Morphological and anatomical changes during floral bud development of the trioecious Idesia polycarpa Maxim

Idesia polycarpa Maxim is described as a dioecious species, in which flowers are female or male, but we have also found individuals with bisexual flowers. The study aimed to provide the theoretical basis for the artificial control on flowering, fruiting, and floral initiation of Idesia polycarpa Maxim species. The morphological and anatomical structure of female, male, and bisexual flowers of I. polycarpa was studied. In this study, the routine paraffin section and morphological observation methods were used. The flowering of I. polycarpa began in late July. Results showed that the short-branch terminal bud was the highest percentage of floral bud position both in the female and male plants compared to the other bud types, and the proportion was 68.6% and 76.3%, respectively. Evidence from floral structural analysis suggests that the female and male flowers of I. polycarpa are unisexual by abortion. The ovary of the male flower stops developing after the ovule primordium initiation. The female, male, and bisexual flowers of I. polycarpa had the same anatomical structure at the beginning of development, but differences emerge in the differentiation stage of the female and male. In the bisexual flowers, females and males develop normally and may produce fruits. The study suggests that the bisexual, male, and female flowers were produced on the separate plants of the same species; therefore, the species is trioecious.