A whole plant (PO:0000003) in the gametophyte development stage (PO:0028003) that produces plant sperm cells (PO:0000084). [source: POC:curators]
Comment
The microgametophyte in bryophytes only produce sperm cells, but do not develop from microspores, because there is no heterospory in bryophytes. In seed plants the male gametophyte is reduced to a pollen grain.