Cabombaceae
Cabombaceae is closely related with Nymphaeaceae and often united with it. However, recent molecular phylogenetic research defends its segregation (Taylor 2008, APGIII 2009).
A single genus, Cabomba, has been recorded in the wild in Belgium.
Literature:
APG III (2009) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants. APG III. Bot. J. Linn. Soc. 161(2): 105-121.
Taylor D.W. (2008) Phylogenetic Analysis of Cabombaceae and Nymphaeaceae Based on Vegetative and Leaf Architectural Characters. Taxon 57(4): 1082-1095.