A new section, Euphorbia sect. Bokorenses under subgenus Euphorbia is established for Euphorbia bokorensis H. Toyama & Tagane, sp. nov., endemic to Bokor National Park, Cambodia. Euphorbia sect. Bokorenses is distinguished from related sections Denisophorbia and Goniostema by unbranched stems and smooth seeds, respectively. Bayesian phylogeny using matK, ndhF, and ITS regions supports its monophyly from the currently recognized 21 sections. It has a sister relationship with the Malagasy clade, including sections Denisophorbia, Deuterocalli and Goniostema, and to the northeastern African clade, including sect. Rubellae. A description, illustration, photographs and preliminary conservation status of the new species, and an updated identification key to the sections of Euphoria subg. Euphorbia is provided.
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