Comparison of decorative and non-decorative flowers in Hydrangea macrophylla (Thunb.) Ser

A comparison was made between decorative and non-decorative flowers in Hydrangea macrophylla. The external appearance of petals, stamens, and pistils were similar in both types of flowers. The locules and placentas of the decorative flower were smaller than those of the non-decorative flower. On the other hand, the decorative flower’s receptacle was much more developed than that of the non-decorative flower. In the development of ovules, no differences were obvious between both types of flowers. There were no significant differences in pollen fertility between both types of flowers as estimated by germination tests and acetocarmine staining tests. Pollen from both flower types functioned normally to produce germinable seeds in controlled pollination tests. Both types of flowers showed female fertility in open pollination tests. The non-decorative flowers were pentamerous, whereas most decorative flowers were tetramerous. These results which revealed the differences between decorative and non-decorative flowers will help to elucidate the mechanism of decorative flower formation.