different SSR genotype. Two SSR genotypes of F. sachalinensis were also detected. Extremely low genetic variation within the invasive Fallopia taxa indicates that these taxa do not reproduce sexually in the region, suggesting that control efforts can be focused on preventing clonal spread. Climate warming may increase sexual reproduction of invasive Fallopia taxa in northern regions. The hermaphrodite F. × bohemica is a potential pollen source for the male‐sterile parental species. Targeted eradication of the hybrid can therefore reduce the risk of increased sexual reproduction under future warmer climate.     

Herbivore resistance of invasive <Emphasis Type="Italic">Fallopia</Emphasis> species and their hybrids

Hybridization has been proposed as a mechanism by which exotic plants can increase their invasiveness. By generating novel recombinants, hybridization may result in phenotypes that are better adapted to the new environment than their parental species. We experimentally assessed the resistance of five exotic Fallopia taxa, F. japonica var. japonica, F. sachalinensis and F. baldschuanica, the two hybrids F. × bohemica and F. × conollyana, and the common European plants Rumex obtusifolius and Taraxacum officinale to four native European herbivores, the slug Arion lusitanicus, the moth Noctua pronuba, the grasshopper Metrioptera roeselii and the beetle Gastrophysa viridula. Leaf area consumed and relative growth rate of the herbivores differed significantly between the Fallopia taxa and the native species, as well as among the Fallopia taxa, and was partly influenced by interspecific variation in leaf morphology and physiology. Fallopia japonica, the most abundant Fallopia taxon in Europe, showed the highest level of resistance against all herbivores tested. The level of resistance of the hybrids compared to that of their parental species varied depending on hybrid taxon and herbivore species. Genotypes of the hybrid F. × bohemica varied significantly in herbivore resistance, but no evidence was found that hybridization has generated novel recombinants that are inherently better defended against resident herbivores than their parental species, thereby increasing the hybrid’s invasion success. In general, exotic Fallopia taxa showed higher levels of herbivore resistance than the two native plant species, suggesting that both parental and hybrid Fallopia taxa largely escape from herbivory in Europe.     

Landscape dynamics and habitat selection by the alien invasive <Emphasis Type="Italic">Fallopia</Emphasis> (Polygonaceae) in Belgium

Habitat patch colonization dynamics and distribution patterns were analysed at a landscape scale in four invasive Fallopia (Polygonaceae) species. Fallopia sachalinensis and F. aubertii were uncommon and population expansion was not evident during the three consecutive years of study. The two most widespread species, F. japonica and F. × bohemica displayed similar habitat selection patterns with ruderal and natural/semi-natural forests favoured. The highest densities of F. japonica and F. × bohemica individuals were at the edge of preferred habitat patches with different patterns of edge selection. Linear network played an important role in species invasion, with 71% of all F. japonica and F. × bohemica occurring within a 10 m buffer of total linear networks (roads, railways, and rivers). However, the buffer represented only 14.5% of the total landscape surface. The rate of population increase was higher for F. japonica (75.8% and 35.2%, in 2002 and 2003, respectively) than for F. × bohemica (63.6% and 0% in 2002 and 2003, respectively) and was largely the result of intra-patch dynamics with low inter-patch colonization. The total surface area occupied by Fallopia clones in the landscape grew by 34.7% over 2 years of the study, with comparable area growth means for F. japonica and F. × bohemica (34.9% and 34.7%, respectively). The hypothesis that F. × bohemica exhibits higher invasive dynamics due to both clonal and sexual reproduction was not supported by our results.     

Isoenzyme diversity in Reynoutria (Polygonaceae) taxa: escape from sterility by hybridization

The genus Reynoutria is represented by four taxa in the Czech Republic – R. japonica var. japonica and compacta, R. sachalinensis and R. × bohemica. Using isoenzyme analysis, we determined the degree of genotype variability in all taxa and compared clones of R. japonica var. japonica from the Czech Republic with those from Great Britain. While the rarely occurring tetraploid variety R. japonica var. compacta possesses low variability, the octoploid female clone of R. japonica var. japonica is genetically uniform in the 93 clones sampled and belongs to the same genotype that is present in the whole Europe. R. japonica var. japonica can be fertilized by the pollen of tetraploid R. sachalinensis and a hexaploid hybrid R. × bohemica is produced. In R. sachalinensis, 16 genotypes were found in the 50 clones sampled. R. × bohemica is genetically the most diverse taxon in the study area, with 33 genotypes recorded among 88 clones sampled.     

Variation of growth and functional traits of invasive knotweeds (<Emphasis Type="Italic">Fallopia</Emphasis> spp.) in Belgium

Three invasive Fallopia taxa are present in Belgium: F. japonica (FJ), F. sachalinensis (FS) and their hybrid F. × bohemica (FB). FS is the least invasive of the three taxa. In this study, we compared the taxa, in sites where they co-occur, for differences in functional traits that might influence their competitive ability and invasiveness—shoot height and ramification, leaf size, specific leaf area (SLA) and foliar nitrogen (N) concentration. The three taxa exhibited similar growth kinetics and similar SLA. However, FS differed in its architecture and allocation of leaf area, having less ramified shoots and a steeper gradient of decreasing leaf size along the main shoot. Also, FS had greater foliar N and less efficient N resorption from senescing leaves. These traits values may result in lower competitive ability of FS for light and nitrogen. For the same traits, FB was generally intermediate between FS and FJ, but often closer to the latter. FB was more variable than FS and FJ, possibly due to larger genetic variation. SLA and ramification varied greatly amongst sites for all taxa, due in part to plastic response to contrasting light regimes. Variation in functional traits values may in part explain the variation in invasiveness amongst the members of the Fallopia complex in Belgium.     

Invasiveness Does Not Predict Impact: Response of Native Land Snail Communities to Plant Invasions in Riparian Habitats

Studies of plant invasions rarely address impacts on molluscs. By comparing pairs of invaded and corresponding uninvaded plots in 96 sites in floodplain forests, we examined effects of four invasive alien plants (Impatiens glandulifera, Fallopia japonica, F. sachalinensis, and F.×bohemica) in the Czech Republic on communities of land snails. The richness and abundance of living land snail species were recorded separately for all species, rare species listed on the national Red List, and small species with shell size below 5 mm. The significant impacts ranged from 16–48% reduction in snail species numbers, and 29–90% reduction in abundance. Small species were especially prone to reduction in species richness by all four invasive plant taxa. Rare snails were also negatively impacted by all plant invaders, both in terms of species richness or abundance. Overall, the impacts on snails were invader-specific, differing among plant taxa. The strong effect of I. glandulifera could be related to the post-invasion decrease in abundance of tall nitrophilous native plant species that are a nutrient-rich food source for snails in riparian habitats. Fallopia sachalinensis had the strongest negative impact of the three knotweeds, which reflects differences in their canopy structure, microhabitat humidity and litter decomposition. The ranking of Fallopia taxa according to the strength of impacts on snail communities differs from ranking by their invasiveness, known from previous studies. This indicates that invasiveness does not simply translate to impacts of invasion and needs to be borne in mind by conservation and management authorities.     

Extreme differences in population structure and genetic diversity for three invasive congeners: knotweeds in western North America

Japanese, giant, and the hybrid Bohemian knotweeds (Fallopia japonica, F. sachalinensis and F. × bohemica) have invaded the western USA and Canada, as well as other regions of the world. The distribution of these taxa in western North America, and their mode of invasion, is relatively unresolved. Using amplified fragment length polymorphisms of 858 plants from 131 populations from British Columbia to California to South Dakota, we determined that Bohemian knotweed was the most common taxon (71 % of all plants). This result is in contrast to earlier reports of F. × bohemica being uncommon or non-existent in the USA, and also differs from the European invasion where it is rarer. Japanese knotweed was monotypic, while giant knotweed and Bohemian knotweed were genetically diverse. Our genetic data suggest that Japanese knotweed in western North America spreads exclusively by vegetative reproduction. Giant knotweed populations were mostly monotypic, with most containing distinct genotypes, suggesting local spread by vegetative propagules, whereas Bohemian knotweed spreads by both seed and vegetative propagules, over both long and short distances. The high relative abundance and genetic diversity of Bohemian knotweed make it a priority for control in North America.     

Effects of climatic factors on Fallopia japonica s.l. seedling establishment: evidence from laboratory experiments

The highly invasive Fallopia complex (Fallopia japonica s.l., Fallopia japonica var. japonica, Fallopia sachalinensis and the hybrid Fallopia × bohemica) is known to spread primarily vegetatively by rhizomes and stem fragments in its adventive range. Sexual reproduction has rarely been shown in Europe, despite a high production of germinable seeds. To elucidate this contradiction the aim of the present study was to determine which environmental conditions prevent seed germination or seedling establishment. Several laboratory experiments were conducted focusing on water and light supply as well as the influence of frost. According to morphological and cytological analyses of the parental plants paired with morphological analyses of the seedlings, the seeds used for these experiments were assumed to belong predominantly to the hybrid Fallopia × bohemica. Laboratory experiments revealed that seedling establishment is hampered by severe drought or strong late frost, which are, however, rare events in the study region and could not be crucial in explaining the rarity of seedlings in the field. We discuss the possible role of weather conditions that might lead to a loss of seeds or seedlings under field conditions and include a comparison of several other cited studies carried out in the adventive range of Fallopia japonica s.l. that observed either the presence or the absence of Fallopia seedlings in the field.     

Reynoutria niche modelling and protected area prioritization for restoration and protection from invasion: A Southeastern Europe case study

An important step in managing invasive species is determining the factors responsible for their current and potential distribution, especially when species distribution is climatically determined like in Reynoutria taxa case. The main aim of this paper was to integrate all available distribution data of the Reynoutria taxa in SE Europe and to predict in which habitats and along which corridors its future spread can be expected. Distribution data of the Reynoutria taxa were obtained from extensive field studies in the period from 2006 to 2016, as well as from the literature and herbarium sources. A total of 4081 localities in Serbia and the Kosovo region, Montenegro, Slovenia, Croatia, Bosnia and Herzegovina, Bulgaria and Romania have been recorded, most frequently in riparian and human-made habitats. Ecologically suitable ranges for the Reynoutria taxa were predicted using the MaxEnt program and 19 bioclimatic variables which were derived from the WorldClim data set. Results of this study showed that the most frequent Reynoutria taxa in SE Europe are R. japonica var. japonica and hybrid R. × bohemica. The most suitable geographical areas for R. japonica and R. sachalinensis are mostly located in the north, while for R. × bohemica the central part of SE Europe is suitable. The precipitation of the warmest quarter had a high influence on the potential distribution modelling of these closely related species. Potential distribution modelling revealed R. × bohemica’s high temperature tolerance in different seasons with high durability of drought (up to 60 mm per year less precipitation than parental species). Moreover, this research predicts which areas are most likely to be invaded, and makes suggestions where to focus management efforts for survey and removal of these invaders, especially in protected areas. According to the future climate analysis R. japonica and R. × bohemica could expand their range in riparian habitats up to 30–40%. Consequently, invasion in Slovenia’s and Croatia’s rivers requires urgent preventative measures. This study provides empirical evidence that these plants could become widespread throughout SE Europe within 25 years under the current trend and emphasizes that regionally specific management plans should be implemented to prevent further spread of these taxa.     

Haplotypes of <Emphasis Type="Italic">Fallopia</Emphasis> introduced into the US

In the US, clonal growth of Fallopia japonica, Fallopia sachalinensis and their hybrid Fallopia x bohemica (Polygonaceae) is prominent, yet sexual reproduction and hybridization contribute to the genetic complexity of swarms. The contribution to this diversity from multiple introductions is unknown. Using 800 bp of the non-coding chloroplast marker accD–rbcL, we compared 21 Japanese haplotypes with 46 US samples from 11 states, 2 Canadian samples, and 6 European samples from 4 countries, in order to investigate if there were repeated introductions from Asia. While most North American and all European haplotypes accessions in our collection matched a single widespread haplotype, we identified 8 other haplotypes. Three haplotypes of F. japonica (including the widespread haplotype) and one F. sachalinensis matched previously identified Japanese haplotypes, supporting the hypothesis of multiple introductions in the US. Five additional US haplotypes were detected once. Four of these differed from Japanese haplotypes by one single nucleotide polymorphism (SNP), possibly indicating a recent in situ change. The fifth haplotype represents a garden cultivar, which differed from all F. japonica haplotypes. It therefore appears that the US genetic diversity of these taxa has three sources: intra-specific reproduction, inter-specific reproduction, and multiple sources of introduction.     

Genetic diversity of a relict plant species, Ligularia sibirica (L.) Cass. (Asteraceae)

Rare plant species can be divided into naturally, ‘old rare’ species and anthropogenically, ‘new rare’ species. Many recent studies explored genetic diversity of ‘new rare’ species. Less is, however, known about genetic diversity of ‘old rare’ species. We examined isozyme genetic variability of 20 populations of an ‘old rare’ plant species, Ligularia sibirica (Asteraceae) in the Czech and Slovak Republic. It is a long-lived perennial herb with mixed-mating breeding system, widely distributed from East Asia to European Russia, with few isolated relict populations in the remaining part of Europe.The results showed high genetic diversity within populations (80.8%) and a low level of genetic differentiation (F_ST = 0.179). Genetic distance between populations correlated significantly with geographic distance. There was also a significant positive correlation between genetic diversity and population size. This is probably caused by destruction of habitats in last centuries and subsequent decrease of population size. Patterns of genetic diversity suggest that the recent distribution is a result of stepwise postglacial migration of the species and subsequent natural fragmentation.We conclude that L. sibirica populations preserve high levels of genetic diversity and are not yet threatened by genetic factors. However, this may change if changes in habitat conditions continue.     

Facilitation in multiple life-history stages: evidence for nucleated succession in coastal dunes

Garden experiments focused on vegetative regeneration were carried out with four invasive taxa of the genus Reynoutria (R. japonica var. japonica, R. japonica var. compacta, R. sachalinensis and a hybrid between R. sachalinensis and R. japonica var. japonica, R. ×bohemica). Regeneration ability of stems and rhizomes, timing of shoot emergence and biomass production were studied under the following treatments: laid horizontally on the soil surface; placed upright; buried in the soil; floating in water. Two different soils (sand and garden loam) representing contrasting nutrient levels were applied. Differences were found in the capability and speed of regeneration, as well as in the quality of shoots produced. Regeneration from stems was less efficient than that from rhizomes in all taxa except R. sachalinensis. R. ×bohemica exhibits higher regeneration potential (61%) than all other taxa and can be considered as the most successful taxon of the Czech representatives of the genus Reynoutria in terms of regeneration and establishment of new shoots. High regeneration capacity was also exhibited by R. japonica var. compacta (52%). Other taxa showed generally lower regeneration rates (R. japonica var. japonica 39% and R. sachalinensis 21%), but under some treatments the percentage of regenerated segments was high, too. R. japonica var. japonica rhizomes regenerated successfully in all three soil treatments but not in the water. An opposite pattern was found for its stems: they regenerated well if exposed to water treatment but in the soil, they did not regenerate at all. Particular taxa responded to the soil type in a contrasting way. R. sachalinensis and R. ×bohemica regenerated better in loam while the opposite was true in R. japonica var. japonica. R. japonica var. compacta produced the tallest and R. ×bohemica the heaviest and most robust shoots. It is concluded that rhizomes are more crucial than stems for the spread of knotweeds through fragmentation and clonal growth, suggesting the importance of soil disturbance.     

Asexual spread versus sexual reproduction and evolution in Japanese Knotweed s.l. sets the stage for the “Battle of the Clones”

The invasion of NW Europe by a single clone of male-sterile Fallopia japonica var. japonica by purely vegetative reproduction has demonstrated that reproduction by seed and the genetic diversity associated with it may not be an essential feature of plant invasions, at least in the short term. What is less well known is that a significant proportion of the Japanese Knotweed s.l. involved is not F. japonica var. japonica, but the hybrid between it and F. sachalinensis–F. × bohemica. This hybrid is able to backcross to either parent with the potential to replace the missing male F. japonica; by the same process, the hybrid is generating the genetic diversity so conspicuously lacking in F. japonica. In terms of understanding the population structure in a particular country, it is important to be able to identify hybrids and putative back-crosses. We bring together a mixture of published and unpublished information to provide a comprehensive section on morphological and anatomical aids to identification. Regeneration of plants from stem and rhizome fragments varies by taxon, as do responses to control techniques, underlining the importance of correct identification of these plants. In this paper we look closely at this group of taxa, with special emphasis on the role played by hybridization, with an examination of the genetic make up of seedlings produced in the wild or by artificial hybridizations, and the implications that this will have on the future directions of the invasion process.     

The potential role of polyploidy and hybridisation in the further evolution of the highly invasive <Emphasis Type="Italic">Fallopia</Emphasis> taxa in Europe

Japanese knotweed s.l. comprises Fallopia japonica, F. sachalinensis, F. × bohemica and any F2s or backcrosses. The parental taxa were introduced from the East to the West as garden ornamentals in the nineteenth century, and soon spread beyond the confines of the garden to become widespread and persistent weeds. Since only female F. japonica var. japonica was introduced, its impressive spread has occurred solely by vegetative means. However, the initial lack of genetic variability has been complemented by an extensive series of hybridisations in the adventive range. We examine the history, spread, reproductive biology and ecological impact of these species in the West. The role and importance of polyploidy and hybridisation in their invasion of the West is discussed, as are the implications of these factors for the potential further evolution of the group.     

Occupational strategy of runner reed (Phragmites japonica): Change of growth patterns with developmental aging

The characteristics of P. japonica stands growing along ten transect in an AFP were assessed. Especially those of the reproductive organs in terms of developmental stages were focused. Four consecutive stages were observed based on the existence of reproductive organs (flowers and stolons). Plants in the ‘stolon’ and ‘flower and stolon’ stages played a role as a colonizer by stolonization (the longest length of stolon was more than 9 m) while those in the ‘flower’ stage played a role as an occupant via forming tall and dense shoots on tussocks (more than 2 m and about 20 shoots per tussock including dead standing shoots). Consecutive developmental stages according to changes in growth patterns, particularly in the conversion of reproductive organ from asexual (stolon) to sexual (flower), was the critical strategy of P. japonica for efficient monotypic occupation. This occupational strategy of P. japonica also resulted in a sharp decrease of the plant species richness (two to three including P. japonica) growing in the same area with P. japonica in the mature (‘flower’) stage.     

Assessing genetic diversity of populations of topmouth culter (Culter alburnus) in China using AFLP markers

Genetic diversity of five wild populations and a cultured population of topmouth culter (Culter alburnus) was investigated using amplified fragment length polymorphism (AFLP). A total of 373 reproducible bands amplified with seven AFLP primer combinations were obtained from 163 fish. The percentage of polymorphic loci ranged widely from 37.0% to 69.2% within distinct populations. The cultured population appeared to have a lower level of polymorphism (37.0%), gene diversity (0.121 ± 0.188) and Shannon's Information index (0.183 ± 0.263) than the wild populations. Analysis of molecular variance (AMOVA) revealed that average F_ST value overall loci was 0.2671, and the percentage of variation within population (73.29%) was larger than among populations (26.71%) (P < 0.01). The six populations were clustered into two major clades with UPGMA. The results from analysis of population pairwise gene flow indicated moderate gene flow among populations. Our study indicated that the genetic diversity of the cultured population was reduced compared with the wild populations. Geographic isolation, habitat, and artificial selection all may have played important roles in population differentiation. The information may be beneficial to future broodstock selection and defining conservation management for the different populations of topmouth culter.     

Morphological and chromosomal variation in Fallopia section Reynoutria (Polygonaceae) in Korea

We have examined morphological and chromosomal variation inFallopia sect.Reynoutria in Korea to clarify their taxonomic identities and to determine whether their morphological variability is associated with ploidy levels. Principal components analysis (PCA) of individuals from 21 populations, using major distinguishing characters, revealed the presence of four major entiries of sect.Reynoutria in Korea; these includeF. sachalinensis, F. japonica var.japonica, F. forbesii, and the Nonsan population consisting of presumed hybrids. Based on morphology, it is hypothesized that the Nonsan population was probably derived from multiple hybridization events involving the three named taxa. The results also indicate thatF. forbesii is distinct fromF. japonica var.japonica. Polyploidy is more prevalent in sect.Reynoutria than has been previously recognized.Fallopia sachalinensis in Korea occurs as dodecaploids with 2n=132; our count is the first dodecaploid count for the species, and represents the highest chromosome number known in the genus.Fallopia japonica var.japonica occurs as tetraploids (2n=44), hexaploids (2n=66), and octoploids (2n=88), whileF. forbesii occurs as hexaploids (2n=66) and octoploids (2n=88); our counts appear to be the first reported chromosome numbers forF. forbesii. Morphological analysis indicates that there is no apparent correlation between the ploidy levels in these taxa and the morphological characters that we have considered in this study except that the tetraploids ofF. japonica var.japonica tend to have somewhat thicker leaves.     

Population structure and genetic diversity of the threatened quillwort Isoëtes malinverniana and implication for conservation

The goal of this research was to investigate genetic variation in Isoëtes malinverniana (Isoëtaceae) to select candidate populations for future conservation efforts. To this aim, ISSR and AFLP analyses, carried out using six and four primer combinations, respectively, produced a total of 425 bands, 97.18% of which were polymorphic.Our results suggest that I. malinverniana shows medium to high genetic diversity (mean Nei's genetic diversity: H = 0.1491 for ISSR data; H = 0.2289 for AFLP data) and a substantial amount of gene flow between the analysed populations (N_m = 1.768, with combined ISSR and AFLP data). The moderate levels of population differentiation support the hypothesis that the fragmentation and isolation of I. malinverniana occurred only recently, probably due to the intensive agriculture practice and water pollution.These results will be used to focus further studies aimed at supporting reintroduction programs within suitable sites of the distribution area.     

Genetic diversity of Aegiceras corniculatum (Myrsinaceae) revealed by amplified fragment length polymorphism (AFLP)

Aegiceras corniculatum is a cryptoviviparous mangrove tree distributed in the Indo-West Pacific. The genetic structure of 13 populations of A. corniculatum from South China, Malay Peninsula, Sri Lanka, and North Australia, was assessed by amplified fragment length polymorphism (AFLP) markers. Our results showed a relatively high level of genetic variation at the species level (P = 92%, H_E = 0.294 and H_s = 0.331 ± 0.001). The value of G_ST was 0.698, suggesting significant genetic differentiation among populations. At the population level, however, genetic diversity was low (P = 24%, H_E = 0.086 and H_s = 0.127 ± 0.001). When populations were grouped according to geographic regions, i.e., South China, Malay Peninsula and Sri Lanka, it was inferred from analysis of molecular variance (AMOVA) that about half the total variation (49%) was accounted for differentiation between regions. A UPGMA dendrogram based on genetic distance also revealed five major clades corresponding to geographical regions within the distribution of A. corniculatum, although the precise relationships among the clades were not fully concordant with expected geographical delineations and need further study.     

How does Reynoutria invasion fit the various theories of invasibility?

Questions: 1. How does species richness of recipient communities affect Reynoutria invasion? 2. How does Reynoutria invasion change host community structure? 3. Are there any differences in habitat preferences among three closely related Reynoutria taxa? 4. How does the genetic structure of Reynoutria populations change along the course of a river? Location: River Jizera basin, north Bohemia, Czech Republic. Methods: Nine 0.25 km² plots were chosen along the river. Within each plot all main habitat types were determined and sampled using the Braun‐Blanquet scale to determine the invasibility of various communities. The patches invaded by Reynoutria taxa and surrounding Reynoutria‐free vegetation in the same habitat type were sampled as relevé pairs to compare the composition of invaded and non‐invaded vegetation. In addition, to characterize the genetic structure of Reynoutria populations along the river, 30 samples from different clones were collected. Results and conclusions: 1. The species richness of communities has no influence on the success of Reynoutria invasion in the area studied. The combination of environmental conditions and propagule spread is more important to the invasion success than the number of species in the host community. 2. Reynoutria invasion greatly reduces species diversity. 3. R. japonica invaded more habitat types than R. sachalinensis and R.×bohemica. The hybrid R.×bohemica outcompetes the parental taxa at sites where both taxa co‐occur. 4. Isozyme analysis revealed phenotype variability in the hybrid in contrast to the parental taxa. Different hybrid phenotypes are distributed randomly on the middle and lower reaches of the River Jizera; one of them dominates and the other three occur occasionally. This pattern supports the hypothesis that sexual reproduction occasionally occurs within Reynoutria taxa.