Archegonium
An archegonium (plural archegonia) is an organ of the gametophyte generation of a plant responsible for producing the ovum (female gamete). Archegonia are external and may be observed microspically in seedless plants. It is reduced and embedded within the gametophyte in gymnosperms.They do not exist in angiosperm and the gnetophytes Gnetum and Welwitschia. Other than the egg it contains, the organ itself is sterile (incapable of sexful activities). This is a consequence of their different ploidy. As part of the gametophytic parent tissue, archegonium is diloid, but the gamete is haploid.
The egg is stationary, so it is encased inside archegonium until its growth protuding outward after fertilization.
The corresponding male organ is called the antheridium.