The gall-making sawfly, Pontania (Eupontania) aestiva (Thomson, 1862) (= P. norvegica Kopelke, 1991, ?P. varia Kopelke, 1991) is treated as a valid species. The lectotype of Nematus aestivus Thomson, 1862 is redescribed. Pontania aestiva produces leaf-galls on Salix myrsinifolia (= nigricans, borealis) in Northern Europe and probably in the mountains of Central Europe. Populations of this species from the British Isles are considered as a separate subspecies, P. aestiva harrisoni Benson, 1940. Galls found on Salix purpurea x viminalis and S. purpurea in Northern England and Southern Scotland have an unusual shape, which probably is correlated with development on a subsidiary host plant. Similar host induced differences have been shown for P. viminalis (Linnaeus, 1758), which has normal galls on Salix purpurea, but abnormal galls on Salix babylonica reared under laboratory conditions. Morphological differences of adults are described to differentiate the sawfly species.