A fern is a type of plant with about 12,000 species known.
Like mosses they also bear xylem and phloem.
They also bear roots, stems and leaves like other vascular plants but they lack flowers and seeds.
They produce spores.
The largest group of ferns known include leptosporangiate ferns.
The common examples are horsetails, whisk ferns, marattioid ferns, and ophioglossoid ferns.
The term pteridophyte also refers to ferns.
A pteridologist studies about ferns and lycophytes.
Fossil record suggests that they evolved 360 million years ago in the Carboniferous period but majority of the living ferns are about 145 million years old which evolved in the Cretaceous.
They are not very important from the commercial point of view but are grown for ornamentation, food or remediating soils.
Some are weeds and some hold special place in mythology, culture and art.
Ferns are vascular plants differing from lycophytes by having true leaves.
They differ from gymnosperms and angiosperms in lacking seeds and flowers but bear spores.
Their life cycle shows alternation of generation which means it consists of diploid sporophytic and a haploid gametophytic phase.
A sporophytic phase produces haploid spores by meiosis.
A spore grows by mitosis and produces gametophyte which develops photosynthetic prothallus.
Gametophyte produces gametes by mitosis.
A mobile, flagellated sperm fertilizes the egg which is attached to the prothallus.
A zygote which is now diploid produces sporophyte by mitosis.
They prefer to live in a wide variety of habitats ranging from remote mountain elevations, to dry desert rock faces, to bodies of water or in open fields.
In general terms they prefer four types of habitats namely moist, shady forests; crevices in rock faces, especially when sheltered from the full sun; acid wetlands including bogs and swamps; and tropical trees, where many species are epiphytes.
Many are known to develop associations with mycorrhizal fungi.
The spores are rich source of lipids, protein and calories so are consumed by some animals.
The stem is usually a underground rhizome but in some cases it is a ground creeping stolon or semi-woody tree trunk.
The leaves are green and photosynthetic and are known as fronds because of their horizontal arrangement.
The leaves are of three types.
Tropophylls participate only in photosynthesis like the leaves of other vascular plants.
Sporophylls produce spores and compared with the scales of pines.
They also photosynthesize like tropophylls.
Brophophylls produce abnormally large number of spores.
The roots are underground and non-photosynthetic.
They are fibrous similar to other vascular plants.
Prothallus is green, photosynthetic structure generally one cell thick.
It is heart of kidney shaped measuring 3-10 mm long and 2-8 mm broad.
It produces gametes in the form of antheridia and archegonia.
Anteridia are small spherical structures that produce flagellated sperms.
Archegonia are flask-shaped structures that produce single egg.
Rhizoids are root like structure that absorbs water and minerals.
They anchor prothallus to soil.