Life Cycle of a FernFerns, unlike some other plants, do not flower in order to propagate. Instead, they reproduce sexually from spores. The life cycle of a fern is very different from the life cycle of many other plants. While many plants grow a mature adult form straight out of the seed, ferns have an intermediate stage, called a gametophyte, which then grows into a mature fern.

There are two distinct stages in the life cycle of ferns. The first stage is that of the gametophyte. Spores are produced on the underside of mature plants. These will germinate and grow into small, heart-shaped plants called gametophytes. The gametophytes produce both sperm and egg cells, and will fertilize itself, or others. Once the fertilization occurs, the adult fern will begin growing.

The second stage in the life cycle of a fern is the adult stage. The fertilized gametophytes begin to look like a mossy growth. After some time, young fronds will appear, rising out of the moss. If direct sunlight falls onto the young fronds for an extended period of time, the plant may die easily. This is because the tiny stems are not strong enough to sustain direct light and will dry out.

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Once these tiny fronds grow larger, the plant has a better chance of survival. When the veins are matured, moisture from the ground will be transported easily to the outermost leaves and the plant can withstand periods of direct sunlight. After the plant is large and mature, it will grow spores on the undersides of its leaves and the life cycle of a fern will begin again.A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta.[3] Unlikemosses, they have xylem and phloem (making them vascular plants). They have stems, leaves, and roots like other vascular plants. Ferns reproduce via spores and have neither seeds nor flowers.

By far the largest group of ferns is the leptosporangiate ferns, but ferns as defined here (also called monilophytes) include horsetails,whisk ferns, marattioid ferns, and ophioglossoid ferns. The term pteridophyte also refers to ferns and a few other seedless vascular plants (see classification section below).

Ferns first appear in the fossil record 360 million years ago in the Carboniferous but many of the current families and species did not appear until roughly 145 million years ago in the early Cretaceous (after flowering plants came to dominate many environments).

Ferns are not of major economic importance, but some are grown or gathered for food, as ornamental plants, for remediating contaminated soils, and have been the subject of research for their ability to remove some chemical pollutants from the air. Some are significant weeds. They also play a role in mythology, medicine, and art.Ferns are vascular plants differing from lycophytes by having true leaves (megaphylls), which are often pinnate. They differ from seed plants(gymnosperms and angiosperms) in their mode of reproduction-lacking flowers and seeds. Like all other vascular plants, they have a life cycle referred to as alternation of generations, characterized by alternating diploid sporophytic and haploid gametophytic phases. The diploid sporophyte has 2npaired chromosomes, where n varies from species to species. The haploid gametophyte has n unpaired chromosomes, i.e. half the number of the sporophyte. Unlike the gymnosperms and angiosperms, the ferns' gametophyte is a free-living organism.

Life cycle of a typical fern:

A diploid sporophyte phase produces haploid spores by meiosis (a process of cell division which reduces the number of chromosomes by a half).
A spore grows into a haploid gametophyte by mitosis (a process of cell division which maintains the number of chromosomes). The gametophyte typically consists of a photosynthetic prothallus.
The gametophyte produces gametes (often both sperm and eggs on the same prothallus) by mitosis.
A mobile, flagellate sperm fertilizes an egg that remains attached to the prothallus.
The fertilized egg is now a diploid zygote and grows by mitosis into a diploid sporophyte (the typical "fern" plant).The stereotypic image of ferns growing in moist shady woodland nooks is far from being a complete picture of the habitats where ferns can be found growing. Fern species live in a wide variety of habitats, from remote mountain elevations, to dry desert rock faces, to bodies of water or in open fields. Ferns in general may be thought of as largely being specialists in marginal habitats, often succeeding in places where various environmental factors limit the success of flowering plants. Some ferns are among the world's most serious weed species, including the bracken fern growing in the Scottish highlands, or the mosquito fern (Azolla) growing in tropical lakes, both species forming large aggressively spreading colonies. There are four particular types of habitats that ferns are found in: 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 (something like a quarter to a third of all fern species[4]).
Many ferns depend on associations with mycorrhizal fungi. Many ferns only grow within specific pH ranges; for instance, the climbing fern (Lygodium) of eastern North America will only grow in moist, intensely acid soils, while the bulblet bladder fern (Cystopteris bulbifera), with an overlapping range, is only found on limestone.
The spores are rich in lipids, protein and calories, so some vertebrates eat these. The European woodmouse (Apodemus sylvaticus) has been found to eat the spores of Culcita macrocarpa and the bullfinch (Pyrrhula murina) and the New Zealand lesser short-tailed bat (Mystacina tuberculata) also eat fern spores.Ferns first appear in the fossil record in the early-Carboniferous period. By the Triassic, the first evidence of ferns related to several modern families appeared. The "great fern radiation" occurred in the late-Cretaceous, when many modern families of ferns first appeared.
One problem with fern classification is the problem of cryptic species. A cryptic species is a species that is morphologically similar to another species, but differs genetically in ways that prevent fertile interbreeding. A good example of this is the currently designated species Asplenium trichomanes, the maidenhair spleenwort. This is actually a species complex that includes distinct diploid and tetraploid races. There are minor but unclear morphological differences between the two groups, which prefer distinctly differing habitats. In many cases such as this, the species complexes have been separated into separate species, thus raising the number of overall fern species. Possibly many more cryptic species are yet to be discovered and designated.
Ferns have traditionally been grouped in the Class Filices, but modern classifications assign them their own phylum or division in the plant kingdom, called Pteridophyta, also known as Filicophyta. The group is also referred to as Polypodiophyta, (or Polypodiopsida when treated as a subdivision of tracheophyta (vascular plants), although Polypodiopsida sometimes refers to only the leptosporangiate ferns). The term "pteridophyte" has traditionally been used to describe all seedless vascular plants, making it synonymous with "ferns and fern allies". This can be confusing since members of the fern phylum Pteridophyta are also sometimes referred to as pteridophytes.
Traditionally, three discrete groups of plants have been considered ferns: two groups of eusporangiate ferns-families Ophioglossaceae (adders-tongues, moonworts, and grape-ferns) and Marattiaceae-and the leptosporangiate ferns. The Marattiaceae are a primitive group of tropical ferns with a large, fleshy rhizome, and are now thought to be a sibling taxon to the main group of ferns, the leptosporangiate ferns. Several other groups of plants were considered "fern allies": the clubmosses, spikemosses, and quillworts in theLycopodiophyta, the whisk ferns in Psilotaceae, and the horsetails in the Equisetaceae. More recent genetic studies have shown that the Lycopodiophyta are more distantly related to other vascular plants, having radiated evolutionarily at the base of the vascular plant clade, while both the whisk ferns and horsetails are as much "true" ferns as are the Ophioglossoids and Marattiaceae. In fact, the whisk ferns and Ophioglossoids are demonstrably a clade, and the horsetails and Marattiaceae are arguably another clade. Molecular data-which remain poorly constrained for many parts of the plants' phylogeny - have been supplemented by recent morphological observations supporting the inclusion ofEquisetaceae within the ferns, notably relating to the construction of their sperm, and peculiarities of their roots.[2] However, there are still differences of opinion about the placement of the Equisetum species (see Equisetopsida for further discussion). One possible means of treating this situation is to consider only the leptosporangiate ferns as "true" ferns, while considering the other three groups as "fern allies". In practice, numerous classification schemes have been proposed for ferns and fern allies, and there has been little consensus among them.
A 2006 classification by Smith et al. is based on recent molecular systematic studies, in addition to morphological data. Their phylogeny is a consensus of a number of studies, and is shown below (to the level of orders).[2][6]Trachaeophyta
lycophytes (club mosses, spike mosses, quillworts)
euphyllophytes
spermatophytes (seed plants)
fernsPsilotopsida
Psilotales (whisk ferns)
Ophioglossales (grapeferns etc.)
Equisetopsida
Equisetales (horsetails)
Marattiopsida
Marattiales
Polypodiopsida
Osmundales
Hymenophyllales (filmy ferns)
Gleicheniales
Schizaeales
Salviniales (heterosporous)
Cyatheales (tree ferns)
Polypodiales
eusporangiate
ferns
leptosporangiate
ferns

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