Euphorbia palustris L. (Euras.) – A very rare but lately much increasing, locally naturalized escape from or relic of cultivation. Already known in the first half of the 19th century in Belgium (e.g. Crépin 1860) and sometimes claimed as a native species. However, much decreasing in the past and probably no longer seen in the 20th century (a claim from Groot Schietveld in Brasschaat in 1991 requires confirmation). Recently introduced in newly created nature reserves, especially in West-Vlaanderen. First documented from Rhodesgoed in Kachtem (Roeselare) where it was introduced around 2004. It was initially found in small number on the exposed pond margins but soon started expanding. By now it is represented by many hundreds of individuals in a river valley and adjacent damp meadows (Verloove 2008). Similar behaviour has been recorded from several different other localities in West-Vlaanderen (e.g. Wevelgem, Kortemark, Zillebeke, Uitkerke, Avelgem, Kortrijk; see also here for an up-to-date overview: http://waarnemingen.be/soort/view/2504).
Euphorbia palustris grows in damp, rather nitrophilous habitats. The extant populations apparently represent a very competitive race (originating in cultivation?). In large parts of its native area Euphorbia palustris is, in turn, much decreasing and endangered in its native habitats (Wärner & al. 2011).
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Selected literature:
Crépin F. (1860) Manuel de la flore de Belgique. Bruxelles, Librairie Agricole d'Emile Tarlier.
Rehbein R. (1999) Bemerkenswerte Pflanzen und Pflanzengesellschaften aus dem Rostocker Raum III: Euphorbia palustris L. Botanischer Rundbrief für Mecklenburg-Vorpommern 33: 47-54.
Verloove F. (2008) Enkele nieuwe neofyten in België en Noordwest-Frankrijk. Dumortiera 94: 1-8. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_94/Dum%2094_1-8_Nieuwe%20neofyten_Verloove.pdf]
Wärner C., Welk E., Durka W., Wittig B. & Diekmann M. (2011) Biological flora of Central Europe: Euphorbia palustris L. Perspectives in Plant Ecology, Evolution and Systematics 13(1): 55-69. [available online at: http://www.ufz.de/export/data/1/22233_Waerner_etal_2011.pdf]