Complete name: Fallopia japonica (Houtt.) Ronse Decraene var. japonica; Fallopia sachalinensis (F. Schmidt) Ronse Decraene; Fallopia x bohemica (Chrtek & Chrtková) J. P. Bailey
Taxonomy: Magnoliophyta » Magnoliophyta » Rosopsida » Caryophyllales » Polygonaceae » Fallopia japonica
Authors: Petr Pysek
Last updated: September 21th, 2006

Japanese knotweed s.l.

Fallopia japonica (Houtt.) Ronse Decr.
Pleuropterus cuspidatus (S. et Z.) H. Gross
Polygonum cuspidatum Siebold & Zucc.
Polygonum reynoutria Makino
Polygonum sieboldii Reinw. ex de Vries
Polygonum zuccarinii Small
Reynoutria japonica Houtt.
Tiniaria cuspidata (Houtt.) Hedb.
Tiniaria japonica (Houtt.) Hedberg

Herbaceous perennials with robust erect stems up to 4 m tall and extensive system of rhizomes, 15-20 m long, penetrating 2-3 m deep in soil. The invasive knotweeds in Europe include Fallopia japonica var. japonica, F. sachalinensis, and their hybrid, F. x bohemica.

• Dispersal Mechanisms
  • Human-transported soil contaminated with rhizomes is the major dispersal mode. Rhizome fragments as small as 7 g fresh weight are able to regenerate, provided a node is present. The hybrid has better regeneration ability than both parents. Some clones of knotweeds can persist in localities for >130 years.
• Reproduction
  • Knotweeds are functionally dioecious. Flowers are exclusively entomophilous. Only one Fallopia japonica var. japonica female clone has been introduced and spread over Europe, earning the nickname "world's largest female". The number of flowers per stem exceeds 190,000; they can be fertilized by the pollen of F. sachalinensis, resulting in F. x bohemica, or by a congeneric climber F. aubertii, in which case only a low percentage are fertilized and seedling establishment is inefficient. When seed is produced, the winged achenes are dispersed by wind and water.
• Known Predators/Herbivores
  • Palatable to sheep, donkeys, goats, cattle, and horses. House sparrows have been observed removing F. japonica achenes. The extrafloral nectaries present at the base of the leaves attract predatory ants. Fallopia japonica is a host to several fungal species. Although herbivorous insects feeding on the foliage of both F. japonica and F. sachalinensi in Japan can consume >40% of the total leaf area, invertebrate predators do not cause damage in the invaded range.
• Resistant Stages (seeds, spores etc.)

• Native (EUNIS Code)
  • H6: Recent volcanic features.
• Habitat Occupied in Invaded Range (EUNIS Code)
  • E2: Mesic grasslands, E3: Seasonally wet and wet grasslands, F9: Riverine and fen scrubs, FA: Hedgerows, J6: Garrigue.
• Habitat Requirements
  • In its native range, F. japonica is a pioneer species on volcanic slopes. Fallopia sachalinensis occurs in tall-forb communities at forest edges, avalanche clearings, riverbanks and coastal cliffs, but also colonizes lava flows. Knotweeds invade disturbed habitats and thrive on a wide range of soils, with pH ranging from 3 to 8.

Fallopia japonica and F. sachalinensis were introduced into Europe as garden ornamentals in the 19th century and soon escaped from cultivation. Because of its showy blossoms, F. japonica became a popular plant in Victorian gardens of Europe, winning a gold medal in 1847 from the Society of Agriculture and Horticulture at Utrecht as the most “interesting” plant of the year. The hybrid was not reported from Japan until 1997; this indicates that it resulted from hybridization in the invaded range.

• Native Range
  • Knotweeds are native to East Asia, F. japonica to Japan, Korea, Taiwan, and northern China, F. sachalinensis from Sakhalin Island southwards through Hokkaido to Honshu.
• Known Introduced Range
  • Fallopia japonica is invasive in most European countries, Canada and USA, and reported from Australia and New Zealand. The distribution of F. sachalinensis in Europe is similar to that of F. japonica but it does not occur quite as far south. It is also reported from USA, Canada, New Zealand and naturalized in S Japan.
• Trend
  • All three taxa are increasing. The hybrid is competitive and is spreading at a faster rate in Central Europe.

known distribution area (in CGRS grid squares; in countries; along coast)

	eradicated
	extinct
	not present; eradicated
	native distribution range in CGRS grid squares
	native range
	assumed native range
	infrequent distribution
	key distribution area
	not established

• Ecosystem Impact
  • Fallopia japonica damages native riparian communities by reducing light availability, through the alteration of the soil environment and through the release of allelochemicals. Soil K and Mn is greater under F. japonica than under native vegetation. Fallopia japonica decreases soil bulk density and increases organic matter content, water content and nutrient levels. It affects other trophic levels: the biomass of green frog Rana clamitans was found to be negatively related to F. japonica cover.
• Health and Social Impact
  • Unknown.
• Economic Impact
  • Prolific rhizome and shoot growth can damage foundations, walls, pavements, and drainage works, and causes flood hazards by increasing resistance to water flow and damaging flood prevention structures. Knotweeds are an excellent food source for honeybees. Young shoots are consumed in its native range and North America. Secondary compounds isolated from F. japonica include the anti-cancer phytoalexin resveratrol.

• Prevention
  • Plant debris should not be released in the wild.
• Mechanical
  • The combination of digging the soil surface and spraying with glyphosate is the most efficient. Fallopia sachalinensis is the easiest to control of the three taxa, the hybrid is the most resistant.
• Chemical
• Biological
  • In the native range of Japan, the leaf-feeding chrysomelid beetle Gallerucida nigromaculata regulates F. japonica population growth, and is under consideration as a biocontrol agent in the United Kingdom and USA.

The following contributors have provided records in the DAISIE database for this species.

The following experts registered themselves as having knowledge about this species or its family.

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Barney JN, Tharayil N, DiTommaso A., Bhowmik PC (2006) The biology of invasive alien plants in Canada. 5. Polygonum cuspidatum Sieb. & Zucc. [= Fallopia japonica (Houtt.) Ronse Decr.]. Canadian Journal of Plant Sciences 86:887-905

Child L, Wade M (2000) The Japanese knotweed manual. Packard Publishing, Chichester, p 123

Adachi N, Terashima I, Takahashi M (1996) Central dieback of monoclonal stands of Reynoutria japonica in an early stage of primary succession on Mt. Fuji. Ann Bot (Lond.) 77:477-486

Adachi N, Terashima I.,Takahashi M (1996) Mechanism of central die-back of Reynoutria japonica in volcanic desert on Mt. Fuji. A stochastic model analysis of rhizome growth. Ann Bot (Lond.) 78:169-179

Adachi N, Terashima I, Takahashi M. (1996) Nitrogen translocation via rhizome systems in monoclonal stands of Reynoutria japonica in an oligotrophic desert of Mt. Fuji: Field experiments. Ecol Res 11:175-186

Bailey JP (1994) The reproductive biology and fertility of Fallopia japonica (Japanese Knotweed) and its hybrids in the British Isles. Pages 141-158 in L. de Waal, L. E. Child, M. Wade and J. H. Brock, editors. Ecology and management of invasive riparian plants. John Wiley and Sons, Chichester

Bailey JP (2001) Fallopia x conollyana The Railway-yard Knotweed. Watsonia 23:539-541

Bailey JP, Child LE, Conolly AP (1996) A survey of distribution of Fallopia x bohemica (Chrtek et Chrtková) J. Bailey (Polygonaceae) in the British Isles. Watsonia 21:187-198

Bailey JP, Child LE, Wade M (1995) Assessment of the genetics variation of British populations of Fallopia japonica and its hybrid Fallopia x bohemica. Pages 141-150 in P. Pysek, K. Prach, M. Rejmánek and M. Wade, editors. Plant invasions: general aspects and special problems. SPB Academic Publishing, Amsterdam

Bailey JP, Conolly AP (1985) Chromosome numbers of some alien Reynoutria species in the British Isles. Watsonia 15:270-271

Bailey JP, Conolly AP (2000) Prize-winners to pariahs: A history of Japanese Knotweed s. l. (Polygonaceae) in the British Isles. Watsonia 23:93-110

Bailey JP, Stace CA (1992) Chromosome number, morphology, pairing, and DNA values of species and hybrids in the genus Fallopia (Polygonaceae). Pl Syst Evol 180:29-52

Barney JN (2006) North American history of two invasive plant species: phytogeographic distribution, dispersal vectors, and multiple introductions. Biol Invas d.o.i. 10.1007/s10530-005-3174-9

Beerling DJ (1990) The use of non-persistent herbicides, glyphosate, and 2,4-D amine, to control riparian stands of Japanese knotweed (Reynoutria japonica Houtt.). Regul Rivers Res Manag 5:413-417

Beerling D J (1991) The testing of cellular concrete revetment blocks resistant to growths of Reynoutria japonica Houtt. (Japanese knotweed). Water Res Ox 25: 495-498

Beerling D J (1993) The impact of temperature on the northern distribution of the introduced species Fallopia japonica and Impatiens glandulifera in North-West Europe. J Biogeogr 20: 45-53

Beerling DJ, Bailey JP, Conolly AP (1994) Biological flora of the British Isles: Fallopia japonica (Houtt.) Ronse Decraene. J Ecol 82:959-980

Beerling DJ, Huntley B, Bailey JP (1995) Climate and the distribution of Fallopia japonica: use of an introduced species to test the predictive capacity of response surfaces. J Veg Sci 6:269-282

Beerling DJ, Palmer JP (1994) Status of Fallopia japonica (Japanese knotweed) in Wales. Pages 199-212 in L. C. De Waal, L. Child, M. Wade, and J. H. Brock, editors. Ecology and management of invasive riverside plants. John Wiley & Sons, Chichester

Bímová K, Mandák B., Pysek P (2001) Experimental control of Reynoutria congeners: a comparative study of a hybrid and its parents. Pages 283-290 in G. Brundu, J. H. Brock, I. Camarda, L. E. Child and M. Wade, editors. Plant invasions: Species ecology and ecosystem management. Backhuys Publishers, Leiden

Bímová K, Mandák B., Pysek P (2003) Experimental study of vegetative regeneration in four invasive Reynoutria taxa (Polygonaceae). Plant Ecol 166:1-11

Bram MR, McNair JN (2004) Seed germinability and its seasonal onset of Japanese knotweed (Polygonum cuspidatum). Weed Sci 52:759-767

Brock JH, Wade M (1992) Regeneration of Japanese knotweed (Fallopia japonica) from rhizomes and stems: observation from greenhouse trials. IX Colloque International Sur la Biologie des Mauvaise Herbes 9:85-93

Conolly AP (1977) The distribution and history on the British Isles of some alien species of Polygonum and Reynoutria. Watsonia 11:291-311

de Waal LC (2001) A viability study of Fallopia japonica stem tissue. Weed Research 41:447-460

Ferris C (1999) Chloroplast DNA variation and hybridisation between invasive populations of Japanese knotweed and giant knotweed (Fallopia, Polygonaceae). Bot J Linn Soc 129:139-154

Forman J, Kesseli RV (2003) Sexual reproduction in the invasive species Fallopia japonica (Polygonaceae). Amer. J. Bot. 90:586-592

Gover AE, Johnson JM, Kuhns LJ (2000) Comparison of rehabilitation sequences for Japanese and Sakhalin knotweed infestations. Proc. Northeast Weed Sci Soc 54:78-80

Gover AE, Johnson JM, Kuhns LJ (2005) Control of Japanese knotweed with foliar herbicide applications. Proc. Northeast Weed Sci Soc 59:25

Hart ML, Bailey JP, Hollingsworth PM, Watson KJ (1997) Sterile species and fertile hybrids of Japanese knotweeds along the river Kelvin. Glasg Nat 23:18-22

Hirose T (1984) Nitrogen use efficiency in growth of Polygonum cuspidatum Sieb. et Zucc. Ann Bot 54:695-704

Hirose T, Kitajima K (1986) Nitrogen uptake and plant growth I. Effect of nitrogen removal on growth of Polygonum cuspidatum. Ann Bot (Lond.) 58:479-486

Hirose T, Tateno M (1984) Soil nitrogen patterns induced by colonization of Polygonum cuspidatum on Mt. Fuji. Oecologia 61:218-223

Hollingsworth ML, Bailey JP (2000) Evidence for massive clonal growth in the invasive Fallopia japonica (Japanese Knotweed). Bot. J Linn Soc 133:463-472

Hollingsworth ML, Bailey JP (2000) Hybridisation and clonal diversity in some introduced Fallopia species (Polygonaceae). Watsonia 23:111-121

Hollingsworth ML, Hollingsworth PM, Jenkins GI and Bailey JP (1998) The use of molecular markers to study patterns of genotypic diversity in some invasive alien Fallopia ssp. (Polygonaceae). Molec Ecol 7:1681-1691

Horn P, Prach K (1995) Aerial biomass of Reynoutria japonica and its comparison with that of native native species. Preslia 66: 345-348

Kim JY, Park CW (2000) Morphological and chromosomal variation in Fallopia section Reynoutria (Polygonaceae) in Korea. Brittonia 52:34-48

Kimura Y, Okuda H (2001) Resveratrol isolated from Polygonum cuspidatum root prevents tumor growth and metastasis to lung and tumor-induced neo vascularization in Lewis lung carcinoma-bearing mice. J Nutr 131:1844-1849

Mandák B, Pysek P, Bímová K (2004) History of the invasion and distribution of Reynoutria taxa in the Czech Republic: a hybrid spreading faster than its parents. Preslia 76:15-64

Mandák B, Pysek P, Lysák M,. Suda J, Krahulcová A, Bímová K (2003) Variation in DNA-ploidy levels of Reynoutria taxa in the Czech Republic. Ann Bot 92:1-8

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Sukopp H, Starfinger U (1995) Reynoutria sachalinensis in Europe and in the Far East: a comparison of the species ecology in its native and adventive distribution range. Pages 151-159 in P. Pysek, K. Prach, M. Rejmánek and M. Wade, editors. Plant Invasions: General aspect and special problems. SPB Academic Publishing, Amsterdam

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