Ferns are among the most primitive types of plants in that they reproduce through the dispersion of spores instead of seeds like more evolved plants. Ferns are traditionally considered plants of moist shaded woodlands, but they have adapted to many different kinds of habitats from mountain heights to rocky desert areas. They often grow where flowering, seeding plant cannot survive. The life cycle of ferns require the formation of a totally distinct form with a different number of chromosomes.
The Mature Fern Phase
Reproduction in ferns must always start with a mature fern plant. At maturity, the plant has sporangia, which are structures that produce the spores. These form on the underside of the fronds. The sporangria form into aggregates that form a sort of line that can be seen with the naked eye under the frond.
The Spore Phase
The cells within the sporangia undergo a process called meiosis, which reduces the number of chromosomes in the spore cells. This reduction of chromosomes allows the formation of separate male and female reproductive cells. The spore cells are then released into the wind and land on suitable areas. They then grow into another, individual form of the plant, the gametophyte.
The Gametophyte Phase
The spores develop into a flat, thin, heart or kidney shaped plant called a gametophyte. Gametophytes are individual plants that do not posses leaves, stems or roots, but they do have rhizoids that anchor them into place and help them absorb moisture and nutrients. The gametophyte produces both sperm and egg cells that will fertilize each other or other fern plant cells in the area. The male reproductive organ that produces sperm cells is called the antheridium. The female organ is called the archegonium. These reproductive organs produce the cells that join together to create new fern plants. The presence of water is necessary for the fertilization process to occur, which is why ferns are so likely to be found in wet habitats.
Tiny, New Fern Plants
The fertilized cells grow into small, delicate ferns that are in the shape of shepherd’s crooks, with curled tops. These tiny crooks uncurl from a moss-like bed that grows from the joining of the male and female cells produced by the gametophyte plant. These plants must grow larger in order to survive. If exposed to too much sunlight, they can die, preventing the establishment of new ferns to replace the older plants. If conditions are right, the tiny, crook-headed plants continue to grow into strong, mature fern plants that bear sporangia for making new spores to create more plants.