The produce by tiny dust like spores their spores grow on the underside of their leaves.
Ferns reproduce through their spores, which are produced in very small spots called sori. Each sorus consists of numerous tiny, spherical granules that contain sporangia. Once the sporangia mature, they burst and release spores into the wind, and this is how new ferns emerge.
With the right environmental conditions, the spores will be carried to new areas where they germinate and form fern prothallus. A fern has a leafy branch called a frond, which consists of smaller leaflets known as pinnae. There are tiny spots under a frond where spores grow inside casings referred to as sporangia. These sporangia form a sorus, which sometimes exist on the veins of a fern leaf. They are also sometimes found under the pinnae. Not all fronds contain spores. Fronds with spores are known as fertile fronds. Through a circuitous process, a spore can grow into an adult fern. It needs the right conditions to grow into a plantlet called gametophyte or prothallus.
Spores behave like a seed, although a full adult plant is what grows from the seed. The prothallus grows from a spore. It is not the full fern, as it is the intermediate phase from a spore into an adult fern. New ferns only grow in a moist environment. They fertilize and transform into a complete adult plant when there is enough moisture. They then turn into a sporophyte that continues to grow into a complete adult fern that is capable of producing its own spores, thus repeating the life cycle.