The material referred to Rorippa islandica (Oeder ex Murray) Borbas in the Flora van Nederland by HEUKELS-VAN OOSTSTROOM (1975), in fact represents Rorippa palustris (L.) Besser and turned out to be tetraploïd (2n = 32) in four Dutch populations. A comparison is made between R. palustris from the Netherlands and R. islandica from the Swiss Alps.