Mosses are part of a group of non-vascular plants called Bryophytes. Bryophytes include liverworts, hornworts, and mosses. Bryophytes have an Alternation of Generations life cycle. This includes the gametophyte (haploid) mossy stage and the sporophyte (diploid) archegonium stage. The haploid form is the long-lived stage in these organisms. Moss gametes (egg and sperm) fuse to develop a zygote. This develops into a sporophyte that grows an archegonia. The archegonia produces male and female spores that disperse and grow into new moss.
Archegonia are seen here growing at the top out of the moss.