, Volume 33, Issue 6, pp 1571–1582 | Cite as

Floral development and the formation of functionally unisexual flowers in Xanthoceras sorbifolium (Sapindaceae), a morphologically andromonoecious tree endemic to northern China

  • Qingyuan ZhouEmail author
  • Qing Cai
  • Yuanrun Zheng
  • Zhiyan Wu
  • Jianfeng Mao
Original Article


Key message

Xanthoceras sorbifolium is apparently andromonoecious but exhibits a cryptically monoecious breeding system. Sexual differentiation in male and functional female flowers occurs 2 weeks before flowering.


Individual trees of Xanthoceras sorbifolium bear male and morphologically bisexual flowers but functionally female flowers, and show labile sex expression. Investigations of the floral development are of significant value for understanding the breeding system and elucidating the systematic relationships. We studied floral development of male and bisexual flowers using scanning electron and light microscopy. The early stages of floral development were essentially the same, and all floral organ primordia were initiated in the two types of flowers of X. sorbifolium. Later, the stamens in bisexual flowers and the gynoecium in male flowers were aborted. We divided floral development into nine stages. Morphological differences between male and bisexual flowers appeared first at stage 8, when the style elongated obviously and the stigma papillae began to expand in the bisexual flowers but not in the male flowers. Ovule development was arrested shortly after formation of megaspore mother cells or during meiosis in the male flowers, whereas anther development was aberrant in the bisexual flowers. Morphologically bisexual flowers of X. sorbifolium do not have male function and are functionally female. Comparison of floral developmental characters did not support the separation of the Chinese monotypic genus Xanthoceras from the family Sapindaceae.


Floral development Andromonoecy Monoecy Systematic relationship Xanthoceras sorbifolium 



We would like to thank Xiuping Xu, Jie Wen, and Fengqin Dong for technical help. This work was supported by National Natural Science Foundation of China (30972344, 31370611 and 31570680) and Beijing Natural Science Foundation (6172028).


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Key Laboratory of Plant Resources, Institute of BotanyChinese Academy of SciencesBeijingChina
  2. 2.Shinyleaf Yellowhorn Engineering and Technology Research Center of National Forestry and Grassland AdministrationChifengChina
  3. 3.College of Biological Sciences and TechnologyBeijing Forestry UniversityBeijingChina

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