A fern is a sort of plant with about 12,000 species known. Like mosses they also bear xylem and phloem. They also bear roots, leaves and stalks 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 research about ferns and lycophytes. Fossil record suggests that they evolved 360 million years ago in the Carboniferous period but majority of those living ferns are about 145 million years old which evolved in the Cretaceous. They are not very significant 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, art and culture.
Ferns are vascular plants differing from lycophytes by having leaves that are true. They differ from gymnosperms and angiosperms in lacking seeds and flowers but bear spores. Their life cycle shows alternation of production which means it is composed of diploid sporophytic and a haploid gametophytic phase. A spore grows by mitosis and creates gametophyte which develops photosynthetic prothallus. A mobile, flagellated sperm fertilizes the egg that’s attached to the prothallus. A zygote which is now diploid produces sporophyte by mitosis.
They prefer to stay in a huge variety of habitats ranging from distant mountain elevations, to arid 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, particularly when sheltered from the complete sun; acidity 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 supply of lipids, protein and carbs so are consumed by a few 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 known as fronds due to 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 in comparison 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 1 cell thick. It is heart of bladder shaped measuring 3-10 mm long and 2-8 mm broad. It produces gametes in the kind 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 construction that absorbs water and minerals. They anchor prothallus to soil.