On the west coast of North America and in Australia, there have been parallel cases of sequential invasion and replacement of the shoreline plant American sea-rocket by European sea-rocket. A similar pattern has also occurred in New Zealand. For 30 to 40 yr, from its first recording in 1921, American sea-rocket spread throughout the eastern coastlines of the North and South Islands of New Zealand. European sea-rocket has so far been collected only on the North Island. From its first collection in 1937, European sea-rocket spread to the northern extremity of the island by 1973, and by 2010, it had reached the southernmost limit. In the region where both species have occurred in the past, American sea-rocket is now rarely found. This appears to be another example of congeneric species displacement.
