Revision of Ludwigia hexapetala from Tue, 2013-10-08 15:52

Ludwigia hexapetala (Hook. et Arnott) Zardini, Gu et Raven (syn.: L. grandiflora (Michaux) Greuter et Burdet subsp. hexapetala (Hook. et Arnott) Nesom et Kartesz) (S-Am. to southern N-Am.) – A rare but much increasing escape from cultivation or garden throw-out. Apparently first collected in Louvain-la-Neuve (ferme de Biéreau le long de la Scavée du Biéreau) in 1983 but obviously deliberately introduced there (Bauchau & al. 1984). However, the spectacular increase of records started in the 1990’s. Ludwigia hexapetala was first recorded on the verge of an artificial basin in Woumen in 1996 (close to the Blankaart nature reserve; Demarest 1996). In the same year also collected in Flavion (pond in an estate). See also Duvigneaud & al. (1996) for an overview.  Important populations were discovered in 1997 (Schulens Meer), 1999 (Ieper; Ronse & Vanhecke 2000), 2006 (Hautrage; extremely invasive in Lac Grand Rieu and Lac de Tertre), etc. Most records are from artificial ponds and other water bodies. However, since about 2001 also known from numerous localities alongside river Kleine Nete. Verloove (2002) provides a detailed overview of its presence and spread in Flanders at that time. The distribution map for Flanders, presented by Vanhecke (2006), shows that Ludwigia hexapetala is still rare but it is usually extremely abundant where-ever present. An up-to-date distribution map for Flanders is available here: The species seems less frequent in Wallonia although, at least locally, very large populations have been recorded.

Vulnerable native aquatic species are probably readily outcompeted. Especially in hotter summers Ludwigia hexapetala often proliferates in an extreme way. Water recreation and fishing soon become impossible. The production of huge amounts of biomass sometimes severely affects sewer works. Its proliferation further induces a silting up of aquatic ecosystems, slowing down of water circulation, a strong local reduction of aquatic fauna, fall of oxygen concentration,… (Dandelot & al. 2005). The species apparently easily survived the cold winters of the mid 1980’s (Bauchau & al. 1984) and, more recently, those of 2009-2013. Its populations probably suffer slightly from long and deep frost (and may reduce in size) but not sufficiently so to become extinct. Contrary to the following species, it rarely (if at all) produces fruits in western Europe (Dandelot & al. 2005; see, however, Armitage & al. 2013). Ludwigia hexapetala is still available in Belgian plant nurseries but purchase is discouraged (AlterIAS). Additional information on its invasive behaviour in western Europe is available here:

Zardini & al. (1991) have shown that Ludwigia uruguyaensis (Cambess.) Hara (syn.: L. grandiflora) in fact encloses two closely related species, a decaploid race (L. hexapetala) and a hexaploid race (L. grandiflora s.str.). Both are morphologically very similar (which led Nesom & Kartesz 2000 to combine them as subspecies under the latter species). However, Ludwigia hexapetala is the more vigorous species with larger flowers and leaves (characters apparently inversed in Clement 2000!). Although both are cultivated as ornamentals in Europe (at least according to Hoch 1997), only Ludwigia hexapetala seems to be a noxious aquatic weed (Wagner & al. 2007). Distinguishing features for both species are discussed in Zardini & al. (1991) and Nesom & Kartesz (2000). All Belgian (and European) collections seen doubtlessly belong with Ludwigia hexapetala (see also Armitage & al. 2013).

Selected literature: Bauchau & al. (1984), Zardini & al. (1991), Kleuver & Holverda (1995), Demarest (1996), Duvigneaud & al. (1996), Hoch (1997), Clement (2000), Clement (2001), Nesom & Kartesz (2000), Ronse & Vanhecke (2000), Salanon (2000), Verloove (2002), Suddaby (2003), Vauthey & al. (2003), Dandelot & al. (2005), Vanhecke (2006), Wagner & al. (2007), Alberternst (2008), Nehring & Kolthoff (2011), Armitage & al. (2013).

Alberternst B., Nawrath S., Hussner A. & Starfinger U. (2008) Auswirkungen invasiver Arten und Vorsorge. Natur und Landschaft 83(9-10): 412-417.

Armitage J.D., Könyves K., Bailey J.P., David J.C. & Culham A. (2013) A molecular, morphological and cytological investigation of the identity of non-native Ludwigia (Onagraceae) populations in Britain. New Journ. Bot. 3(2): 88-95.

Bauchau V., Lejeune A. & Bouharmont J. (1984) Maintien et expansion de Ludwigia uruguayensis (Camb.) Hara en Brabant. Dumortiera 28:8-9.

Clement E.J. (2001) Ludwigia grandiflora established at Barton-on-Sea (v.c. 11, S. Hants). BSBI News 87: 52-54.

Dandelot S., Verlaque R., Dutartre A. & Cazaubon A. (2005) Ecological, dynamic and taxonomic problems due to Ludwigia (Onagraceae) in France. Hydrobiologia 551: 1-6.

Demarest L. (1996) Een nieuwe groeiplaats van Ludwigia grandiflora (Michaux) Greuter et Burdet: een bedreiging voor de Blankaart? Dumortiera 63: 7.

Duvigneaud J., Saintenoy-Simon J. & Delmarche C. (1996) Un complément à apporter à la Nouvelle Flore de la Belgique et des Régions voisines: le traitement du genre Ludwigia. Adoxa 10: 9-10.

Hoch P.C. (1997) Ludwigia. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 347-348.

Kleuver J.J. & Holverda W.J. (1995) Ludwigia uruguayensis (Camb.) Hara (Onagraceae), verwilderd. Gorteria 21: 99-100.

Nehring S. & Kolthoff D. (2011) The invasive water primrose Ludwigia grandiflora (Michaux) Greuter & Burdet (Spermatophyta: Onagraceae) in Germany: first record and ecological risk assessment. Aquatic Invasions 6(1): 83-89. [available online at:]

Nesom G.L. & Kartesz J.T. (2000) Observations on the Ludwigia uruguayensis complex (Onagraceae) in the United States. Castanea 65(2): 123-125.

Ronse A. & Vanhecke L. (2000) Ludwigia grandiflora in de grachten van Ieper (België) en Bergues (Noord-Frankrijk). Dumortiera 76: 29-30.

Salanon R. (2000) Trois xénophytes envahissantes des cours d'eau, récemment observées dans les Alpes-Maritimes (France): Myriophyllum aquaticum (Velloso) Verdcourt, Ludwigia grandiflora (Michaux) Greuter et Murdet et Sagittaria latifolia Willd. Biocosme Mésogéen 16(3): 125-145.

Suddaby R. (2003) Ludwigia grandiflora - a view from across the Channel. BSBI News 93: 57-59.

Vanhecke L. (2006) Ludwigia grandiflora. 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: 557.

Vauthey M., Jeanmonod D. & Charlier P. (2003). La jussie - Ludwigia grandiflora (Michx.) Greuter & Burdet - une nouvelle espèce pour la Suisse et un nouvel envahisseur. Saussurea 33: 109-117.

Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.

Wagner W.L., Hoch P.C. & Raven P.H. (2007) Revised classification of the Onagraceae. Syst. Bot. Monogr. 83: 1-240.

Zardini E.M., Gu H. & Raven P.H. (1991) On the separation of two species within the Ludwigia uruguayensis complex (Onagraceae). Syst. Bot. 16: 242-244.

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