Following meiosis in the megaspore mother cell, four haploid megaspores are formed. In the common Polygonum-type development, three of these megaspores degenerate, while the remaining chalazal megaspore continues to develop into the functional female gametophyte or embryo sac.

In angiosperms, the ovules are borne on modified leaves known as carpels or megasporophylls. These are considered fertile structures because they are directly involved in the reproductive process, leading to the formation of seeds after fertilization occurs within the ovary.

In the life cycle of seed plants, the megaspore (haploid) undergoes mitotic divisions to develop into the female gametophyte, also known as the megagametophyte or embryo sac in angiosperms.

In heterosporous plants, megaspores are the larger type of spores produced by the megasporangium. They are typically female gametophyte precursors and are significantly larger in size compared to the microspores, which are the smaller, male-producing spores. This size difference is a fundamental characteristic in the evolution of heterospory in plants.

The ovule is the precursor to the seed in seed plants. It consists of the nucellus, which is the central mass of nutritive tissue, protected by one or two layers called integuments. These integuments eventually develop into the seed coat after fertilization occurs, providing protection to the developing embryo inside.

In the ovule, a specific cell within the nucellus differentiates and enlarges to become the megaspore mother cell. This cell undergoes meiosis to produce megaspores, one of which eventually develops into the embryo sac, or the female gametophyte, in angiosperms.

The funicle is a slender, stalk-like structure that connects the ovule to the placenta within the ovary. It serves as a conduit for vascular tissues, ensuring that nutrients and water are transported from the parent plant to the developing ovule and embryo.

Integuments are the protective outer coverings of the ovule. Most angiosperms have two integuments (bitegmic), while some have one (unitegmic). These layers eventually develop into the seed coat (testa and tegmen) after fertilization, providing protection to the embryo inside the seed.

The micropyle is a small pore or opening in the integuments of an ovule through which the pollen tube typically enters during fertilization. It is a critical feature for the successful fusion of male and female gametes in angiosperms.

The functional megaspore is the first cell of the female gametophyte. Following meiosis in the megaspore mother cell, the surviving megaspore undergoes mitotic divisions to develop into the mature embryo sac, which represents the female gametophyte generation.