macrosporangium

A macrosporangium is a structure found in plants that produces megaspores. In seed plants, the macrosporangium is also called the ovule. The megaspore develops into a female gametophyte, which produces egg cells. In gymnosperms, the macrosporangium is a nucellus surrounded by one or two integuments. In angiosperms, the ovule consists of the nucellus, one or two integuments, and a female gametophyte called the embryo sac. The embryo sac is typically eight-nucleate and seven-celled, containing an egg cell, two synergids, three antipodal cells, and a central cell with two polar nuclei. After fertilization, the ovule develops into a seed.

The development of the macrosporangium is initiated by the formation of a megaspore mother cell within the nucellus. This diploid cell undergoes meiosis to produce four haploid megaspores. Typically, only one megaspore survives and develops into the female gametophyte. The rest degenerate. In angiosperms, the embryo sac develops from a single megaspore through mitotic divisions. The structure and organization of the macrosporangium are crucial for the reproductive success of plants, as it houses and protects the female gametes and eventually develops into the seed. Variations in macrosporangium structure and development exist across different plant groups, reflecting their evolutionary divergence.