Open Access

Roger D. Cousens, Peter K. Ades, Mohsen B. Mesgaran, Sara Ohadi

• In this paper we revisit the invasion history of two species of Cakile in Australia. Cakile edentula subsp. edentula arrived in the mid 19th Century and spread into coastal strandline habitat from the southeast towards the west and to the north; Cakile maritima arrived in the late 19th Century and has replaced Cakile edentula over much of the range. While Cakile edentula is morphologically quite uniform, the great variation within Cakile maritima has confused field ecologists. Using herbarium records we update previous accounts of the spread of the species and report on field surveys that determined their current geographic overlap in Tasmania and in northern New South Wales/southern Queensland. We examine regional morphological variation within Cakile maritima using the national herbaria collections and variation within new population samples. We support previous interpretations that Cakile maritima has been introduced on more than one occasion from morphologically distinct races, resulting in regional variation within Australia and high variability within populations in the south-east. Western Australian populations appear distinct and probably did not initiate those in the east; we consider that eastern populations are likely to be a mix of Cakile maritima subsp. maritima from the Mediterranean and Cakile maritima subsp. integrifolia from Atlantic Europe. Although introgression from Cakile edentula into Cakile maritima cannot be discounted from our results, it is not required to explain the levels of variation in the latter species observed in Australia. Cakile maritima continues to spread southwards in Tasmania and northwards in NSW; in Queenland, a recent occurrence has proliferated in Moreton Bay, spreading slowly to the north but not appreciably southwards.