Cotyledon
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2008-06-29T20:20:08Z
212.251.121.97
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{{otheruses}}
[[Image:Cotyledon-Cercis_siliquastrum.jpg|thumb|right|Cotyledon in formation before the accumulation of the reserve seen at [[Judas-tree]] (''Cercis siliquastrum'')]]
[[Image:Monocot_vs_dicot_crop_Pengo.jpg|thumb|Comparison of a monocot and dicot sprouting]]
A '''cotyledon''' (or "seed leaf") ([[Greek language|Greek]]: κοτυληδών, ''kotylēdōn'', from κοτύλη, [[Cotyla|''kotýlē'']], a [[cup]] or [[bowl]]) is a significant part of the [[embryo]] within the [[seed]] of a [[plant]]. Upon [[germination]], the cotyledon may become the embryonic first [[leaf|leaves]] of a seedling. The number of cotyledons present is one characteristic used by botanists to classify the [[flowering plant]]s (angiosperms). Species with one cotyledon are called [[monocotyledonous]] (or, "monocots") and placed in the Class Liliopsida. Plants with two embryonic leaves are termed [[dicotyledonous]] ("dicots") and placed in the Class Magnoliopsida(Jackson, 08).
The cotyledon of [[Poaceae|grasses]] and many other monocotyledons is 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, and these are often variable in number (multicotyledonous), with from 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]] (''Pinus radiata'') seedlings have 5–9, and [[Jeffrey Pine]] (''Pinus jeffreyi'') 7–13 (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).
<br>[[Image:Seekiefer (Pinus pinaster) 14d 1.jpg|left|thumb|150px|A seedling of [[Maritime Pine]] with eight cotyledons]]
The cotyledons may be ephemeral, lasting only days after emergence, or persistent, enduring a year or more 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.
Cotyledons may be either [[epigeal]], expanding on the germination of the seed, throwing off the seed shell and become photosynthetic above the ground; or [[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.
==References==
*[[http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0006930.html Tiscali.reference - Cotyledon]]
*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.
[[Category:Plant anatomy]]
[[Category:Plant morphology]]
[[Category:Plant reproduction]]
[[ca:Cotiledó]]
[[cs:Děložní lístek]]
[[da:Kimblad]]
[[de:Kotyledon]]
[[es:Cotiledón]]
[[eo:Kotiledono]]
[[fr:Cotylédon]]
[[gl:Cotiledón]]
[[hr:Supka]]
[[is:Fræblað]]
[[it:Cotiledone]]
[[ka:ლებანი]]
[[ms:Kotiledon]]
[[nl:Zaadlob]]
[[pl:Liścień]]
[[pt:Cotilédone]]
[[fi:Sirkkalehti]]
[[sv:Hjärtblad]]
[[zh:子叶]]