4. Bidens radiata Thuill. (Eur., C-As.) – An exceptional alien, discovered in small number in 2005 in an exposed fish pond near Zonhoven but not confirmed afterwards. Discovered in abundance on the muddy margins of temporary ponds in the port of Zeebrugge (sand raised sites) and near a sugar refinery in Waremme in 2008. At least in the former locality persisting very well and still present in 2011 (along with other alien Asteraceae like Artemisia biennis and Cotula coronopifolia).
Bidens radiata is a poorly known species in Belgium. It has been claimed on various occasions but all records, except the above, proved to be in error for native Bidens tripartita. In addition to the characters mentioned in the key Bidens radiata is usually yellowish-greenish, leaf serrations are curved inwards (straight or curved outwards in B. tripartita) and achenes are considerably smaller and much narrowed towards base.
Residence status of Bidens radiata in Belgium is controversial. There are surely no historical records. The recent ones suggest an introduction by migrating birds (see also Duvigneaud 1975a).
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Selected literature:
Duvigneaud J. (1975a) Présence de Bidens radiata Thuill. dans le département du Nord (France). Nat. Mosana 28(1): 14-15.
Diekjobst H. (1981) Atriplex hastata- und Bidens radiata-Gesellschaft im therophytischen Vegetationskomplex am Möhnesee. Natur und Heimat 41: 3-12.
Hoffer-Massard F. (2012) Polypogon viridis (Gouan) Breitsr. : encore une nouveauté en Suisse romande. Bulletin du Cercle vaudois de botanique 41: 99-100. [available online at: http://doc.rero.ch/record/203205?ln=fr]
Jansen M.T. (1993) Bidens radiata Thuill. langs de Waal in 1989, 1990 en 1991. Gorteria 18(5-6): 117-121.