How do ferns reproduce without flowers or seeds?

Ferns reproduce through a process known as alternation of generations, which involves two distinct life stages: the sporophyte and the gametophyte.12

The Life Cycle

• Sporophyte Stage: The large, leafy plant typically recognized as a fern is the sporophyte. It produces spores within specialized structures called sporangia, which are often clustered in groups known as sori on the undersides of the fronds.123
• Gametophyte Stage: Once released and dispersed by wind, a spore may germinate in a suitable environment to grow into a tiny, heart-shaped plant called a prothallium. This gametophyte is the sexual phase of the plant.132
• Fertilization: The prothallium produces male (antheridia) and female (archegonia) sex organs. Sperm swim through water to reach and fertilize the egg. The resulting zygote develops into a new, independent sporophyte, eventually causing the small prothallium to wither and die.321

Additionally, many ferns can reproduce vegetatively through their underground stems, or rhizomes, allowing them to form large colonies.1