An archegonium (pl: archegonia), from the ancient Greek αρχη (beginning) and γονος (offspring), is a multicellular structure or organ of the gametophyte phase of certain plants producing and containing the ovum or female gamete. The archegonium has a long neck and a swollen base. Archegonia are typically located on the surface of the plant thallus, although in the horned liverworts they are embedded.

They are also much-reduced and embedded in the megasporangium of gymnosperms. The term is not used for angiosperms or the gnetophytes Gnetum and Welwitschia because the comparable "structure" is reduced to just a few cells, and the function of surrounding the gamete is completely assumed by diploid cells of the megasporangium.

The corresponding male organ is called the antheridium.

Plant anatomy | Cryptogams | Gymnosperms | Plant reproduction

Archegonium