Genetic variation of the invasive Campuloclinium macrocephalum, Asteraceae in South Africa, inferred from molecular markers.
Campuloclinium macrocephalum is native to Central and South America, but is a highly invasive weed in South Africa, where it is commonly known as the 'pompom weed'. It is targeted for biological control, the success of which will depend on host specificity and biotype compatibility to its full genetic diversity in South Africa. We investigated the genetic diversity and phylogeography of 52 specimens from across South Africa, 14 from Argentina and three from Brazil using nuclear ribosomal ITS regions. We further explored the AFLP marker diversity in 54 South African, 25 Argentine and three Brazilian specimens. Maximum parsimony analysis of the ITS sequence data produced an unresolved phylogeny. However, three haplotypes were recognised via network analysis. All South African, one Brazilian and all bar one of the Argentine individuals shared a single haplotype. AFLP analyses generated two genetic clusters with a low net nucleotide distance of 0.115 and further revealed that most plants were a mixture of alleles from these two genetic clusters. Although there was a significant genetic variation among the populations, genetic differentiation and mean heterozygosity were low, suggesting that clonal reproduction may be occurring. The current South African populations may therefore be clonal products with different proportions of genetic admixture introduced more than once. The original point of entry appears to be Gauteng, South Africa. Long-distance dispersal appears to have played a major role in its spread across South Africa. Candidate Argentine biological control agents should therefore be effective on C. macrocephalum in South Africa.