whole plant plant embryo A plant embryo is generally formed after the first division of a plant zygote (PO:0000423), but in the case of a nucellar (adventitious) plant embryo (PO:0004537), somatic plant embryo (PO:0025302), microspore-derived cultured plant embryo (PO:0025305), and other embryos that arise through apogamy, it begins after the division of a single cell that is not a zygote. The end of the embryo stage varies among taxa; the beginning of a seed germination stage (PO:0007057) in seed plants, formation of the first vascular leaf (PO:0009025) in pteridophytes, the beginning of development of a sporangium (PO:0025094) in bryophytes, or the beginning of the formation of a plant organ (PO:0009008) such as a root (PO:0009005), shoot axis (PO:0025029), or vascular leaf (PO:0009025) in a cultured plant embryo (PO:0000010).