Editing Cotyledon

{{Short description|Embryonic leaf first appearing from a germinating seed}}
{{Other uses}}
{{distinguish|Cotyledion|cotylenol}}
[[File:Cotyledon-Cercis siliquastrum.jpg|thumb|Cotyledon from a [[Judas-tree]] (''Cercis siliquastrum'', a dicot) seedling]]
[[File:Monocot vs dicot crop Pengo.jpg|thumb|Comparison of a monocot and dicot sprouting. The visible part of the monocot plant (left) is actually the first true leaf produced from the [[meristem]]; the cotyledon itself remains within the seed.]]

A '''cotyledon''' ({{IPAc-en|ˌ|k|ɒ|t|ᵻ|ˈ|l|iː|d|ən}} {{respell|KOT|ill|EE| dən}}; {{etymology|la|{{wikt-lang|la|cotyledon}}}};{{sfn|Short|George|2013|loc=[https://books.google.com/books?id=dFcKLxqEAj4C&pg=PA15]|page=15}} {{etymology||''{{wikt-lang|grc|κοτυληδών}}'' ({{grc-transl|κοτυληδών}})}} "a cavity, small cup, any cup-shaped hollow",<ref>{{Cite book |last=Quattrocchi |first=Umberto |url=https://books.google.com/books?id=esMPU5DHEGgC |title=CRC World Dictionary of Plant Names: Common Names, Scientific Names, Eponyms, Synonyms, and Etymology |date=17 November 1999 |publisher=CRC Press |isbn=9780849326752 |volume=1 |publication-place=Boca Raton, Florida |page=628 |quote=Greek ''kotyle'', ''kotyledon'' 'a cavity, small cup, any cup-shaped hollow,' in allusion to the receptacle or to the space at the base of the leaves [...]. |access-date=12 May 2024}}</ref>
gen. {{wikt-lang|grc|κοτυληδόνος}} ({{grc-transl|κοτυληδόνος}}), {{etymology||''{{wikt-lang|grc|κοτύλη}}'' ([[cotyla|kotýlē]])|cup, bowl}}) is a "seed leaf" – a significant part of the [[embryo]] within the [[seed]] of a [[plant]] – and is formally defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a [[germination|germinating]] seed."{{sfn|OED}} Botanists use the number of cotyledons present as one characteristic to classify the [[flowering plant]]s (angiosperms): species with one cotyledon are called [[monocotyledonous]] ("monocots"); plants with two embryonic leaves are termed [[dicotyledonous]] ("dicots"). Be it noted that many [[orchids]] with minute seeds have no identifiable cotyledon, and are regarded as [[acotyledons]]. The Dodders ([[Cuscuta]] spp) also lack cotyledons, as does the African tree [[Mammea africana]] ([[Calophyllaceae]]).<ref>{{Cite journal |last1=Yamoto |first1=Takakazu |last2=Maruhashi |first2=Tamaki |date=December 1995 |title=Seed Dispersal by Elephants...etc |journal=Biotropica |volume=27 |issue=4 |page=528}}</ref>

In the case of dicot seedlings whose cotyledons are photosynthetic, the cotyledons are functionally similar to leaves. However, true leaves and cotyledons are developmentally distinct. Cotyledons form during [[embryogenesis]], along with the root and shoot [[meristem]]s, and are therefore present in the seed prior to germination. True leaves, however,  form post-embryonically (i.e. after germination) from the shoot apical meristem, which generates subsequent aerial portions of the plant.

The cotyledon of [[Poaceae|grasses]] and many other monocotyledons is a highly modified leaf composed of a  [[Scutellum (botany)|''scutellum'']] and a ''[[coleoptile]]''. The scutellum is a tissue within the seed that is specialized to absorb stored food from the adjacent [[endosperm]]. The coleoptile is a protective cap that covers the ''plumule'' (precursor to the stem and leaves of the plant).

[[Gymnosperm]] seedlings also have cotyledons. [[Gnetophyta|Gnetophytes]], [[cycad]]s, and [[Ginkgophyta|ginkgos]] all have 2, whereas in conifers they are often variable in number (multicotyledonous), with 2 to 24 cotyledons forming a whorl at the top of the [[hypocotyl]] (the embryonic stem) surrounding the plumule. Within each species, there is often still some variation in cotyledon numbers, e.g. [[Monterey Pine|Monterey pine]] (''Pinus radiata'') seedlings have between 5 and 9, and [[Jeffrey Pine|Jeffrey pine]] (''Pinus jeffreyi'') 7 to 13 (Mirov 1967), but other species are more fixed, with e.g. [[Cupressus sempervirens|Mediterranean cypress]] always having just two cotyledons. The highest number reported is for [[big-cone pinyon]] (''Pinus maximartinezii''), with 24 (Farjon & Styles 1997).

Cotyledons may be ephemeral, lasting only days after emergence, or persistent, enduring at least a year on the plant. The cotyledons contain (or in the case of gymnosperms and monocotyledons, have access to) the stored food reserves of the seed. As these reserves are used up, the cotyledons may turn green and begin [[photosynthesis]], or may wither as the first true leaves take over food production for the seedling.<ref name="Vines 1913" />

==Epigeal versus hypogeal development==
{{Main|Epigeal germination|Hypogeal germination}}
[[File:Germination-en.svg|thumb|335px|Schematic of epigeal vs hypogeal germination]]

[[File:Peanut cotyledons.jpg|thumb|left|[[Peanut]] seeds split in half, showing the embryos with cotyledons and primordial root]]
[[File:09-05-31 Abeto Douglas.jpg|thumb|left|Two-week-old [[Douglas fir]] (a conifer) with seven cotyledons]]
[[File:Mimosa pudica - cotyledon.jpg|thumb|''Mimosa pudica'' (a dicot) seedling with two cotyledons and the first "true" leaf with six leaflets]]
Cotyledons may be either [[epigeal germination|epigeal]], expanding on the germination of the seed, throwing off the seed shell, rising above the ground, and perhaps becoming photosynthetic; or [[hypogeal germination|hypogeal]], not expanding, remaining below ground and not becoming photosynthetic. The latter is typically the case where the cotyledons act as a storage organ, as in many [[nut (fruit)|nuts]] and [[acorn]]s.{{cn|date=February 2023}}

Hypogeal plants have (on average) significantly larger seeds than epigeal ones. They are also capable of surviving if the seedling is clipped off, as [[meristem]] buds remain underground (with epigeal plants, the meristem is clipped off if the seedling is grazed). The tradeoff is whether the plant should produce a large number of small seeds, or a smaller number of seeds which are more likely to survive.<ref name="tischler">{{Cite conference |last1=Charles R. Tischler |last2=Justin D. Derner |last3=H. Wayne Polley |last4=Hyrum B. Johnson |year=2007 |title=Response of Seedlings of Two Hypogeal Brush Species to CO2 Enrichment |url=http://www.treesearch.fs.fed.us/pubs/28366 |conference=Proceedings: Shrubland dynamics -- fire and water; 2004 August 10–12; Lubbock, TX. Proceedings RMRS-P-47 |publisher=Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station |volume=047 |pages=104–106 |journal=In: Sosebee, Ronald E.; Wester, David B.; Britton, Carlton M.; Mcarthur, E. Durant; Kitchen, Stanley G., Comps. Proceedings: Shrubland Dynamics -- Fire and Water; 2004 August 10–12; Lubbock, Tx. Proceedings RMRS-P-47. Fort Collins, Co: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. P. 104-106.}}</ref><ref>{{Citation |last1=Baraloto, C. |title=Seed size, seedling morphology, and response to deep shade and damage in neotropical rain forest trees |journal=American Journal of Botany |volume=94 |issue=6 |pages=901–11 |year=2007 |doi=10.3732/ajb.94.6.901 |pmid=21636459 |s2cid=24272337 |last2=Forget |first2=P.-M.|bibcode=2007AmJB...94..901B }}</ref>

The ultimate development of the epigeal habit is represented by a few plants, mostly in the family [[Gesneriaceae]] in which the cotyledon persists for a lifetime. Such a plant is [[Streptocarpus|''Streptocarpus wendlandii'']] of [[South Africa]] in which one cotyledon grows to be up to 75 centimeters (2.5 feet) in length and up to 61&nbsp;cm (two feet) in width (the largest cotyledon of any dicot,<ref name="Nishii-et-al-2004">{{Cite journal |last1=Nishii |first1=Kanae |last2=Kuwabara |first2=Asuka |last3=Nagata |first3=Toshiyuki |date=2004 |title=Characterization of Anisocotylous Leaf Formation in Streptocarpus Wendlandii (Gesneriaceae): Significance of Plant Growth Regulators. |journal=Annals of Botany |volume=94 |issue=3 |pages=457–67 |doi=10.1093/aob/mch160 |jstor=42759229 |pmc=4242185 |pmid=15286012}}</ref> and exceeded only by ''Lodoicea''). Adventitious flower clusters form along the midrib of the cotyledon.<ref>{{Cite book |last=Perry |first=Frances and Leslie Greenwood |title=Flowers of the World |date=1972 |publisher=Hamlyn Publishing Group |location=London |page=47}}</ref> The second cotyledon is much smaller and ephemeral.{{Cn|date=May 2023}}

Related plants may show a mixture of hypogeal and epigeal development, even within the same plant family. Groups which contain both hypogeal and epigeal species include, for example, the Southern Hemisphere conifer family [[Araucariaceae]],<ref>{{Citation |last1=Hiroaki Setoguchi |title=Phyloghuhenetic relationships within Araucariaceae based on rbcL gene sequences |journal=American Journal of Botany |volume=85 |issue=11 |pages=1507–1516 |year=1998 |doi=10.2307/2446478 |jstor=2446478 |pmid=21680310 |last2=Takeshi Asakawa Osawa |last3=Jean-Christophe Pintaud |last4=Tanguy Jaffré |last5=Jean-Marie Veillon}}</ref> the pea family, [[Fabaceae]],<ref name="tischler" /> and the genus ''[[Lilium]]'' (see [[Lily seed germination types]]).  The frequently garden grown [[common bean]], ''Phaseolus vulgaris'', is epigeal, while the closely related [[runner bean]], ''Phaseolus coccineus'', is hypogeal.{{Cn|date=May 2023}}

==History==
The term ''cotyledon'' was coined by [[Marcello Malpighi]] (1628–1694).{{efn|The Oxford English Dictionary attributes it [[Carl Linnaeus|Linnaeus]] (1707–1778) "1751 Linnaeus ''Philos. Bot.'' 54. ''Cotyledon, corpus laterale seminis, bibulum, caducum''"{{sfn|Linnaeus|1751|loc=[https://archive.org/stream/philosophiabotan00linn#page/54/mode/2up p.&nbsp;54]}} and 89,{{sfn|Linnaeus|1751|loc=[https://archive.org/stream/philosophiabotan00linn#page/89/mode/1up p.&nbsp;89]}} by analogy with a similar structure of the same name in the [[Cotyledon (placenta)|placenta]].{{sfn|OED}}}} [[John Ray]] was the first botanist to recognize that some plants have two and others only one, and eventually the first to recognize the immense importance of this fact to [[systematics]], in ''Methodus plantarum'' (1682).<ref name="Vines 1913">{{Citation |last=Vines, Sydney Howard |title=Makers of British botany |pages=8–43 |year=1913 |editor-last=Oliver, Francis Wall |editor-link=Francis Wall Oliver |chapter=Robert Morison 1620—1683 and John Ray 1627—1705 |publisher=Cambridge University Press |author-link=Sydney Howard Vines}}</ref><ref name="Greene 1983">{{Cite book |last=Greene |first=Edward Lee |author-link=Edward Lee Greene |url=https://books.google.com/books?id=AzGsAAAAIAAJ&pg=PA1019 |title=Landmarks of botanical history: Part 2 |date=1983 |publisher=Stanford University Press |isbn=978-0-8047-1075-6 |editor-last=Egerton |editor-first=Frank N. |location=Stanford, California |page=1019, note 15}}</ref>

[[Theophrastus]] (3rd or 4th century BC) and [[Albertus Magnus]] (13th century) may also have recognized the distinction between the dicotyledons and monocotyledons.<ref>{{Cite web |title=Bioetymology: Origin in Biomedical Terms: cotyledon, monocotyledon (plural usually monocots), dicotyledons(plural usually dicot) |url=http://bioetymology.blogspot.com.br/2011/06/cotyledon-monocotyledon-plural-usually.html |access-date=6 April 2018 |website=bioetymology.blogspot.com.br}}</ref><ref name="Greene 1983" />

== Notes ==
{{notelist}}

==References==
{{Reflist|30em}}

==Bibliography==
{{refbegin|30em}}
* {{Cite book |last=Linnaeus |first=Carl |author-link=Carl Linnaeus |url=https://archive.org/details/philosophiabotan00linn |title=Philosophia botanica : in qua explicantur fundamenta botanica cum definitionibus partium, exemplis terminorum, observationibus rariorum, adiectis figuris aeneis |date=1755 |publisher=Joannis Thomae Trattner |others=originally published simultaneously by R. Kiesewetter (Stockholm) and Z. Chatelain (Amsterdam) |location=Vienna |ref={{harvid|Linnaeus|1751}} |access-date=13 December 2015 |orig-year=1751}}
* Mirov, N. T. (1967). ''The Genus Pinus''. Ronald Press Company, New York.
* Farjon, A. & Styles, B. T. (1997). Pinus (Pinaceae). ''Flora Neotropica Monograph'' 75: 221–224.
* {{Cite OED |Cotyledon|ref={{harvid|OED}}}}
* {{Cite book |last1=Short |first1=Emma |url=https://books.google.com/books?id=dFcKLxqEAj4C |title=A primer of botanical Latin with vocabulary |last2=George |first2=Alex |date=2013 |publisher=Cambridge University Press |isbn=9781107693753 |location=New York |access-date=14 December 2015}}
{{refend}}

==External links==
* [https://web.archive.org/web/20020607050508/http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0006930.html Tiscali.reference – Cotyledon]

{{Commons category|Cotyledons (leaves)|Cotyledon}}
{{wiktionary}}

[[Category:Plant anatomy]]
[[Category:Plant morphology]]
[[Category:Plant reproduction]]
[[Category:Leaves]]