Abstract
Gomphocarpus fruticosus L. W.T. Aiton (narrow leaf cotton bush), native to southern and eastern Africa and the Arabian Peninsula, is invasive in southern and eastern Australia, and has been considered as a target for classical biocontrol. To improve our understanding of the taxonomic identity and introduction history of Australian populations, and to assess their genetic diversity and structure, we analysed single nucleotide polymorphisms of plants from across Australia and a subset of the native range, generated using reduced-representation sequencing. We detected geographic structuring of genetic diversity within Australia, inferred to be the result of multiple introductions or evolutionary processes occurring post-introduction, as well as isolation by distance. Plants from Brisbane, Queensland, were found to share ancestry with G. fruticosus plants from Witswatersrand and a specimen identified as G. physocarpus from the Lydenburg District of South Africa, either reflecting the source population of introduction or descent from the same cultivar. Populations elsewhere in Australia were not closely related to any sampled population in the native range. We noted incongruence between subspecific determination of expert identified herbarium specimens and genetic clustering. These results have implications for any future biocontrol program for G. fruticosus in Australia. Prospective biocontrol agents would need to be tested on all genetically distinct clusters within Australia. Further research to determine subspecies identity and introduction history of Australia populations would need to focus on additional sampling in the native range, including all five recognised subspecies as well as any cultivars.