Morpho-anatomical variation and secondary metabolism associated with floral polymorphism in Cosmos sulphureus Cav

Cosmos sulphureus is widely recognized for its medicinal value, yet the relationship between its floral polymorphism and internal structural and phytochemical variation remains insufficiently understood. In this study, five natural varieties of C. sulphureus collected from southern Vietnam were examined using an integrated approach combining morphology, anatomy, and phytochemical analysis. Comparative assessments of vegetative and reproductive traits, stem and leaf anatomy, and lignin distribution revealed substantial variation,primarily associated with floral form. Multivariate analysis separated the varieties into three groups, largely distinguishing single-flowered from semi-double forms. Single-flowered varieties exhibited greater plant height and structural reinforcement, characterized by enlarged vascular tissues and continuous sclerenchyma in the stem. In contrast, semi-double varieties showed reduced lignification but markedly higher accumulation of secondary metabolites, including phenolics, flavonoids, and alkaloids. Histological observations further indicated a higher abundance of secretory structures in semi-double flowers, suggesting an anatomical basis for enhanced metabolite storage. Among the examined varieties, the orange semi-double type consistently displayed the highest phytochemical levels across tissues. These results suggest a coordinated shift in resource allocation from structural support toward secondary metabolism associated with floral architectural modification. By linking floral form with internal anatomy and chemical investment, this study advances current understanding of trait integration in C. sulphureus and provides a framework for the selection of germplasm with enhanced phytochemical potential.