The life cycles of mosses and ferns are similar. They share the characteristic of being nonflowering plants. But like virtually all plants--flowering or nonflowering--mosses and ferns can reproduce both sexually and asexually. A piece of an existing moss or fern plant can break free from the existing plant and establish a new plant. This is asexual reproduction and forms a clone of the parent plant.
In both mosses and ferns, in the absence of flowers and seeds, sexual reproduction occurs by means of spores. The spore-bearing structure is termed a sporangium. It is generally tiny and club-shaped or capsule-shape. In a typical fern, the sporangia are clustered into groups which are covered and protected by an umbrellalike feature. In many ferns this arrangement of reproductive structures is on the underside of the leaf or leaflet. In contrast, the moss sporangia simply grow upward from a thin stalk.
One phase of the life cycle in both mosses and ferns serves to carry out sexual reproduction. In mosses it is the obvious part of the plant that we recognise as the moss plant. In ferns, on the other hand, this phase of the plant's life cycle is tiny and usually hidden by dead leaves and other debris. The casual observer is extremely unlikely to ever see it.
In contrast to the small and inconspicuous stage of sexual reproduction, the fern's alternate stage is the relatively large plant that we recognise as the fern. It is this stage that bears spores. In ferns the two different stages exist as physically separate individuals.
In a typical moss plant, the green mossy part of the plant is the sexually reproducing stage. From it stalks grow that produce and contain the spores. In contrast to ferns, in mosses the two stages--the sexually reproducing stage and the spore-bearing stage--grow together as part of the same plant.
Both mosses and ferns produce spores that contain half the number of genes present in the plant as a whole. When the spores germinate, they grow and develop into the sexually reproducing stage of the plant. During sexual reproduction, sperm and egg unite resulting in the spore-bearing stage of the plant. Again, in both mosses and ferns the spore-bearing stage has the full genetic complement. It is during spore production that the number of genes is divided in half once again.
As the fern sporophyte grows into the plant we recognise as a fern, it produces a rootstock or rhizome that is generally semihorizontal. From this rhizome grows the fern frond or leaf above, and the roots below. Although the moss plant has small rootlike structures, it lacks the rhizome featured in the fern.