3. Reynoutria japonica Houtt. (syn.: Fallopia japonica (Houtt.) Ronse Decraene, Polygonum cuspidatum Siebold et Zucc.) (E-As.) – A widely naturalised and much increasing, invasive alien. Known in the wild in Belgium since at least 1882 (Vanden Berghen 1997) and by now one of the most undesirable non-native vascular plants in Belgium. Reynoutria japonica is found in a wide range of habitats: road verges, canal- and riverbanks, along railway tracks, wood margins, wasteland, former dumps,…. Additional information on the invasive behaviour of Reynoutria japonica in Belgium and elsewhere in western Europe is available at: http://ias.biodiversity.be/species/show/9 and http://www.q-bank.eu/Plants/Factsheets/Fallopia%20japonica%20NL.pdf.
An intergeneric hybrid of female Reynoutria japonica and male Fallopia baldschuanica (xReyllopia conollyana (J.P. Bailey) Galasso; syn.: Fallopia xconollyana J.P. Bailey) (see Bailey & Conolly 1984, Bailey 1988, Bailey 2001, Bailey & Spencer 2003, Galasso & al. 2009) was found as open pollinated seed from Reynoutria japonica on a canal bank between Merendree and Lovendegem in 2008. Offspring that was subsequently cultivated by Ivan Hoste produced plants that were perfectly intermediate between both parents. Spontaneously germinated plants of this hybrid have not been recorded so far in Belgium and appear to be very rare (see also Bailey 2001, Galasso & al. 2009).
Reynoutria japonica is one of the worst invasive species in Europe and there is a vast literature dealing with its invasiveness, ecology, biology, control and reproduction. Many additional references are provided in the references cited above. An overview for Europe with extensive bibliography is available at: http://www.europe-aliens.org/pdf/Fallopia_japonica.pdf.
There is evidence that climate warming enhances the sexual reproduction of Reynoutria japonica at its northern distribution limit (Groeneveld & al. 2014).
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Selected literature:
Bailey J.P. (1988) Putative Reynoutria japonica Houtt. x Fallopia baldschuanica (Regel) Holub hybrids discovered in Britain. Watsonia 17(2): 163-164.
Bailey J.P. (2001) Fallopia x conollyana. The Railway-yard Knotweed. Watsonia 23(4): 539-541.
Bailey J.P. & Conolly A.P. (1984) A putative Reynoutria x Fallopia hybrid from Wales. Watsonia 15: 162-163.
Bailey J.P. & Conolly A.P. (2000) Prize-winners to pariahs. A history of japanese knotweed s.l. (Polygonaceae) in the British Isles. Watsonia 23(1): 93-110.
Bailey J.P. & Spencer M. (2003) New records of Fallopia x conollyana: is it truly such a rarity? Watsonia 24(3): 452-453.
Beerling D.J., Bailey J.P. & Conolly A.P. (1994) Biological flora of the British Isles N° 183: Fallopia japonica. Journal of Ecology 82: 959-979.
Bzdęga K., Janiak A., Tarłowska S., Kurowska M., Tokarska-Guzika B. & Szarejko I. (2012) Unexpected genetic diversity of Fallopia japonica from Central Europe revealed after AFLP analysis. Flora 207: 636-645.
Christenhusz M.J.M. & van Uffelen G.A. (2001) Verwilderde Japanse planten in Nederland, ingevoerd door von Siebold. Gorteria 27: 97-108.
Conolly A.P. (1977) The distribution and history in the British Isles of some alien species of Polygonum and Reynoutria. Watsonia 11: 291-311.
Galasso G., Banfi E., De Mattia F., Grassi F., Sgorbati S. & Labra M. (2009) Molecular phylogeny of Polygonum L. s.l. (Polygonoideae, Polygonaceae), focusing on European taxa: preliminary results and systematic considerations based on rbcL plastidial sequence data. Atti Soc. It. Sci. Nat. Museo Civ. Stor. Nat. Milano 150(1): 113-148.
Groeneveld E., Belzile F. & Lavoie C. (2014) Sexual reproduction of Japanese knotweed (Fallopia japonica s.l.) at its northern distribution limit: new evidence of the effect of climate warming on an invasive species. Am. J. Bot. 101(3): 459-466.
Lambinon J. (1995) Notes taxonomiques, nomenclaturales et chorologiques relatives à la quatrième édition de la « Nouvelle Flore » de la Belgique et des régions voisines. 3. Données nouvelles sur des plantes adventices ou subspontanées en Belgique. Dumortiera 60: 1-36.
Pfeiffenschneider M., Gräser P. & Ries C. (2014) Distribution of selected neophytes along the national railway network of Luxembourg. Bulletin de la Société des naturalistes Luxembourgeois 115: 95-100. [available online at: http://www.snl.lu/publications/bulletin /SNL_2014_115_095_100.pdf]
Pfeiffenschneider M., Gräser P. & Ries C. (2014) Distribution of selected neophytes along the main rivers of Luxembourg. Bulletin de la Société des naturalists Luxembourgeois 115: 101-108. [available online at: http://www.snl.lu/publications/bulletin/SNL_2014_115_101_108.pdf]
Vanden Berghen C. (1997) La Renouée du Japon en Belgique. Adoxa 15-16: 35-38.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Verloove F. (2006) Fallopia japonica. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 400-401.