Abstract Flow cytometry estimation of 2C nuclear DNA content of the examined Nasturtium species resulted in taxonomic identification of N. × sterile in eight new localities, N. microphyllum in four new localities and N. officinale in one new locality in western Poland. Scanning electron microscopy proved a few of the micromorphological traits of seeds and fruits (size and shape of cells on the fruit septum surface, their anticlinal walls; secondary sculpture on the outer periclinal walls of cells on the siliqua valve internal surface) to be of taxonomic importance.