Replacement of the normal sexual reproduction by asexual reproduction without fertilisation is called apomixis, e.g. replacement of the flower by bulbils and replacement of the seed by a plant.
Apomictically produced offsprings are genetically identical to the parent plant. In flowering plants, apomixis is used in a restricted sense to mean angiosperm, i.e. asexual reproduction through seeds. In some plant species it is common, e.g. Asteraceae and Poaceae. In some species, the diploid egg cell is formed without reduction division and develops into embryo without fertilisation. It is an asexual reproduction in the absence of pollinators such as in extreme environments. In some species like Citrus, some of the nucellar cells surrounding the embryo sac start dividing and develop into embryo. It occurs in the megaspore mother cell and does not undergo meiosis, thus produces diploid embryo sac through mitotic divisions. Thus, it explains that, embryo sacs of some apomictic species appear normal but produce diploid cells.