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| | [[Image:Seedling_cotyledons_small.jpg|thumb|right|This [[seedling]] germinated producing two plain-looking cotyledons later followed by two normal-looking leaves that are small copies of the adult leaves.]] | | [[Image:Seedling_cotyledons_small.jpg|thumb|right|This [[seedling]] germinated producing two plain-looking cotyledons later followed by two normal-looking leaves that are small copies of the adult leaves.]] |
| − | [[Image:Cotyledon-Cercis_siliquastrum.jpg|thumb|right|cotyledon in formation before the accumulation of the reserves seen at Judas-tree (''Cercis siliquastrum'')]] | + | [[Seed]]-[[leaf]]; the primary leaf or leaves in the embryo; in some plants the cotyledon always remains in the seed-coats and in others (as [[bean]]) it emerges on [[germination]]. |
| − | [[Image:Monocot_vs_dicot_crop_Pengo.jpg|thumb|Comparison of a monocot and dicot sprouting]] | |
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| − | A '''cotyledon''' ([[Greek language|Greek]]: ''κοτυληδών'') is a significant part of the [[embryo]] within the [[seed]] of a [[plant]]. Upon [[germination]], the cotyledon usually becomes 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.
| + | ==Gallery== |
| | + | <gallery> |
| | + | Image:Cotyledon-Cercis_siliquastrum.jpg|cotyledon in formation before the accumulation of the reserves seen at Judas-tree (''Cercis siliquastrum'') |
| | + | Image:Monocot_vs_dicot_crop_Pengo.jpg|Comparison of a monocot and dicot sprouting |
| | + | Image:Seekiefer (Pinus pinaster) 14d 1.jpg|A seedling of [[Maritime Pine]] with eight cotyledons |
| | + | </gallery> |
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| − | The cotyledon of [[Poaceae|grasses]] and many other monocotyledons is highly modified and composed of a ''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).
| + | {{glossary}} |
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| − | [[Image:Seekiefer (Pinus pinaster) 14d 1.jpg|left|thumb|A seedling of [[Maritime Pine]] with eight cotyledons]]
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| − | [[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).
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| − | 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.
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| − | 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. <br clear = left>
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| − | ==References==
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| − | *Mirov, N. T. (1967). ''The Genus Pinus''. Ronald Press Company, New York.
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| − | *Farjon, A. & Styles, B. T. (1997). Pinus (Pinaceae). ''Flora Neotropica Monograph'' 75: 221-224.
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| − | [[Category:Botany]]
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