Smilax sinovietnamensis, a New Quadrangular Stem Species of Smilacaceae Identified Through Integrative Taxonomy

A new species, Smilax sinovietnamensis P. Li & X.J. Jin, sp. nov. (Smilacaceae), from the Sino-Vietnamese Border, is described and illustrated. Using nuclear ribosomal DNA (nrDNA), chloroplast DNA (cpDNA), and orthologous nuclear genes (ONGs), we examined the phylogenetic position of this species within the family Smilacaceae. Furthermore, phylogenetic analyses of concatenated sequences of nrITS, five cpDNA (ndhA, ndhF, rpl16, matK, and rbcL), and two ONGs (At103 and Agt1) from 37 Smilacaceae species all strongly supported that S. sinovietnamensis is sister to S. cocculoides. Further comparative morphological analysis showed that S. sinovietnamensis can be clearly distinguished morphologically from its closely related species S. cocculoides. It has quadrangular stems and an abscission zone at one-third of the petioles’ length. Combining detailed morphological comparisons and molecular evidence, we confirm the novelty of S. sinovietnamensis. Additionally, we report the plastome characteristics of S. sinovietnamensis, enriching our understanding of the evolutionary relationships within Smilacaceae. Collectively, integrating diagnostic morphological traits with nrITS, cpDNA, ONGs, and the newly assembled plastome not only confirms S. sinovietnamensis as a new species but also offers practical tools for resolving taxonomic challenges in Smilacaceae. Additionally, the species’ unique quadrangular stem—an evolutionary morphology—provides significant reference value for understanding angiosperm evolution.