Phylogenetic Analysis of the Lythraceae Based on Four Gene Regions and Morphology

Abstract

The family limits of the Lythraceae and relationships among the ca. 31 genera remain poorly known in spite of previous phylogenetic studies. We use morphology and DNA sequences from the rbcL gene, the trnL‐F region, and psaA‐ycf3 intergenic spacer of the chloroplast and the internal transcribed spacer region of the nucleus to explore relationships for up to 27 genera of the Lythraceae sensu stricto and the monogeneric families Duabangaceae, Punicaceae, Sonneratiaceae, and Trapaceae. Maximum parsimony, maximum likelihood, and Bayesian likelihood approaches are employed. Morphology alone provided little phylogenetic resolution. Results from individual gene regions were relatively well resolved and largely congruent, whereas basal relationships were poorly supported. A combined gene analysis of 20 genera produced one fully resolved maximum parsimony tree that corresponded closely to the maximum likelihood and Bayesian trees in which a monophyletic Lythraceae includes Duabanga, Punica, Sonneratia, and Trapa as derived genera within the family. Decodon is sister to the rest of the family in the maximum parsimony and Bayesian trees, followed by Lythrum and Peplis at the node above and then by the rest of the family, which diverges into two superclades. In the maximum likelihood tree, the family diverges at the base into two superclades. Six crown clades are well supported but lack unique morphological synapomorphies. Neither superclades nor crown clades correspond to the present tribal and subtribal classification. The New World genera are embedded in four Old World clades. If the basal and near‐basal positions for the Northern Hemisphere genera Decodon, Lythrum, and Peplis are confirmed, the origin of the family is more likely Laurasian than Gondwanan. The biogeography and early fossil record of the family indicate that the family originated by the late Cretaceous and had extensively diversified and radiated into Southeast Asia and North America by the lower Eocene.