Ferns fall into a category called "vascular plants without seeds." In addition to having no seeds, ferns do not produce flowers. They reproduce through spores and have a unique life cycle. Though ferns can be found in drier areas, they are usually found in moist regions. Ferns rely on moisture to complete their reproductive cycle. In the absence of rain or dew some ferns can remain dormant for up to five years. When moisture is again available, they will resume their life cycle. A small group of dry-land ferns are the exception.
Capsules called sori develop on the underside of mature fern fronds. The capsules are generally round but can be urn, kidney or rectangular in shape. The sori are usually brown in color and some have tiny brown hairs. A type of cell division (meiosis) occurs in the sori resulting in both male and female cells. At this point the spores become dry and blow away to their new destination.
The spore cells germinate and develop into a heart shaped structures called gametophytes. The gametophytes mature and develop into prothallium. This intermediate stage of growth is what sets a fern's life cycle apart from the common seed producing plants. In seed producers, this phase does not exist.
At the prothallium stage the developing fern can begin to photosynthesize. The prothallus are able to anchor to the ground with root-like structures. This is when fertilization will occur, but only in the presence of moisture. This usually comes in the form of rain or dew. The sperm swim to the female eggs and fertilize them. Though both male and female organs are close together they often mature at different times. For this reason a sperm from one prothallus will often swim to another prothallus and fertilize a more mature egg. When spermatazoa and ova fuse together they become one structure called a zygote.
The maturing zygote then develops into an embryo. The embryo contains everything that is needed to develop into a new fern plant. As the fern becomes more independent, the prothallus dies.
A sporophyte is a tiny fern plant. This is the phase when little leaf fronds begin forming. It is a small fern without its reproductive parts. It is far more prone to moisture loss at this stage and will easily succumb if it becomes too dry.
The following spring the young fern will develop new growth called fiddleheads. These are young delicate coiled fronds. Most fern fronds will reach maturity by the end of the growing season. In most regions this will be in the fall.
The maturing ferns will once again develop little sacs or sori underneath the fronds. They will be filled with new spores ready to start the life cycle all over again. Some spores blow to other areas, while some fall close by. This is how fern groves develop.