J Syst Evol

• Research Article •     Next Articles

Phylogenomics Reveal Incomplete Lineage Sorting as the Primary Source of Phylogenetic Discordance in East African Zanthoxylum and Vepris (Rutaceae)

Elizabeth Syowai Mutinda1,2,3, Wyclif Ochieng Odago1,2,3, Elijah Mbandi Mkala1,2,3, Emmanuel Nyongesa Waswa1,2,3, Jacinta Katunge Kawenze1,2,3, Moses Kirega Gichua4, Cai-Fei Zhang1,2,3, Guang‑Wan Hu1,2,3,5,6*, and Qing‑Feng Wang1,2,3   

  1. 1State Key Laboratory of Plant Diversity and Specialty Crops, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China
    2Sino-Africa Joint Research Center, Chinese Academy of Sciences, Wuhan 430074, China
    3University of Chinese Academy of Sciences, Beijing 100049, China
    4Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000-00200 Nairobi, Kenya
    5Hubei Jiangxia Laboratory, Wuhan 430200, China
    6State Key Laboratory for Quality Ensurance and Sustainable Use of Dao-di Herbs, Beijing, 100700, China
    *Author for correspondence. E-mail: guangwanhu@wbgcas.cn
  • Received:2026-04-06 Accepted:2026-06-24
  • Supported by:
    This work was supported by grants from the Key Project at Central Government Level: The Ability Establishment of Sustainable Use for Valuable Chinese Medicine Resources (2060302), the National Natural Science Foundation of China (32270228), the Science and Technology Major Project of Xizang (XZ202501ZY0151.4), the Project for Scientists in Biological Taxonomy of the Chinese Academy of Sciences (CAS-TAX-24-39), the Key R&D Program of Hubei Jiangxia Laboratory (JXBS010) and the Sino-Africa Joint Research Center, CAS, (SAJC202401).

Abstract: Evolutionary relationships of Zanthoxylum L. and Vepris Comm. ex A Juss. remain inadequately resolved due to limited genomic resources and conflicting signals from single markers, hindering efforts to understand their diversification and adaptation across tropical environments. In this study, we generated Angiosperms353 target-capture data for 187 individuals representing 51 Zanthoxylum and Vepris species from East Africa. Using concatenated and multispecies coalescent analyses combined with concordance-factor approaches, we recovered Zanthoxylum and Vepris as monophyletic. However, species-level relationships within each genus exhibited substantial phylogenetic discordance, indicating extensive gene-tree heterogeneity across the dataset. Concordance factor analysis revealed moderate genome-wide site concordance (mean sCF=46.64%) but markedly lower gene concordance (mean gCF=28.77%), indicating widespread gene-tree heterogeneity. Both sCF and gCF exhibited strong positive correlations with branch lengths of r=0.698 and r=0.687, respectively. Discordance patterns showed an almost perfect balance between alternative topologies (sDF1=24.9%, sDF2=24.8%), minimal mean asymmetry (3.5-5.1%), and high proportion of polyphyly (gDFP=59.7%), all consistent with incomplete lineage sorting (ILS) as the primary source of phylogenomic conflict. A small fraction of branches (1.9–4.7%) displayed significant asymmetry, which signals only limited evidence for processes beyond ILS and should be interpreted with caution pending explicit tests of introgression. Generally, our findings offer a comprehensive phylogenomic framework for East African Zanthoxylum and Vepris and demonstrate that ILS has played a major role in shaping genomic variation and phylogenetic discordance within these genera. Further analyses will be required to investigate the extent to which hybridization or other reticulate processes have contributed to their evolutionary history.