A gametophyte development stage (PO:0028003) during which the megagametophyte (PO:0025279) develops. [source: POC:curators, POC:Laurel_Cooper]
Comment
Although megaspore and megagametophyte development are normally separate, one spore producing one gametophyte, in some flowering plants a single gametophyte may be produced from two or four spores.