A fern is a type of plant with about 12,000 species known. They also bear roots, leaves and stalks like other vascular plants but they lack flowers and seeds. They produce spores. The biggest group of ferns known include leptosporangiate ferns.
The expression pteridophyte also refers to ferns. A pteridologist studies about ferns and lycophytes. Fossil record suggests that they evolved 360 million years back in the Carboniferous period but vast majority of the living ferns are about 145 million years old which evolved in the Cretaceous. They are not so significant from the commercial point of view but are grown for ornamentation, food or remediating soils. Some are weeds and a few hold special place in mythology, culture and art.
Ferns are vascular plants differing from lycophytes by having leaves that are true. They differ from gymnosperms and angiosperms in lacking seeds and blossoms but bear spores. Their life cycle reveals alternation of generation which means it is composed of diploid sporophytic and a haploid gametophytic stage. 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 currently diploid produces sporophyte by mitosis.
They prefer to stay in a wide variety of habitats ranging from distant mountain elevations, to arid desert stone faces, to bodies of water or in open fields. Generally 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 relationships with mycorrhizal fungi. The spores are rich supply of lipids, protein and carbs are consumed by some animals. The stem is usually a underground rhizome but in some cases it’s a ground creeping stolon or semi-woody tree trunk. The leaves are green and photosynthetic and are called fronds because of their horizontal arrangement. Tropophylls participate only in photosynthesis like the leaves of other vascular plants. Sporophylls produce spores and compared with the scales of pines. In addition they photosynthesize like tropophylls. Brophophylls produce abnormally large number of spores. The roots are underground and non-photosynthetic. They are fibrous like 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 wide. It produces gametes in the kind of antheridia and archegonia. Anteridia are small spherical structures that produce flagellated sperms. Archegonia are flask-shaped structures which produce single egg. Rhizoids are root like structure that absorbs water and minerals. They anchor prothallus to dirt.