Periwinkle [Catharanthus roseus (L.) G. Don] is renowned for its diverse colors and resilience to harsh climates. Still, most commercial cultivars predominantly display flat petals, lacking in ornamental variety. Diversifying flower forms can not only enhance its aesthetic appeal, but also potentially impact market dynamics. With this backdrop, our study embarked on elucidating the inheritance patterns of wavy flower forms, aiming to refine periwinkle breeding strategies. Using cultivars with non-wavy, medium-wavy, and extreme-wavy flower forms, we examined differences in both their leaf and floral organs. Phenotypes of self-pollinated (S₁) and cross-pollinated (F₁, F₂) populations further underscored their morphological distinctions. Specifically, the extreme-wavy type displayed elliptical leaves, broader than the non-wavy type, with pronounced pointy tips and a notably wrinkled surface. This type also bore intensely wavy petal margins and exhibited a smaller flower diameter, with a notable absence of typical pistils, indicating female sterility. Insights gained allowed early differentiation during the seedling period. Our findings suggest that the inheritance of these flower forms is regulated by an allele WAVY (Wv), which exhibits incomplete dominance. Specifically, the non-wavy form arises from a recessive homozygous expression (wvwv), the extreme-wavy form arises from a dominant homozygous expression (WvWv), and the medium-wavy form arises from a heterozygous expression (Wvwv). This study provides clarity on inheritance patterns, facilitating the strategic breeding of diverse flower forms in periwinkle.