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Stem anatomy and modulus of elasticity (MOE) were compared between upright and trailing cultivars of periwinkle [Catharanthus roseus (G.) Don.]. The inheritance of growth habit and flower form was also studied. Internode cross sections revealed that phloem fiber was distributed at the inner cortex in upright cultivars but not in trailing cultivars. Except the youngest internode, the upright ‘Vitesse Pink’ had the highest MOE throughout the 1st–13th internodes above the cotyledon. The more trailing ‘Cora Cascade Strawberry’ had consistently lower MOE than a less trailing ‘Cora Cascade Polka Dot’. All F1 plants between upright and trailing cultivars were upright, and the F2 generation derived from self-pollinating F1 fit a 3 upright : 1 trailing segregation ratio. All F1 plants between upright/double-flower and trailing/single-flower exhibited upright and single-flowers, whereas plants in the F2 generation fitted a 9 upright/single-flower : 3 trailing/single-flower : 3 upright/double-flower : 1 trailing/double-flower ratio. New double-flowered periwinkle selections with trailing growth habit were successfully developed from the F2 population.