Fern, any of more than 6,000 species of perennial, flowerless plants found in various parts of the world. As a general rule they are of largest size and are most numerous in damp tropical islands. In Hawaii, New Zealand, and Japan there are huge ferns known as tree ferns. Tree ferns have erect, unbranched stems with a crown of palmlike leaves and grow to 75 feet high. The leaves grow from stems, not rootstocks. On the other band, there are some ferns not much larger than mosses.
The leaf of the fern is known as the frond. It grows directly from the rhizome, which is an underground stem. This stem bears adventitious roots. The fern does not have flowers or seeds but instead bears small bodies, called spores, that serve as seeds, that is, the spores produce new plants. The brown dots on the underside of the fronds are sori, or structures that contain the spore cases, the sporangia, which are filled with spores.
The new plants from spores are not the usual fern plants with the characteristic fronds. Spores give rise to the gametophyte (sexual) generation, often a small, heart-shaped, flat structure on which are developed the male and female sex structures, the antheridia and archegonia. When a sperm from the antheridium unites with an egg in an archegonium, a zygote results; it, in turn, develops into the usual fern plant, the sporophyte (asexual) generation.
There are many varieties of ferns in the woods that are familiar to us. Some of these are also in gardens, usually doing best in damp, shady places. The Boston fern, the maidenhair fern, the holly fern, and others are common house and greenhouse plants. The ferns are among the oldest of our plants, dating from the time when coal was being formed over 300,000,000 years ago.
