Abstract:The megasporogenesis, megagametophyte and embryo development in Flaveria bidentis (L.) Kuntze were observed by using paraffin section method. The results showed that the stigma had 2 split, ovary was unilocular with bicarpellate, one ovule, basal placenta, unitegmic, tenuinucellate, anatropous ovule, and developed integumentary tapetum. Archesporial cell differentiated below the nucellar epidermis developed into megaspore mother cell, which formed a linear tetrad by meitotic divison, one megaspore at micropylar end developed into a functional megaspore, and the others degraded. The development of embryo sac was Monosporic Type. The mononucleate embryo sac underwent three successive mitosis to form mature embryo sac with seven cells, egg cell and two synergids near the micropyle, a binuclear central cell in the center of embryo sac, three antipodal cells in the chalazal. The embryo development could be divided into four stages, such as globular embryo, heart-shaped embryo, torpedo embryo and mature cotyledon embryo. The development of the endosperm was Cell Type, and that of embryo belonged to Asterad Type. The mature seed had an endosperm jacket layer, and the secretory structure and secretions were observed in seed capsule, placenta and bract.