Reinstatement of Cyclocarya serrata (Juglandaceae) based on ploidy, morphology, niche and phylogenetics

<i>Pterocarya serrata</i> C.K.Schneid., originally described in 1912, has long been treated as a synonym of <i>Cyclocarya paliurus</i> (Batal.) Iljinsk. in Plants of the World Online (POWO). Based on an integrative framework combining ploidy determination, morphometric analyses, ecological niche comparisons, and molecular phylogenetics of mixed-ploidy populations, together with extensive herbarium and field investigations, we formally reinstate <i>Pterocarya serrata</i> as a distinct species within the genus <i>Cyclocarya</i>, recognizing three synonyms. Our results reveal clear phenotypic divergence and genetic differentiation between <i>C. serrata</i> and <i>C. paliurus</i>, which have evolved into separate evolutionary lineages. These findings refute the traditional treatment of <i>Cyclocarya</i> as a monotypic genus. Furthermore, we present the first comprehensive morphological descriptions, distribution records, and taxonomic notes for both <i>C. serrata</i> and <i>C. paliurus</i>, thereby advancing the systematic understanding of <i>Cyclocarya</i>.