Phylogenomics reveals a new generic delimitation of Asian Millettia, with reinstatements of Pongamia and Otosema (Fabaceae: Millettieae).

Mol Phylogenet Evol

Key Laboratory of National Forestry and Grassland Administration on Plant Conservation and Utilization in Southern China, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, PR China; South China National Botanical Garden, Guangzhou 510650, PR China. Electronic address:

Published: November 2024

AI Article Synopsis

  • The classification of the Millettieae group, particularly the Millettia genus with around 150 species, has been challenging and is shown to be polyphyletic based on new molecular evidence.
  • This study utilized genome sequencing to clarify relationships within Millettieae, revealing three distinct subclades in Asian Millettia and proposing a narrower definition of the genus, while also reinstating two other genera, Pongamia and Otosema.
  • Findings highlighted that African Millettia species are distinctly different from Asian ones and that the rapid diversification of these plants during the Mid-Miocene Climatic Optimum may contribute to their complex classification issues.

Article Abstract

The generic relationships within the core Millettieae have not been well resolved to date. Millettia is considered one of the most problematic genera to classify within the core Millettieae, with approximately 150 species found in Asia and Africa. Recent molecular evidence has indicated that Millettia is highly polyphyletic. In this study, we utilized plastomes and single-copy nuclear genes from genome skimming sequencing to reconstruct the generic relationships and estimate the divergence time for the core Millettieae, focusing on the Asian species of Millettia. Our results revealed a broader circumscription of the core Millettieae with the inclusion of the Phaseoleae subtribe Ophrestiinae, consisting of 7 clades and 14 subclades within two main groups (canavanine and non-canavanine). The Asian species of Millettia were grouped into three distinct, well-supported subclades, leading us to propose a much narrower generic concept of Millettia, along with the reinstatements of the genera Pongamia and Otosema. Millettia s.str. was restricted to include only seven species. Pongamia was recognized as a medium-sized genus that includes Fordia and Ibatiria, with approximately 56 species. Otosema, usually treated as a subgenus or section of Millettia, was resurrected as a distinct genus with three species. Our findings also indicated that the sampled African Millettia species belong to three subclades distinct from the Asian Millettia subclades, warranting further investigation in future studies. The dating result showed that the early rapid diversification of the core Millettieae during the Mid-Miocene Climatic Optimum involved several major problematic genera, including Derris s.lato, Lonchocarpus s.lato, and Millettia s.lato, which may explain why these plant groups are difficult to classify. These results offer new insights into the phylogeny and taxonomy of the core Millettieae.

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http://dx.doi.org/10.1016/j.ympev.2024.108254DOI Listing

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