Combining natal range distributions and phylogeny to resolve biogeographic uncertainties in balloon vines (Cardiospermum, Sapindaceae)

Abstract

Aim: A key aspect of effective invasive plant management is a clear understanding of natal ranges. In the balloon vine genus, Cardiospermum, uncertain native biogeographic ranges are hampering ongoing biological control efforts against invasive taxa in southern Africa. With the objective of minimizing non-target impacts, which are a major concern for conservation, we combine phylogenetic analyses with known native range distributions of selected Cardiospermum species to resolve unknown natal ranges for globally widespread balloon vines which occur in southern Africa. Location: Argentina, Australia, Brazil, Fiji, Hawaii, Mayotte, Namibia, South Africa, Tanzania, Tahiti and Uganda. Methods: Phylogenetic relationships and dispersal histories of known invasive and native populations of Cardiospermum species (C. corindum, C. grandiflorum, C. halicacabum and C. pechuelii) were inferred from network and phylogeny reconstructions for two plastid genes (rpl32 and trnL-F) to closely investigate relationships within and among balloon vine species. The timing of putative transoceanic dispersal events was determined from a dated nDNA (internal transcribed spacer, ITS) phylogeny using a relaxed molecular clock and a previously identified root age for the group. Results: Both phylogenies (cpDNA and nDNA) and the haplotype network (cpDNA only) indicated no clear genetic structure for Cardiospermum halicacabum world-wide, that is incongruence between geography and evolutionary relatedness. Similarly, we found no global geographic structure in C. grandiflorum, with the exception of Hawaiian and Ugandan accessions which formed a distinct monophyletic clade. In contrast, deep divergence was identified for C. corindum between southern Africa and native South American populations, both within the haplotype network and phylogenetic trees (dated at 5.9-15.1 Ma). More surprising, however, was the observed close phylogenetic relationship between the true African balloon vine species, C. pechuelii and African C. corindum, with the former rendering C. corindum paraphyletic, supporting the native status of the latter in southern Africa. Main conclusions: We conclude that C. halicacabum is likely non-native in southern Africa, while both C. corindum and C. pechuelii are native to southern Africa. We confirm the invasive status of C. grandiflorum in southern Africa and Australia but suggest that its status (native or invasive) be reviewed in other regions outside South America. We recommend that already-identified biological control agents with potential non-target impacts on C. corindum and C. pechuelii not be released against invasive Cardiospermum taxa in southern Africa and careful monitoring of such impacts for agents that have already been released prior to this study.