A plant organ (PO:0009008) that produces one or more gametes (PO:0025006) and participates in the gametophyte development stage (PO:0028003). [source: POC:curators]
Comment
The multicellular plant gametangium; an archegonium (PO:0025126) and/or an antheridium (PO:0025125), occurs in bryophytes, pteridophytes and gymnosperms, but never in angiosperms.