Genome skimming provides new insight into the relationships in Ludwigia section Macrocarpon (Onagraceae), a polyploid complex

Interpreting relationships within groups containing polyploids, which are frequent in angiosperms, can be greatly assisted by genomic techniques. In this study, we used a genome-skimming approach to investigate the evolutionary relationships and origins of polyploids in the monophyletic group, Ludwigia section Macrocarpon (Onagraceae), which includes diploid, tetraploid, and hexaploid taxa. Our results showed that the South American diploid taxa L. bonariensis and L. lagunae were closely related. We reported the first chromosome count (2n = 4x = 32) for L. neograndiflora, which is closely related to the two South American diploid taxa, although its exact origin remains unclear. The samples of the widespread, polyploid taxon L. octovalvis do not form a monophyletic group. Both tetraploid and hexaploid L. octovalvis lineages have originated more than once. At least one tetraploid L. octovalvis lineage may have been involved in the origins of hexaploids. One or more extinct/unsampled intermediate tetraploid L. octovalvis lineages were also likely involved the origins of hexaploids.