Fern

Fern is a common name for a group of vascular plants in the class Polypodiopsida that reproduce by spores rather than seeds. Ferns have true vascular tissue and megaphyll leaves called fronds, which typically arise from underground stems called rhizomes. The fronds often uncoil as fiddleheads, a characteristic called circinate vernation. Most ferns are homosporous, producing one type of spore on the undersides of the fronds at clusters called sori.

Ferns undergo alternation of generations. The spore germinates into a small, free-living gametophyte called a prothallus that bears both sperm-producing antheridia and egg-producing archegonia. When water enables sperm to swim to an archegonium, the zygote grows into a new diploid sporophyte, the familiar fern plant. In some aquatic ferns, the life cycle includes distinct, larger heterosporous stages, but this is less common.

Ferns inhabit a range of environments, from tropical forests to temperate woodlands, rocky outcrops, and wetlands. They often prefer moist shade but are adapted to a variety of habitats, including epiphytic life on trees. Ecologically, ferns contribute to ground cover, prevent erosion, and provide habitat for invertebrates. They are widely cultivated as ornamentals and some species, such as the ostrich fern (Matteuccia struthiopteris), are harvested for edible fiddleheads after cooking. Some ferns are considered invasive in certain regions, such as Pteridium aquilinum (bracken). The fossil record shows ferns are among the earliest surviving vascular plants, with a long evolutionary history dating back to the Devonian.