We analysed samples of Sparganophilus taken at the corners of its distribution area in Europe (UK, Germany and Italy). No mitochondrial genetic divergence within and amongst them was found, neither in COI nor in 16S. Further, the COI haplotype was also identical to two sequences from Ontario, Canada in the Barcoding of Life Data System (BOLD) database. Our European COI and 16S sequences showed only minimal differentiation (only 1 or 2 substitutions) from specimens newly collected in Illinois and Washington states (USA), as well as from a COI haplotype from Tennessee (USA) in BOLD. An additional COI haplotype from Illinois (found in BOLD) is 2.1% different from the other haplotypes but clearly belongs to the same lineage of Sparganophilus. This geographically broad but genetically compact group fits the morphological diagnosis of S. tamesis Benham, 1892 as revised by Jamieson (1971) and is seen as evidence that all European populations 1) belong to the same species, 2) derive from a recent introduction, 3) are conspecific with the most widespread species of Sparganophilus in North America, and that 4) S. tamesis is a senior synonym of S. eiseni Smith, 1895. The single European haplotype does not refute the possibility of its spread from a single introduced source population.