Multi-locus phylogeny of Ludwigia (Onagraceae): insights on infra-generic relationships and the current classification of the genus.
Ludwigia (Onagraceae) is a worldwide wetland genus with 83 species currently classified as members of 23 sections. Past studies have documented the morphological diversity and complex evolutionary history. Here we provide the first comprehensive molecular phylogeny of Ludwigia, using our new data to examine the existing evolutionary hypotheses. We employed both nuclear (ITS, waxy) and chloroplast (rps16, rpl16, trnL-trnF, trnL-CD, trnG) DNA regions for this study. Our results suggest that the North Temperate haplostemonous (NTH) group and a second group that includes all other species of Ludwigia (clade B) form strongly supported sister clades. In the NTH group, a monophyletic sect. Ludwigia is sister to the Microcarpium complex, but sect. Microcarpium and sect. Isnardia are not monophyletic. In clade B, the multi-species sections Jussiaea and Macrocarpon are well-supported monophyletic clades, but others, including the largest sect. Myrtocarpus, are not monophyletic. In sum, this first molecular phylogeny of Ludwigia clarifies and supports several major relationships in the genus but also highlights parts of the classification that should be changed. Our results imply that allopolyploidy played an important role in the evolutionary history of the genus, giving rise to complex patterns of relationships that are not yet adequately reflected in the classification.