Could anyone please identify this flower/plant found on the semi-shaded banks of a river in East Ireland? It was located near Japanese Knotweed and looks quite similar to this.
Tall, stems often reddish. Lvs opposite or in threes, with small red teeth. Fls large, pale to dark pink-purple, with short bent spur; July-Oct. Bare places, especially by streams.
The Wild Flowers of Britain and Northern Europe. Fitter, Fitter, Blamey. 1974. Collins, London.