| The tribe Millettieae, which consists of about 50 genera and 1000 species, is generally thought to be the intermediate group between several other tribes in Papilionoideae. Traditionally, Millettieae comprise taxa transferred from Dalbergieae (Lonchocarpus, Derris, and allies), and taxa transferred from Galegeae (Millettia, Tephrosia , and allies). These taxa form a "chained-taxa" in legumes, and the phylogeny of these taxa and other Papilionoideae taxa has not been resolved based on morphological studies.; In this study, the phylogeny of Millettieae and related taxa was reconstructed by using DNA sequences of the chloroplast trnK/mat K and nuclear ribosomal ITS regions. The results show that the traditional Millettieae taxa can be divided into three different groups. First is the core Millettieae group, which consists of the four largest genera in this tribe, Tephrosia, Millettia, Lonchocarpus , and Derris. Second is the Callerya group, comprising Callerya, Wisteria, and Afgekia, which is within a well-supported clade, denoted IRLC (Inverted Repeat Lacking Clade), along with all the other legumes that lack one copy of the inverted repeat in the chloroplast genome. The third group contains two taxa, Cyclolobium and Poecilanthe, which form a clade containing Brongniartieae, and are distantly related to other Millettieae. The results indicate that the genera Lonchocarpus and Derris are not closely related to Dalbergieae as suggested by other studies, and the similar pod morphology between these taxa must be due to homoplasy. The core Millettieae group overlaps with Phaseoleae on the trees obtained in this study. The combined core Millettieae-Phaseoleae clade shows several trends: the inflorescences are mostly pseudoracemes or pseudopanicles, and alternative non-protein amino acids are used instead of canavanine. The core Millettieae-Phaseoleae clade also contains tribes Psoraleeae, Desmodieae, and Abreae based on the molecular phylogeny.; Codon usage and amino acid composition of the chloroplast trn K/matK region from legumes and selected seed plants was studied in detail, The results show that codon usage is influenced by nucleotide composition (G+C content). It also demonstrates the potential utility of codon usage information in phylogenetic study. |
