Editing Fern (section)

== Ecology ==

Fern species live in a wide variety of [[habitat]]s, from remote [[mountain]] elevations, to dry [[desert]] rock faces, bodies of water or 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 plant]]s. 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 [[forest]]s; crevices in rock faces, especially when sheltered from the full sun; acid wetlands including [[bog]]s and [[swamp]]s; and tropical [[tree]]s, where many species are [[epiphyte]]s (something like a quarter to a third of all fern species).{{sfn|Schuettpelz|2007|loc=Part I}}

Especially the epiphytic ferns have turned out to be hosts of a huge diversity of invertebrates. It is assumed that [[bird's-nest fern]]s alone contain up to half the invertebrate biomass within a hectare of [[rainforest]] canopy.<ref>{{Cite web|url=https://www.science.org/content/article/ferns-brimming-life|title=Ferns Brimming With Life|date=2 June 2004|website=Science &#124; AAAS}}</ref>

Many ferns depend on associations with [[mycorrhizal]] fungi. Many ferns grow only within specific pH ranges; for instance, the climbing fern (''[[Lygodium palmatum]]'') of eastern [[North America]] will grow only in moist, intensely [[acid]] soils, while the bulblet bladder fern (''[[Cystopteris bulbifera]]''), with an overlapping range, is found only on [[limestone]].

The spores are rich in [[lipid]]s, [[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.<ref>{{cite news|url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8523000/8523825.stm|title=A mouse that eats ferns like a dinosaur|last=Walker|first=Matt|date=19 February 2010|publisher=BBC Earth News|access-date=2010-02-20}}</ref>

<gallery class=center mode=nolines widths=300 heights=250>
File:CowellFerns.JPG|In undergrowth below [[Sequoia sempervirens|coast redwoods]], California
File:FernBedInForest.jpg|Fern bed under a forest canopy, Virginia
File:Samambaia fern.jpg|On a wall
File:Harts Tongue Fern on the Great Orme - geograph.org.uk - 345785.jpg|''[[Asplenium]]'' hart's tongue fern in a [[wikt:gryke|gryke]] in [[limestone pavement]]
File:... epiphytic fern (49095803342).jpg|[[Epiphyte|Epiphytic]] ferns in India
File:Canning_rv_azolla_10_gnangarra.jpg|''[[Azolla]]'' duckweed fern covering<br/>the [[Canning River]], Western Australia
</gallery>

=== Life cycle ===

Ferns are [[vascular plant]]s differing from [[lycophyte]]s by having true [[leaf|leaves]] (megaphylls), which are often [[pinnate]]. They differ from [[spermatophyte|seed plant]]s ([[gymnosperm]]s and [[angiosperm]]s) in reproducing by means of spores and lacking [[flower]]s and [[seed]]s. Like all [[embryophyte|land plants]], they have a [[biological life cycle|life cycle]] referred to as [[alternation of generations]], characterized by alternating [[diploid]] [[sporophyte|sporophytic]] and [[haploid]] [[gametophyte|gametophytic]] phases. The diploid sporophyte has 2''n'' paired [[chromosome]]s, where ''n'' varies from species to species. The haploid gametophyte has ''n'' unpaired chromosomes, i.e. half the number of the sporophyte. The gametophyte of ferns is a free-living organism, whereas the gametophyte of the gymnosperms and angiosperms is dependent on the sporophyte.

The life cycle of a typical fern proceeds as follows:
# A diploid sporophyte phase produces haploid [[spore]]s by [[meiosis]] (a process of cell division which reduces the number of chromosomes by a half).
# A spore grows into a free-living 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 [[Ovum|egg]]s on the same prothallus) by mitosis.
# A mobile, [[flagellum|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).

Sometimes a gametophyte can give rise to sporophyte traits like roots or sporangia without the rest of the sporophyte.<ref>[https://books.google.com/books?id=x494WF2PvbsC&pg=PA324 The Ferns (Filicales): Volume 1, Analytical Examination of the Criteria of Comparison: Treated Comparatively with a View to their Natural Classification]</ref>

<gallery class=center mode=nolines widths=300 heights=250>
File:Monarch fern sori.jpeg|[[Sorus]] of [[monarch fern]], with [[sporangium]]
File:Onoclea sensibilis 3 crop.JPG|Gametophyte ([[thallus]]) and sporophyte (ascendant frond) of ''[[Onoclea sensibilis]]''
</gallery>