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Uses

Ferns are not as important economically as seed plants, but have considerable importance in some societies. Some ferns are used for food, including the fiddleheads of Pteridium aquilinum (bracken), Matteuccia struthiopteris (ostrich fern), and Osmundastrum cinnamomeum (cinnamon fern). Diplazium esculentum is also used in the tropics (for example in budu pakis, a traditional dish of Brunei) as food. Tubers from the "para", Ptisana salicina (king fern) are a traditional food in New Zealand and the South Pacific. Fern tubers were used for food 30,000 years ago in Europe. Fern tubers were used by the Guanches to make gofio in the Canary Islands. Ferns are generally not known to be poisonous to humans. Licorice fern rhizomes were chewed by the natives of the Pacific Northwest for their flavor. Some species of ferns are carcinogenic, and the British Royal Horticultural Society has advised not to consume any species for health reasons of both humans and livestock.

Ferns of the genus Azolla, commonly known as water fern or mosquito ferns are very small, floating plants that do not resemble ferns. The mosquito ferns are used as a biological fertilizer in the rice paddies of southeast Asia, taking advantage of their ability to fix nitrogen from the air into compounds that can then be used by other plants.

Ferns have proved resistant to phytophagous insects. The gene that express the protein Tma12 in an edible fern, Tectaria macrodonta, has been transferred to cotton plants, which became resistant to whitefly infestations.

Many ferns are grown in horticulture as landscape plants, for cut foliage and as houseplants, especially the Boston fern (Nephrolepis exaltata) and other members of the genus Nephrolepis. The bird's nest fern (Asplenium nidus) is also popular, as are the staghorn ferns (genus Platycerium). Perennial (also known as hardy) ferns planted in gardens in the northern hemisphere also have a considerable following.

Several ferns, such as bracken and Azolla species are noxious weeds or invasive species. Further examples include Japanese climbing fern (Lygodium japonicum), sensitive fern (Onoclea sensibilis) and Giant water fern (Salvinia molesta), one of the world's worst aquatic weeds. The important fossil fuel coal consists of the remains of primitive plants, including ferns.