Morphological plasticity and species limits in <i>Smilax</i> sect. <i>Macranthae</i>: evidence for conspecificity of <i>S. wightii</i> and <i>S. zeylanica</i>

The genus <i>Smilax</i> exemplifies such complexity, particularly within the <i>S. ovalifolia–S. wightii–S. zeylanica</i> complex, which has long been subject to taxonomic uncertainties. Within this complex, <i>S. ovalifolia</i> represents a key reference lineage, exhibiting comparatively stable morphological and anatomical traits that contrast with the pronounced variability observed in <i>S. wightii</i> and <i>S. zeylanica</i>.

Building on this contrast, we integrate restriction-site associated DNA sequencing (RAD-seq) with detailed morphological, anatomical, and phylogenetic analyses to reassess species limits and lineage relationships. Genome-wide data provide a framework for evaluating evolutionary cohesion and reveal patterns of divergence not evident from morphology alone. Evidence from molecular phylogenetic analyses, neighbour-joining networks, and population genetic structure consistently supports the genetic distinctiveness of <i>S. ovalifolia</i>, while demonstrating a lack of meaningful genetic separation between <i>S. wightii</i> and <i>S. zeylanica</i>.