Plant gametangium was part of the existing tracker for archegonium, antheridium, and gametangium (https://sourceforge.net/tracker/index.php?func=detail&aid=3109542&group_id=76834&atid=835555), but I think it needs to be in a separate tracker to prevent confusion.
Existing def'n from POC meeting on 3-22-11, plus meeting between DWS, MAG and RLW:
plant gametangium (PO:0025124): A plant organ that produces one or more gametes that are located in it and is part of a whole plant in the
participates in gametophytic phase, only_in_taxon bryophytes plus pteridophytes plus gymnosperms (=never_in_taxon angiosperms)
Comment: The embryo sac and pollen replace the function of gametangia of producing gametes in gymnosperms (for antheridia) and angiosperms (for both
antheridia and archegonia).
(This definition of gametangium works for algae. Could add a child term oogonium.)