Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Fallopia x bohemica



Fallopia x bohemica


  • Last modified
  • 01 November 2019
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Fallopia x bohemica
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • It is generally an under-recorded component of the knotweed populations. It occupies the same sorts of habitat as Japanese knotweed (F. japonica) does in its adventive range. There is some evidence that it is mor...

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Fallopia x bohemica; male fertile F. x bohemica plant.
TitleFlowering plant
CaptionFallopia x bohemica; male fertile F. x bohemica plant.
Copyright©John P. Bailey
Fallopia x bohemica; male fertile F. x bohemica plant.
Flowering plantFallopia x bohemica; male fertile F. x bohemica plant.©John P. Bailey
Fallopia x bohemica; male fertile F. x bohemica plant
TitleFlowering plant
CaptionFallopia x bohemica; male fertile F. x bohemica plant
Copyright©John P. Bailey
Fallopia x bohemica; male fertile F. x bohemica plant
Flowering plantFallopia x bohemica; male fertile F. x bohemica plant©John P. Bailey
Fallopia x bohemica; close-up of flowers on a fertile male F. x bohemica plant.
TitleFlowers and foliage
CaptionFallopia x bohemica; close-up of flowers on a fertile male F. x bohemica plant.
Copyright©John P. Bailey
Fallopia x bohemica; close-up of flowers on a fertile male F. x bohemica plant.
Flowers and foliageFallopia x bohemica; close-up of flowers on a fertile male F. x bohemica plant.©John P. Bailey
Comparison of Fallopia leaves; (a) Fallopia sachalinensis. (b) Fallopia x Bohemica. (c) Fallopia japonica var. japonica.
CaptionComparison of Fallopia leaves; (a) Fallopia sachalinensis. (b) Fallopia x Bohemica. (c) Fallopia japonica var. japonica.
Copyright©John P. Bailey
Comparison of Fallopia leaves; (a) Fallopia sachalinensis. (b) Fallopia x Bohemica. (c) Fallopia japonica var. japonica.
LeavesComparison of Fallopia leaves; (a) Fallopia sachalinensis. (b) Fallopia x Bohemica. (c) Fallopia japonica var. japonica.©John P. Bailey


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Preferred Scientific Name

  • Fallopia x bohemica (J. Chrtek & A. Chrtková) J. P. Bailey

Other Scientific Names

  • Polygonum x bohemicum (J. Chrtek & A. Chrtková) P.F. Zika & A.L. Jacobson
  • Reynoutria x bohemica J. Chrtek & A. Chrtková

International Common Names

  • English: bohemian knotweed; hybrid knotweed

Local Common Names

  • Poland: rdest posredni; rdestowiec posredni
  • Sweden: hybridslide

Summary of Invasiveness

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It is generally an under-recorded component of the knotweed populations. It occupies the same sorts of habitat as Japanese knotweed (F. japonica) does in its adventive range. There is some evidence that it is more difficult to control than its parents (Bimova et al., 2003) and that it can exploit a wider range of habitat than its parents (Bailey and Wisskirchen, 2006). Some clones cover very large areas.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Polygonales
  •                         Family: Polygonaceae
  •                             Genus: Fallopia
  •                                 Species: Fallopia x bohemica

Notes on Taxonomy and Nomenclature

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Fallopia x bohemica (Chrtek & Chrtková) J.P. Bailey (Stace, 1989) is the hybrid between Fallopia japonica and Fallopia sachalinensis and occurs at three different ploidy levels: 2n=44; 66; and 88. Although most literature nowadays refers to it under the Fallopia combination, older papers refer to Reynoutria x bohemica Chrtek & Chrtková, and the Americans have even published the Polygonum combination; Polygonum x bohemicum (Zika and Jacobson, 2003). There are two reasons behind this generic plentitude. Firstly, Japanese knotweed [Fallopia japonica] was described twice independently, the first name Reynoutria japonica being lost for more than 100 years, and in the mean time it was described again as Polygonum cuspidatum (Bailey and Stace, 1992). However, many taxonomists now accord generic status to the former sections of the Linnaean genus Polygonum. Fallopia and Reynoutria were then the correct names for the genera containing the climbers and the Japanese knotweeds, respectively. In the 1980s, morphological and hybridization studies indicated that these two genera should be merged under Fallopia, the older name (Ronse Decraene and Akeroyd, 1988; Bailey and Stace, 1992). A recent molecular study by Galsasso et al. (2009) proposes the transfer back to Reynoutria and The Plant List (2013) gives Reynoutria x bohemica Chrtek & Chrková as the preferred name. 

It is questionable whether a vernacular name is needed in the first place because it is mainly the concern of specialists. The term Japanese knotweed s.l. is the author’s preferred name, which covers the whole spectrum of what may be found. It is called bohemian knotweed in the USA, but the latest ‘British Flora’ (Stace, 2001) does not provide a common name. Botta-Dukát and Balogh (2008) additionally offer the name hybrid knotweed.
Although artificial hybrids were produced in Leicester in 1982, F. x bohemica was first described from the Czech Republic by Chrtek and Chrtková (1983) – hence the specific name x bohemica. The name Reynoutria x vivax is also in the literature (Schmitz and Strank, 1985), but this was illegitimate, applied to the wrong taxon and was in any case predated by the Czech authors. It was not reported from Japan until much later in 1997, as Reynoutria x mizushimae Yokouchi ex T. Shimizu (Bailey, 2003).



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It has the same general growth form as F. japonica var. japonica, but the leaves are much larger and do not have the truncate bases so typical of F. japonica. Unlike F. japonica var. japonica, both sexes are found, and in the UK at least, the hermaphrodites seem to outnumber the male-sterile plants. Clones extend by rhizome growth and may occupy considerable areas.

Inflorescences are similar to those of either of the parents. Florets are 1-2.5 mm long and functionally unisexual but with each male or female flower possessing the complementary but vestigial, organs of the other sex. Each floret has 5 petals and 8 stamens (Gillespie and Faithfull, 2004).

A tall herbaceous, rhizomatous perennial with stems up to 3.5 m tall. Leaf blades of lower cauline leaves up to 25 x 17 cm (length:breadth ratio - 1.3:1.6), ovate with cuspidate apex and cordate to subcordate base. Distinctive intermediate trichomes on the lower leaf epidermis are the best character for distinguishing it from its parents (see Bailey et al., 1996; Bailey and Wisskirchen, 2008; Zika and Jacobson, 2003 for illustrated details).


Plant Type

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Seed propagated
Vegetatively propagated


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Bailey et al. (1996) give detailed information about the distribution in the British Isles with six figure grid references; more up to date data on a 10 km square basis is to be found in Preston et al. (2002).

The known European distribution is mapped in Bailey and Wisskirchen (2006), with appendices containing detailed localities for Germany and France. Since then, more information has come to light on the occurrence in and around Milan, Northern Italy (Padula et al., 2008), and specimens have also been identified from Serbia (Belgrade) (J Bailey, University of Leicester, UK, personal observation, 2009), where it is invasive, and where F. x bohemica is said to be more common than F. japonica (M Glavendekic, University of Belgrade, Serbia, personal communication, 2009). It is present and invasive in Bulgaria (J Bailey, University of Leicester, UK, personal observation, 2009).
Tiébré et al. (2007) give some details of the Belgian populations. There has been a great deal of research from the Czech Republic; maps and comprehensive lists of localities (Mandák et al., 2004). Eliás (2001) reports the plant from Slovakia, but lacks details of localities. Botta-Dukat and Balogh (2008) confirm its presence in Romania and Ukraine. The Scandinavian distribution is covered by 'Flora Nordica' (Jonsell and Karlsson, 2000), and further details for Norway are to be found in Fremsted and Elven (1997). It also occurs in Switzerland (O Bossdorf, University of Bern, Switzerland, personal communication, 2009).
There are still many notable omissions in Europe. No records are known from Austria, Latvia, Lithuania, Estonia, former Yugoslavia (apart from Serbia), Albania, Belarus or Russia. However, there would appear to be no reason why it should not occur anywhere within the range of F. japonica as mapped by Jalas and Suominen (1979), particularly when taking into account the increasing predominance of F. x bohemica in knotweed populations as you get further east. Incidentally, it should be noted that F. x bohemica extends further south than the Jalas and Suominen map suggests, in both France and Italy. The Italian plants are not strictly in the Mediterranean climate (due to latitude or altitude), whereas the French ones most certainly are, although it is not known whether this extension of range beyond that of its parents is stochastic or the result of heterosis.
The plant is widespread in the USA and Canada, but is commonly misidentified as one of its parents; in some areas it is a major component of the knotweed populations. Gammon et al. (2007) reported that the parents are sympatric in 28 states in the USA. However, with vegetative spread, this is no prerequisite for the occurrence of the hybrid. The USDA website map for ‘Polygonum x bohemicum’ indicates that it is absent from the USA, but present in British Columbia, Ontario and Quebec. A more comprehensive distribution is shown on the website where ‘F. x bohemica’ is found in the following states of America: Washington, Oregon, Idaho, Minnesota, Iowa, Nebraska, Kansas, Illinois, Tennessee, Louisiana, North Carolina, Virginia, West Virginia, Pennsylvania, Maryland, New York, New Hampshire and Massachusetts. However, the origin and accuracy of these data are unknown.
There have been no reports from Africa, India or South America, although the recent discovery of F. japonica in Chile implies it could occur in South America.
In Australasia, it is known from a suburb of Sydney, Australia (Conolly, 1998, 2001; Bailey and Wisskirchen, 2006).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes


JapanPresentBailey, 2003Recently discovered

North America

CanadaPresentPresent based on regional distribution.
-British ColumbiaPresent Invasive USDA-NRCS, 2008
-OntarioPresent Invasive USDA-NRCS, 2008
-QuebecPresent Invasive USDA-NRCS, 2008
USAPresentPresent based on regional distribution.
-ConnecticutPresent Invasive Gammon et al., 2007
-IdahoPresenteFloras, 2008
-IllinoisPresenteFloras, 2008
-IowaPresenteFloras, 2008
-KansasPresenteFloras, 2008
-LouisianaPresenteFloras, 2008
-MainePresent Invasive Gammon et al., 2007
-MarylandPresenteFloras, 2008
-MassachusettsPresent Invasive Gammon et al., 2007
-MinnesotaPresenteFloras, 2008
-NebraskaPresenteFloras, 2008
-New HampshirePresenteFloras, 2008
-New YorkPresent Invasive eFloras, 2008
-North CarolinaPresenteFloras, 2008
-OregonPresenteFloras, 2008
-PennsylvaniaPresenteFloras, 2008
-Rhode IslandPresent Invasive Gammon et al., 2007
-TennesseePresenteFloras, 2008
-VermontPresent Invasive Gammon et al., 2007
-VirginiaPresenteFloras, 2008
-WashingtonPresent Invasive eFloras, 2008
-West VirginiaPresenteFloras, 2008


AustriaPresentEPPO, 2014
BelgiumWidespread Invasive Meerts and Tiebre, 2007
CroatiaPresentEPPO, 2014
CyprusPresentEPPO, 2014
Czech RepublicPresent Invasive Mandák et al., 2004; Mandák et al., 2004; EPPO, 2014Very extensive and spreading
DenmarkPresent Invasive Jonsell and Karlsson, 2000; Bailey and Wisskirchen, 2006
FinlandPresentJonsell and Karlsson, 2000; EPPO, 2014Vaasa since late 1960's. Helsinki since 1987
FrancePresent Invasive Bailey and Wisskirchen, 2006; Schnitzler et al., 2007; Schnitzler and Bailey, 2008Some very extensive colonies present
GermanyPresent Invasive Keil and Alberternst, 1995; Bailey and Wisskirchen, 2006; EPPO, 2014Extensive colonies present throughout the country, high densities in the Ruhr
HungaryPresent Invasive Balogh, 1998; Balogh, 2003; Botta-Dukát and Balogh, 2008; EPPO, 2014F. bohemica is more common than F. japonica
IrelandPresent Invasive Bailey et al., 1996; Preston et al., 2002; EPPO, 2014Some long established colonies in the West and in Dublin
ItalyPresent Invasive Bailey and Wisskirchen, 2006; Padula et al., 2008Mainly restricted to Northern Italy
NetherlandsPresentAdolphi, 1999; Bailey and Wisskirchen, 2006; EPPO, 2014
NorwayWidespreadFremsted and Elven, 1997; Jonsell and Karlsson, 2000; Bailey and Wisskirchen, 2006; EPPO, 2014Present in 12 municipalities, some consisting of more than 10 records
PolandWidespread Invasive Fojcik and Tokarska-Guzik, 2000; Bailey and Wisskirchen, 2006; EPPO, 2014
RomaniaPresentBotta-Dukát and Balogh, 2008; EPPO, 2014Mentioned in text, no further details
Russian FederationPresentEPPO, 2014
-Central RussiaPresentEPPO, 2014
SlovakiaWidespreadFehér, 1999; Eliás, 2001Widespread - some large colonies present
SpainPresentEPPO, 2014
SwedenPresentJonsell and Karlsson, 20005 localities reported - first record Uppsala 1975
SwitzerlandPresentBotta-Dukát and Balogh, 2008; EPPO, 2014Ticino and other places - more or less the same frequency as F. japonica (C Krebs, pers. comm.)
UKWidespreadBailey et al., 1996; Preston et al., 2002; EPPO, 2014Widespread with some very large colonies
-Channel IslandsPresent Invasive Bailey et al., 1996; Preston et al., 2002
-England and WalesPresentEPPO, 2014
UkrainePresentBotta-Dukát and Balogh, 2008Presence reported but no further details provided


AustraliaPresentPresent based on regional distribution.
-New South WalesPresent Not invasive Conolly, 1998; Conolly, 2001Sydney

History of Introduction and Spread

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Initially this species was thought to be part of the range of variation of Fallopia japonica var. japonica, and it was only with the application of cytology that it became apparent that there was no morphological variation in the UK F. japonica var. japonica (subsequently shown to be a male-sterile clone) and that the morphologically intermediate plants were actually the hybrid. It was only discovered in the 1980s, therefore its earlier history can only be established by a study of dated herbarium specimens (Bailey and Conolly, 2000). The fact that all F. japonica var. japonica were male-sterile, meant that once male-fertile plants of Fallopia sachalinensis reached Europe, hybridization was inevitable. Any seed collected from Japanese knotweed would thus be of hybrid origin. Botanic gardens around the world were distributing this hybrid seed as F. japonica. Evidence from herbarium material shows that this hybrid arose not long after the arrival of F. sachalinensis in the late nineteenth century (Bailey and Conolly, 2000), whereas the earliest date for a plant established in the wild is currently 1954 for County Durham, UK.

Given that both F. japonica and F. sachalinensis were present in Siebold’s Garden of Acclimatisation in Leiden, it could have also arisen there and been distributed further. However, it is not currently that frequent in the Netherlands, being first reported by Adolphi (1999).
Viable seed is produced in sites where F. japonica var. japonica co-exists with male-fertile F. sachalinensis; however, such sites are rather rare in the UK (Pashley et al., 2003), and germination and establishment are even rarer occurrences. Natural production of F1 seed can in no way account for the current distribution, therefore it must be assumed that it was distributed asexually as a garden plant and subsequently discarded into the wild. Such plants finding themselves on water courses are then able to spread downstream by vegetative means.

Risk of Introduction

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The main method of reproduction is by vegetative propagation so there is a danger of river-borne fragments of rhizome crossing country borders. Also there are some reports of short, sea-borne transfer of viable rhizome fragments of Fallopia japonica from island to island in the west of Scotland (Beerling et al., 1994; Hayward, 2002) and there is nothing to suggest that F. x bohemica is any less adept in this ability so this possibility cannot be excluded. Richards et al. (2008) describe the presence of F. japonica and F. x bohemica in salt marsh habitats in the USA and performed experiments that indicated that both taxa exhibited considerable plasticity in their response to exposure to salt. There is little risk of inadvertent transport to continents not already occupied.

It should be noted that its physiology probably excludes it from warmer climates, because it needs a lot of water during its growing season, and this can of course be supplied by growth next to water courses, as is the case with the populations growing in the Mediterranean region of France (Bailey and Wisskirchen, 2006).


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It occurs in habitats similar to those occupied by Fallopia japonica; principally in riparian and ruderal habitats, but also in salt marshes (Richards et al., 2008).

Habitat List

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Terrestrial – ManagedManaged forests, plantations and orchards Present, no further details
Disturbed areas Principal habitat
Rail / roadsides Principal habitat
Urban / peri-urban areas Principal habitat
Terrestrial ‑ Natural / Semi-naturalRiverbanks Principal habitat Harmful (pest or invasive)
Salt marshes Present, no further details
Rivers / streams Principal habitat Harmful (pest or invasive)

Hosts/Species Affected

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Not usually a problem in cultivated ground.

Biology and Ecology

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It is found in the wild at 3 (4) different ploidy levels: 4x (2n=44); 6x (2n=66); and 8x (2n=88); (10x – 2n=110). The 6x is found everywhere, whereas the 4x is more common in the UK and the 8x in continental Europe. The 6x is the standard F1 hybrid between the European 8x male sterile clone of Fallopia japonica var. japonica and male fertile Fallopia sachalinensis. F1 hybrids originating in this manner will inevitably possess the chloroplast haplotype of the 8x japonica (Hollingsworth et al., 1998, 1999; Pashley et al., 2003). The 6x has very irregular meiosis (Bailey and Stace, 1992), and even though this does not necessarily affect the fecundity of the plant, any offspring is generally aneuploid, apart from those produced by an entirely unreduced gamete. This is how the single USA 10x F. x bohemica is thought to have arisen; by an unreduced pollen grain pollinating an 8x japonica (J Bailey, University of Leicester, UK, personal observation, 2009). The 4x and some of the 8x plants are perfectly fertile. The 4x originates from crosses between the 4x Fallopiajaponica var. compacta and F. sachalinensis and has been made reciprocally at the University of Leicester, UK, and chloroplast haplotype evidence indicates that plants in the wild have also originated from crosses in both directions. The variable fertility in the 8x hybrids points to different origins; the most straightforward is an unreduced sachalinensis gamete fertilizing an 8x japonica. Another possibility is chromosome doubling of a 4x hybrid; this and further options are discussed in Bailey and Wisskirchen (2006).
Reproductive Biology
Like its parents, this is a gynodieocious taxon (hermaphrodite and male-sterile individuals), the hermaphrodites being self-incompatible (Bailey, 1994). The hermaphrodite plants do not make such good female parents even when they have regular meiosis and access to compatible pollen. This seems to be because the development of the gynoecium is not usually so advanced as in the male-sterile plants, although it has been noted that towards the end of the season, some of the hermaphrodite flowers exhibit much greater stigmatal development and do produce seed (Bailey, 1994).
What ever ploidy level is considered, all taxa are capable of producing viable seed giving rise to vigorous plants (usually with aneuploid chromosome numbers), which currently do not become established spontaneously in Europe; the situation in the USA may well be different and is in need of urgent investigation (Forman and Kesseli, 2003; Bailey et al., 2008).
Physiology and Phenology
Flowering begins in mid-August to late September and continues for several weeks or until cut down by frost.


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C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C

Notes on Natural Enemies

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No specific research has been carried out on F. x bohemica because it is rarely found in Japan, but much of what holds for Fallopia japonica might be expected to apply to the hybrid. F. japonica in Japan is attacked by a suite of natural enemies, both arthropod and fungal, not present in its adventive range. To date, 186 species of arthropod and around 40 species of fungus have been recorded from the plant in its native range of Japan (R Shaw, CABI, UK, personal communication, 2008). As a result of this attack, it is not able to compete with local flora as effectively as it does in the introduced range and does not normally reach the same massive size. Of these natural enemies, some exert significant damage such as the chrysomelid beetle Gallerucida nigromaculata, which is described as having potential as a biocontrol agent by Zwoelfer (1973). This is now thought to be Gallerucida bifasciata and not adequately specific. Recent observations by CABI Bioscience show fungal pathogens, as well as arthropods, are significant controlling factors in Japan, across the climatic range of the plant. This includes a number of obligate biotrophic fungi, as well as an ubiquitous leafspot pathogen. In its introduced range, F. japonica is attacked by the green dock beetle, Gastrophysa viridula, but this is only when its normal Rumex host has been consumed and beetle populations are elevated.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Garden waste disposal Yes
Interconnected waterways Yes
Landscape improvement Yes
Ornamental purposes Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Machinery and equipment Yes
Ship ballast water and sediment Yes
Soil, sand and gravelmovement of soil Yes
Water Yes

Impact Summary

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Cultural/amenity Positive and negative
Economic/livelihood Positive
Environment (generally) Negative

Economic Impact

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The economic impact of this species is similar to that of Fallopia japonica in that it is a problem for developers of land infested with F. x bohemica, although it is not entirely clear whether this taxon is actually covered by the letter of the law that proscribes Japanese knotweed (1981 Wildlife and Countryside Act). It is unsightly in amenity areas and a threat to biodiversity along water courses, where, like F. japonica, it is able to spread vegetatively. Control costs will equal, if not exceed, the costs for F. japonica, as there is some evidence (Bimova et al. 2003) that the hybrid is more difficult to eradicate than either parent.

For F. japonica the estimated annual control costs for one county council in Wales, UK, in 1994 was £300,000 (approximately US $600,000). The budget needed to control the 64 ha knotweed infestation in the city and county of Swansea was estimated to be £5.79 million in 1998 (Shaw et al., 2001). To control F. japonica on a national scale in the UK would cost an extrapolated £1.56 billion (approximately US $3 billion) were it to be attempted, as reported by the UK Department of Environment, Food and Rural Affairs in its recent non-native species policy review. An accepted estimate of control costs is £10,000 per hectare for a 3-year spraying regime, with two sprays per year, but this is probably an underestimate if revegetation costs are taken into account. Its presence can add around 10% to the costs of a development project, especially if soil is considered contaminated and subject to additional removal fees. Indeed, a spraying programme on a development site is estimated to be £27.19 per m² (approximately US $54 per m²), and including finance costs this almost doubles to £50.88 per m² (approximately US $100 per m²) if soil has to be removed and clean soil imported and compacted (Child and Wade, 2000).

It is present by roads and railways, and stem debris may impede water flow in smaller water courses.

Environmental Impact

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Impact on Habitats

It can be argued that because its main habitats are ruderal and along water courses, it is unlikely to be a threat to endangered species that are unlikely to occur in such habitats in the first place. Nothing much will eat the plant by choice, nonetheless it provides useful cover for a variety of animals. It is often stated in papers that nothing can grow under the cover of these plants, and there is some evidence of allelopathic interference in addition to the well-known effects of accumulation of stem and leaf debris and light exclusion. However, in suitable areas a vernal understory can be maintained (Gilbert, 1992), the experimental beds of Japanese knotweed s.l. at the University of Leicester, UK are now carpeted with bluebells (Endymion non-scriptus) in the spring, which arose from a few bulbs already present in the soil.
Impact on Biodiversity
There is an interesting case in the Czech Republic with the endangered species Myricaria germanica, which is found in wild mountain rivers with periodical floods each spring, where it grows on the dry shingle. F. x bohemica invades and stabilizes these habitats and completely outcompetes the whole willow-tamarisk shrub community including the M. germanica (K Berchova-Bimova, Czech Academy of Sciences, Czech Republic, personal communication, 2009).

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Myricaria germanicaEN (IUCN red list: Endangered); No details

Social Impact

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As mentioned in the Economic impact section, it may be considered unsightly and intrusive in amenity and other public spaces. In the UK, the constant barrage of publicity in the press (much of it ill-considered i.e. ‘can grow through concrete’) has given members of the public the impression that this is some sort of indestructible Triffid, and that once spotted in a garden it won’t be long before it is found growing up between the floorboards.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Long lived
  • Fast growing
  • Reproduces asexually
  • Has high genetic variability
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Infrastructure damage
  • Modification of hydrology
  • Modification of successional patterns
  • Monoculture formation
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Allelopathic
  • Competition - monopolizing resources
  • Competition - shading
  • Hybridization
  • Rapid growth
Likelihood of entry/control
  • Difficult/costly to control


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Economic Value

Japanese knotweed and its hybrids have and are being considered for use as biomass producers (Callaghan et al., 1984; also see Given that F. x bohemica is a hybrid between Fallopia japonica and Fallopia x sachalinensis, a consideration of the uses of both parents is relevant here. A commercial fungicide is produced from F. sachalinensis; all taxa are a source of resveratrol, although any cultivation for this purpose is unknown. These plants have a long history of use in Chinese traditional medicine and are being actively researched for their active principles. A quick web-search for Polygonum cuspidatum (F. japonica) produced papers looking at the following secondary products of Japanese knotweed: stilbene; kinase inhibitors; phytoestrogens; emodin; and polydatin. Given that F. x bohemica exists at different ploidy levels and with different admixtures of the parental genomes, it is suggested that it could be a valuable source of such biochemicals.
Social Benefit
It could be argued that along waterways, in areas of industrial dereliction, the cheerful green foliage is a pleasant alternative to abandoned supermarket trolleys and windblown carrier bags that often predominate in such areas (Gilbert, 1992). It may also be of value in the remediation of land contaminated by heavy metals etc.

Uses List

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Animal feed, fodder, forage

  • Forage


  • Erosion control or dune stabilization


  • Biofuels

Human food and beverage

  • Emergency (famine) food


  • Chemicals
  • Pesticide


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It is most likely to be mistaken for either of its parents Fallopia japonica and Fallopia sachalinensis. Identification is on the basis of leaf shape and the characteristic intermediate leaf hairs found on the lower epidermis of the leaves. For both of these characters, it is important that only large fully-expanded stem leaves are examined. The male-fertile clones are particularly easy to distinguish from F. japonica var. japonica. Clear characters for distinguishing the three taxa may be found in Bailey et al. (1996, 2008), Zika and Jacobson (2003) and Botta-Dukát and Balogh (2008).

Rapid Response

It is possible to eradicate knotweed if a new infestation of rhizome is spotted quickly and the resultant plants pulled or treated before the roots have become well established.

Public Awareness
Fallopia japonica has a high profile in the media and it is probable that F. x bohemica is considered to be a Japanese knotweed from this point of view. There needs to be more effort spent on distinguishing this taxon from its parents and special efforts should be directed at eradicating male-fertile clones, which could act as pollen parents for further rounds of hybridization.


There has been little success with eradication policies for F. japonica, but given the smaller population size, it is perhaps a realistic and worthwhile aspiration; although there is some evidence that it is more difficult to eradicate (Bimova et al., 2003), and contains greater reserves of genetic diversity than the clone of F. japonica var. japonica. Also see Child (1999), and Child and Wade (2000).

Detection and Inspection

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The UK Environment Agency have produced a Code of Practice, and the Cornwall and Devon Knotweed Forum have produced an excellent guide, which has advice on identifying the plant in the field at various stages of the season.

Similarities to Other Species/Conditions

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As a hybrid between Fallopia japonica and Fallopia sachalinensis it obviously shares many similarities with these plants. It should be noted that the tetraploid F. x bohemica is a cross between the dwarf montane F. japonica var. compacta and F. sachalinensis. The standard 6x and the rarer 8x F. x bohemica are both crosses between the F. japonica var. japonica clone and F. sachalinensis. The tetraploid and octoploid contain half japonica and half sachalinensis chromosomes, whereas the 6x is 66% japonica and 33% sachalinensis. This is reflected in their morphology; although they cannot currently be distinguished morphologically. It is also possible that the montane var. compacta component of the 4x may pre-adapt it to different habitats, because in the wild it is found up to 2500 m.a.s.l. (Bailey, 2003).

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.


F. japonica appears on the UK Wildlife and Countryside Act (1981) and as such it is illegal to cause the plant to grow in the wild. It is listed as a noxious weed in many states and provinces of North America and appears on many weed lists around the world. F. x bohemica is not such a well-recognised taxon, but the same conditions apply to its treatment.

SPS measures

Vehicles should be inspected when moving from infected sites to new ones.


Due to a large and persistent rhizome system, F. japonica is highly resistant to control efforts (Ainsworth et al., 2002), and the same also applies to F. x bohemica. The effectiveness of control and eradication interventions has recently been reviewed thoroughly by Kabat et al. (2006), who included 65 articles in their meta-analysis. Six categories of intervention were included, none of which could eradicate Japanese knotweed or its hybrid in the short term. Cutting treatments alone were not found to result in significant decreases in knotweed abundance. However, statistically-significant reductions in abundance can be achieved by short-term application of: glyphosate; imazapyr; imazapyr and glyphosate; cutting followed by filling stems with glyphosate; and cutting followed by spraying with glyphosate (Kabat et al., 2006). However, these authors were still unable to conclude long-term efficacy for any control measure.

Physical/mechanical control

Mechanical control of F. japonica is difficult, but continual mowing will reduce the resources of the extensive rhizome system if carried out throughout the growing season. Glasshouse trials have shown that repeated cutting at least every 4 weeks and at least 7 weeks prior to senescence, can be effective (Seiger and Merchant, 1997). Pulling up plants complete with root systems can eliminate small stands and is appropriate for local eradication in sensitive areas, but only if carried out continually over a number of years (Baker, 1988). However, digging up roots is even more challenging because they can extend to a depth of 2 m, and 7 m away from the crown, and despite the best efforts, this normally results in an increased stem density. This may be useful for integrated control. With its Fallopia sachalinensis component, F. x bohemica may be slightly more palatable for stock. Certainly F. sachalinensis was promoted as fodder for livestock in the early 1900s (Bailey and Conolly, 2000).

Biological control

Much work has been done on F. japonica at CABI Biosciences (Shaw et al., 2009), but this was mainly based on the European clone of F. japonica, and the aim was to obtain agents specific to that clone. The F. japonica programme has been underway, on behalf of UK and North American sponsors, since May 2003, with two candidate agents, namely a Mycosphaerella leafspot and the psyllid Aphalara itadori. Both of these agents have undergone extensive host range testing and have good potential as biological control agents. Given the difficulty faced by property developers, there would appear to be a market for a mycoherbicide, although registration costs are hindering this approach. As a newly arisen hybrid it is doubtful that any specialist predators actually exist for F. x bohemica and it will be a matter of selecting agents that are restricted to F. japonica and F. sachalinensis.

Chemical control

For F. japonica, chemicals that are permitted on or near water are normally restricted as will be the potential for full control. Child and Wade (2000) recommended five herbicides for F. japonica control, to be applied as foliar sprays. Triclopyr and imazapyr can be applied to young, actively-growing shoots when grasslands need to be protected; glyphosate is suitable during active growth periods when leaves are fully expanded, although larger plants may need to be sprayed using a telescopic/long lance sprayer; picloram can also be used as a soil drench due to its persistence, but not where planting is required within 2 years; and 2,4-D amine is used during the active growing period and as a selective translocated herbicide to be used in grassland, amenity areas and forest situations, although this may depend on which formulation is used in which country. Of the five herbicides, only glyphosate and 2,4-D amine can be used near water. In general, cutting and removing dead stems at the end of the season, prior to a spraying regime the following season, is advisable to aid access. F. japonica is a very resilient plant and unless extremely toxic chemicals are appropriate, repeated well-timed applications should be anticipated, and follow-up spot treatments of any regrowth will often be required.

Stem injection of various herbicides is a relatively modern phenomenon and can produce very good results in some conditions, but concerns remain over the amount of chemical that is actually applied per hectare exceeding statutory maxima. Hagen and Dunwiddie (2008) discovered that using glyphosate, through the injection method, results in the short-term dieback of injected stems. However, drawbacks to its use in certain scenarios should be considered when developing an integrated management plan for knotweed control.

Much of the above will also apply to F. x bohemica, although the larger leaf area and the fact that chemical control is more difficult with F. x bohemica (Bimova et al., 2003), may point to the need for some experimentation with the dosage used and the times and frequency of application.


For F. japonica the use of a combination of mechanical and chemical techniques has proved effective, i.e. cutting and a follow-up spray of new growth, but it is necessary to apply the chemical more than once a season (de Waal, 1995). There are two basic methods: to cut plants to 5 cm height and immediately apply a 25% solution of glyphosate or triclopyr to the cut stems; or cut or mow infestations when the plants reach the early bud stage in the late spring or summer and treat the regrowth in the autumn with glyphosate or triclopyr. If deep digging is used to effectively increase the above ground:below ground biomass ratio, then subsequent chemical application can reduce the time required to achieve effective control (Child et al., 1998). Another herbicide strategy is an integrated strategy with mowing or cutting.

Similar approaches for F. x bohemica should be attempted in order to assess their effectiveness.

Monitoring and Surveillance

There are various GIS surveys on-going in the UK, the first being in Swansea, followed by Cornwall and Devon. Professor Denis Murphy and Daniel Jones at the University of Glamorgan are currently working in this area. Whilst it is highly unlikely that the system would ever be able to discriminate between the different knotweed taxa, it is nevertheless a powerful tool for charting the distribution and extent of this group.


Rapid eradication of F. x bohemica is only possible if rhizome growth has not been too extensive.

Ecosystem Restoration

F. japonica is able to hyper-accumulate heavy metals, including copper, zinc and cadmium, more effectively than other angiosperm species as has been demonstrated in Japan (Nishizono et al., 1989) and Croatia (Hulina and Dumija, 1999). However, the abilities of F. x bohemica in this direction remain untested.

Gaps in Knowledge/Research Needs

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Do the Wildlife and Countryside Act and subsequent Duty of Care regulations actually apply to the hybrid F. x bohemica and if not the appropriate legislative changes should be made?

A comprehensive nation-wide survey of American populations needs to be made, this should also include assessment of the ploidy levels.
Tests of herbicide and potential biocontrol agents should include the complete range of ploidy levels found in the adventive range.
Much viable seed is produced in Europe, but it very rarely establishes in the wild. Research should be carried out to examine what is stopping it and how germination would be affected by the changes in season predicted by the various Climate Change scenarios.
Priority should be given to the eradication of male-fertile clones to prevent production of backcross seed.


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07/07/09 Original text by:

John Bailey, University of Leicester, UK

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