Editing Fern (section)

==Description==

=== Sporophyte ===

Extant ferns are herbaceous [[Perennial plant|perennials]] and most lack [[wood]]y growth.<ref>{{Cite book |last=Mauseth |first=James D. |url=https://books.google.com/books?id=UEsBPPlxP7EC&pg=PA492 |title=Botany: an Introduction to Plant Biology |date=September 2008 |publisher=Jones & Bartlett Publishers |isbn=978-1-4496-4720-9 |page=492}}</ref> When woody growth is present, it is found in the stem.<ref name="Levyns-1966">{{Cite book |last=Levyns |first=M. R. |title=A Guide to the Flora of the Cape Peninsula |publisher=Juta & Company |year=1966 |edition=2nd Revised |oclc=621340}}</ref> Their foliage may be [[deciduous]] or [[evergreen]],<ref>{{Cite book |last1=Fernández |first1=Helena |url=https://books.google.com/books?id=smtpBM7UgXEC&pg=PA175 |title=Working with Ferns: Issues and Applications |last2=Kumar |first2=Ashwani |last3=Revilla |first3=Maria Angeles |date=2010-11-11 |publisher=Springer |isbn=978-1-4419-7162-3 |page=175}}</ref> and some are semi-evergreen depending on the climate.<ref>{{Cite book |last=Hodgson |first=Larry |url=https://books.google.com/books?id=HDij6Fmk2MwC&pg=PA329 |title=Making the Most of Shade: How to Plan, Plant, and Grow a Fabulous Garden that Lightens Up the Shadows |date=2005-01-01 |publisher=Rodale |isbn=978-1-57954-966-4 |page=329}}</ref> Like the sporophytes of seed plants, those of ferns consist of stems, leaves and roots. Ferns differ from [[spermatophyte]]s in that they reproduce by spores rather than having flowers and producing seeds.<ref name="Levyns-1966" /> However, they also differ from spore-producing [[bryophyte]]s in that, like seed plants, they are [[polysporangiophyte]]s, their [[sporophyte]]s branching and producing many sporangia. Also unlike bryophytes, fern sporophytes are free-living and only briefly dependent on the maternal [[gametophyte]].

The [[green]], [[photosynthesis|photosynthetic]] part of the plant is technically a [[microphyll#evolution of leaves: microphyll and megaphyll|megaphyll]] and in ferns, it is often called a ''[[frond]]''. New leaves typically expand by the unrolling of a tight spiral called a crozier or [[fiddlehead fern|fiddlehead]] into [[frond]]s.{{sfn|McCausland|2019}} This uncurling of the leaf is termed [[circinate vernation]]. Leaves are divided into two types: sporophylls and tropophylls. [[Sporophyll]]s produce spores; [[tropophyll]]s do not. Fern spores are borne in [[sporangia]] which are usually clustered to form [[sorus|sori]]. The sporangia may be covered with a protective coating called an [[indusium]]. The arrangement of the sporangia is important in classification.<ref name="Levyns-1966" />

In monomorphic ferns, the fertile and sterile leaves look morphologically the same, and both are able to photosynthesize. In hemidimorphic ferns, just a portion of the fertile leaf is different from the sterile leaves. In dimorphic (holomorphic) ferns, the two types of leaves are [[frond dimorphism|morphologically distinct]].<ref>[https://2019.botanyconference.org/engine/search/index.php?func=detail&aid=758 Understanding the contribution of LFY and PEBP flowering genes to fern leaf dimorphism – Botany 2019].</ref> The fertile leaves are much narrower than the sterile leaves, and may have no green tissue at all, as in the [[Blechnaceae]] and [[Lomariopsidaceae]].

[[File:Croziers, fronds, rhizomes of bracken fern.jpg|thumb|Croziers, fronds, and [[rhizome]]s of bracken. In this species the stems grow underground, allowing the plant to spread horizontally.]]

The anatomy of fern leaves can be anywhere from simple to highly divided, or even [[Indeterminate growth|indeterminate]] (e.g. [[Gleicheniaceae]], [[Lygodium|Lygodiaceae]]). The divided forms are [[Pinnation|pinnate]], where the leaf segments are completely separated from one other, or pinnatifid (partially pinnate), where the leaf segments are still partially connected. When the fronds are branched more than once, it can also be a combination of the pinnatifid are pinnate shapes. If the leaf blades are divided twice, the plant has bipinnate fronds, and tripinnate fronds if they branch three times, and all the way to tetra- and pentapinnate fronds.<ref>[https://www.fs.fed.us/wildflowers/beauty/ferns/structure.shtml Fern Structure – Forest Service].</ref><ref>[https://www.nzplants.auckland.ac.nz/en/about/ferns/structure/frond.html Fern Structure – Forest Service], Auckland, New Zealand.</ref> In tree ferns, the main stalk that connects the leaf to the stem (known as the stipe), often has multiple leaflets. The leafy structures that grow from the stipe are known as pinnae and are often again divided into smaller pinnules.<ref>{{cite web |url=http://www.basicbiology.net/plants/ferns/fronds.php |title=Fern Fronds |publisher=Basic Biology |access-date=2014-12-06 |archive-date=19 April 2015 |archive-url=https://web.archive.org/web/20150419003216/http://basicbiology.net/plants/ferns/fronds.php |url-status=dead}}</ref>

Fern stems are often loosely called [[rhizome]]s, even though they grow underground only in some of the species. Epiphytic species and many of the terrestrial ones have above-ground creeping [[stolon]]s (e.g., [[Polypodiaceae]]), and many groups have above-ground erect semi-woody trunks (e.g., [[Cyatheaceae]], the scaly tree ferns). These can reach up to {{convert|20|m|ft|sp=us}} tall in a few species (e.g., ''[[Cyathea brownii]]'' on [[Norfolk Island]] and ''[[Cyathea medullaris]]'' in [[New Zealand]]).<ref>{{cite book |first1=Mark F. |last1=Large |first2=John E. |last2=Braggins |author-link2=John E. Braggins |date=2004 |title=Tree Ferns |publisher=Timber Press |isbn=0881926302 |url-access=registration |url=https://archive.org/details/treeferns00mark |page= }}</ref>

Roots are underground non-photosynthetic structures that take up water and nutrients from [[soil]]. They are always [[fibrous root system|fibrous]] and are structurally very similar to the roots of seed plants.

=== Gametophyte ===

As in all [[vascular plant]]s, the sporophyte is the dominant phase or [[alternation of generations|generation in the life cycle]]. The [[gametophyte]]s of ferns, however, are very different from those of seed plants. They are free-living and resemble [[liverworts]], whereas those of seed plants develop within the spore wall and are dependent on the parent sporophyte for their nutrition. A fern gametophyte typically consists of:<ref name=":0" />

* [[Prothallus]]: A green, photosynthetic structure that is one cell thick, usually heart or kidney shaped, 3–10 mm long and 2–8 mm broad. The prothallus produces gametes by means of:
** [[Antheridium|Antheridia]]: Small spherical structures that produce [[flagellum|flagellate]] antherozoids.<ref name=":0" />
** [[Archegonium|Archegonia]]: A flask-shaped structure that produces a single egg at the bottom, reached by the male gametophyte by swimming down the neck.<ref name=":0" />
* [[Rhizoid]]s: [[root]]-like structures (not true roots) that consist of single greatly elongated cells, that absorb water and mineral [[salts]] over the whole structure. Rhizoids anchor the prothallus to the soil.<ref name=":0" />