Introduction, Establishment and Replacement of Sea-Rockets (Cakile, Cruciferae) in Australia

Cakile edentula (Bigel.) Hook., native to sandy beaches of eastern North America, was first collected in Australia in the 1860s near Melbourne; it presumably was introduced in ships' ballast. Within 60 years it had spread along the coast of Victoria and to New South Wales, South Australia, Tasmania, and into southern Queensland, becoming locally abundant. C. maritima Scop., native to coastal beaches of the Mediterranean and Western Europe, was first collected in Australia in the 1890s near Perth; presumably it also was introduced in ships' ballast. It spread along the coast of southern Australia, and over the period 1920-60 replaced C. edentula in South Australia and Victoria. It has spread to New South Wales where it is now sympatric with C. edentula, while that species has recently extended its range the opposite direction, into Western Australia. The two beach species also co-occur in Tasmania. Areas of sympatry present opportunities for experimental and observational study of the likely competitive replacement of colonizing species.