Carpinus wenshanensis Xiaolong Zhou, a newly discovered hornbeam species endemic to Wenshan Prefecture in southeast Yunnan, China, is described and illustrated. This study employs an integrative taxonomic approach, combining morphological comparison, biogeographic distribution analysis, and phylogenetic reconstruction based on nuclear ITS sequences, to establish C. wenshanensis as a distinct species sister to C. tschonoskii. Carpinus wenshanensis is diagnostically characterized by six key morphological traits: (1) mucronate-serrate leaf margins (versus setiform serrate in C. tschonoskii); (2) serration restricted to the basal half of outer bract margins (versus extending across both basal and apical halves); (3) reduced serration number on outer bract margins (1–3 serrations per margin compared to 4–7); (4) nearly glabrous petioles and annual branchlets (versus sparsely or densely pubescent); (5) longer petioles (1.0–1.7 cm versus 0.6–1.3 cm); and (6) a variable leaf base shape (rounded, subrounded, cordate, or subcordate versus rounded-cuneate or cuneate). Additionally, population-level ITS sequence comparison identified three fixed nucleotide polymorphisms that unequivocally differentiate C. wenshanensis from its closest relative. Collectively, these findings provide robust evidence for recognizing C. wenshanensis as a novel species within the genus Carpinus.
