Fern

Ferns are considered some of the oldest land plants on earth, dating from 200 million years ago. Ferns are cryptogamous, or spore-producing, plants. Found worldwide, ferns are capable of growing in soil, water, on rocks, or on other plants. They range in size from a few centimetres to nearly 24 m (80 ft) in height. The underground stems and the fronds, or leaves, of some fern plants are edible.

Dorling Kindersley

Underside of a Fern Frond Showing Ripe Sori

An examination of the underside of a fern frond reveals small, spore-bearing structures called sori. When the sori become mature, they split open and release thousands of minute spores. Under favourable conditions, the spores germinate and grow into small, heart-shaped plants called prothalli. The prothalli produce ''eggs'' and ''sperm'', and, following fertilization, a new fern plant called the sporophyte begins to grow.

Harold Taylor/Oxford Scientific Films

Alternation of Generations

Ferns’ mode of reproduction includes what is called alternation of generations. The mature fern plant, the sporophyte stage, is the generation that produces spores. The spores are released into the air and subsequently settle and germinate into a small, usually inconspicuous generation called the gametophyte stage. This stage produces male and female gametes, which fuse and grow into a new sporophyte stage.

Dr. C.E. Jeffree/Oxford Scientific Films

Maidenhair Fern

The maidenhair fern, Adiantum capillus-veneris, a deciduous fern found in termperate and subtropical areas worldwide, is characterized by arching, light green fronds borne on black stems. It reaches a height of 30 cm (12 in). The maidenhair fern grows best in shaded locations with moist soils.

Dorling Kindersley

Soft Shield Fern

The soft shield fern, Polystichum setiferum, is cultivated for its attractive, soft-textured foliage. This species of fern grows to a height of 60 cm (24 in). Ferns have become popular domestic plants, displaying a wide variety of sizes, colours, and textures while being relatively easy to grow.

Geoff Kidd/Oxford Scientific Films

Life Cycle of a Fern

On the underside of the leaves, groups of spore cases, or sporangia, form. They are seen as small brown spots, known as sori. The spore falls and begins to germinate, developing into a gametophyte called the prothallus. On the underside of the prothallus are the female sexual organs (archegonia) and the male sexual organs (antheridia). Fertilization of the eggs in the archegonium takes place only in the presence of water. Only one sporophyte plant develops from each prothallus. The parent prothallus then dies.

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