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Simaroubaceae is a monophyletic family in the order Sapindales with 22 genera and 109 species. Ailanthus altissima (Mill) Swingle, also known as the tree of heaven, is a highly invasive species, which systematically belongs to Simaroubaceae. Reproductive characteristics are essential for the deployment and maintenance of invasive species in new environments and examination of the reproductive system of these species is interesting. To date, no embryological investigations had been directed to A. altissima and our knowledge on the embryology of this species was very limited. A study was carried out on the embryology of A. altissima and the comparison of anther development in male and female flowers in order to gain insights into defining embryological features in this species. According to the results of histological analysis, male flowers have rudimentary gynoecia and anthers are tetrasporangiate. Cytokinesis in meiosis is simultaneous resulting in tetrahedral tetrads. Anther wall development follows the dicotyledonous type and the tapetum is secretory. Female flowers have staminodes and microspore mother cells are degraded too early before entering the course of meiosis. Ovules are anatropous, bitegmic, and crassinucellate. The development of the embryo sac follows the polygonum type. Embryos follow the Onagrad type. The endosperm development is nuclear type. A well-developed hypostase is present and a nucellar cap is formed. These observations will advance our understanding of embryology and embryo anatomy in A. altissima as an invasive species.