Inflorescence development in Hydrangea macrophylla

The inflorescence development process in the Hortensias of Hydrangea macrophylla was compared with that in the Lacecaps of H. macrophylla using scanning electron microscopy. During the early stages of inflorescence development, the apical meristem produced pairs of partial inflorescence primordia successively as axillary buds on the primary inflorescence apex. During the latter developmental stage, in Lacecaps, the axillary primordia initiated on each inflorescence apex, developed into inflorescences. However, in the Hortensias, the axillary primordia developed into decorative florets. In both of them, terminal florets which were non-decorative were initiated from the apical meristem on main and partial inflorescence apices. In H. macrophylla 'Renata' (the Hortensias), a bud mutant in which most axillary buds of the main inflorescence axis developed into decorative florets was found. The composition and the development process of inflorescence in the mutant represented a simple raceme.