Comparison of Inflorescence Composition and Development in the Lacecap and its Sport, Hortensia Hydrangea macrophylla (Thunb.) Ser.

The composition and development of inflorescences were compared between a lacecap and hortensia Hydrangea macrophylla(Thunb.) Ser. In this study, we used 'Blue Sky' cuttings as lacecap plants and mutated branch cuttings as hortensia plants. The only difference between the inflorescences of lacecap and hortensia was the structure of the upper nodes near the terminal flowers. Partial inflorescences set on the upper nodes of the lacecap, whereas decorative flowers set on the upper nodes of the hortensia. The basic developmental process of the inflorescence was similar in both the lacecap and hortensia. Several pairs of axillary primordia were successively initiated on the inflorescence primordia that were followed by the initiation of terminal flowers. These terminal flowers developed as non-decorative flowers, whereas most axillary primordia developed into partial inflorescences. In hortensia, however, the axillary primordia at the upper nodes differentiated into decorative flowers, which indicates that the change in the inflorescence structure during the mutation from lacecap to hortensia is the replacement of partial inflorescences with decorative flowers on the upper nodes of the inflorescence axes.