Cotyledon 55623 222523466 2008-06-29T20:20:08Z 212.251.121.97 {{expand|date=July 2007}} {{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]]