A known naturalized population of Saururus in (Flanders) Belgium was included in
a molecular study and unexpectedly turned out to be of hybrid origin. This prompted
a targeted survey of all known naturalized populations of Saururus in the Netherlands
and Belgium. Plant material was analysed using both morphological and molecular
methods, and results were compared with herbarium specimens from the native
range and with DNA sequences available in GenBank. All naturalized populations
proved to be hybrids between Saururus cernuus and S. chinensis, the only two
species in the genus. A morphological key is provided to distinguish both parental
species and the hybrid.