Difference between revisions of "Ginkgo"

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{{About|the genus of mainly extinct trees|its single extant species, the ginkgo tree|Ginkgo biloba}}
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#redirect [[:Category:Ginkgo]]
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{{Automatic taxobox
 
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| fossil_range = {{fossil range|270|0}}[[Permian]]<ref>[[#Taylor|Taylor & Taylor (1993)]], pp. 138, 197.</ref> to [[Holocene|Present]]
 
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| image = Ginkgo biloba MacAbee BC.jpg
 
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| image_caption = ''Ginkgo biloba'' [[Eocene]], McAbee, [[British Columbia|B.C.]], Canada
 
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| authority = [[Carl Linnaeus|L.]]&nbsp;<ref>{{cite web |url=http://apps.kew.org/wcsp/namedetail.do?name_id=334052 |title=''Ginkgo'' L., Mant. Pl. 2: 313 (1771) |work=[[World Checklist of Selected Plant Families]] |publisher=[[Royal Botanic Gardens, Kew]] |accessdate=June 8, 2013 |author=R. Govaerts}}</ref>
 
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| subdivision_ranks = Species
 
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| subdivision =
 
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*†''[[Ginkgo adiantoides]]''
 
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*†''[[Ginkgo apodes]]''
 
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*''[[Ginkgo biloba]]''
 
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*†''[[Ginkgo cranei]]''
 
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*†''[[Ginkgo digitata]]''
 
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*†''[[Ginkgo dissecta]]''
 
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*†''[[Ginkgo gardneri]]''
 
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*†''[[Ginkgo ginkgoidea]]''
 
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*†''[[Ginkgo huolinhensis]]''
 
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*†''[[Ginkgo huttonii]]''
 
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*†''[[Ginkgo yimaensis]]''
 
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| synonyms=''Salisburia'' <small>[[James Edward Smith|Sm.]]</small>
 
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| synonyms_ref = &nbsp;<ref name=GRIN>{{cite web |url=http://www.ars-grin.gov/cgi-bin/npgs/html/genus.pl?4960 | title=Genus: ''Ginkgo'' L. |accessdate=June 8, 2013 | work=[[Germplasm Resources Information Network]] |publisher=[[United States Department of Agriculture]]}}</ref>
 
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'''''Ginkgo''''' is a [[genus]] of highly unusual non-flowering plants. The scientific name is also used as the English name. The order to which it belongs, [[Ginkgoales]], first appeared in the [[Permian]],<ref>Royer et al (2003)</ref> 270 million years ago, possibly derived from "[[seed fern]]s" of the order [[Peltaspermales]]. The rate of evolution within the genus has been slow, and almost all its species had become extinct by the end of the [[Pliocene]]; the exception is the sole living species, ''[[Ginkgo biloba]]'', which is only found in the wild in China, but is cultivated across the world. The relationships between ginkgos and other groups of plants are not fully resolved.
 
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== Prehistory ==
 
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The ginkgo (Ginkgoales) is a [[living fossil]], with fossils recognisably related to modern ginkgo from the [[Permian]], dating back 270&nbsp;million years. The most plausible ancestral group for the order Ginkgoales is the Pteridospermatophyta, also known as the "[[seed fern]]s", specifically the order [[Peltaspermales]]. The closest living relatives of the clade are the [[cycad]]s,<ref>[[#Royer|Royer ''et al''. (2003)]], p.&nbsp;84.</ref> which share with the extant ''G.&nbsp;biloba'' the characteristic of motile sperm.  Fossils attributable to the genus ''Ginkgo'' first appeared in the [[Early Jurassic]], and the genus diversified and spread throughout [[Laurasia]] during the middle [[Jurassic]] and [[Early Cretaceous]]. It declined in diversity as the Cretaceous progressed with the extinction of species such as ''[[Ginkgo huolinhensis]]'', and by the [[Paleocene|Palaeocene]], only a few ''Ginkgo'' species, ''[[Ginkgo cranei]]'' and ''[[Ginkgo adiantoides]]'', remained in the Northern Hemisphere, while a markedly different (and poorly documented) form persisted in the [[Southern Hemisphere]].{{Citation needed|date=June 2013}}  At the end of the [[Pliocene]], ''Ginkgo'' fossils disappeared from the fossil record everywhere except in a small area of central China, where the modern species survived. It is doubtful whether the Northern Hemisphere fossil species of ''Ginkgo'' can be reliably distinguished. Given the slow pace of evolution and morphological similarity between members of the genus, there may have been only one or two species existing in the Northern Hemisphere through the entirety of the [[Cenozoic]]: present-day ''G.&nbsp;biloba'' (including ''G.&nbsp;adiantoides'') and ''[[Ginkgo gardneri|G.&nbsp;gardneri]]'' from the Palaeocene of [[Scotland]].<ref>[[#Royer|Royer ''et al''. (2003)]], p.&nbsp;85.</ref>
 
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[[File:Fossil Plant Ginkgo.jpg|left|thumb|Fossil ''[[Ginkgo huttonii]]'' leaves from the Jurassic of England]]
 
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At least morphologically, ''G.&nbsp;gardneri'' and the Southern Hemisphere species are the only known post-Jurassic taxa that can be unequivocally recognised. The remainder may have been [[ecotype]]s or [[subspecies]]. The implications would be that ''G.&nbsp;biloba'' had occurred over an extremely wide range, had remarkable genetic flexibility and, though [[evolution|evolving]] genetically, never showed much [[speciation]]. While it may seem improbable that a species may exist as a contiguous entity for many millions of years, many of the ginkgo's life-history parameters fit. These are: extreme longevity; slow reproduction rate; (in Cenozoic and later times) a wide, apparently contiguous, but steadily contracting distribution coupled with, as far as can be demonstrated from the fossil record, extreme ecological conservatism (restriction to disturbed streamside environments).<ref name="Royer_91">[[#Royer|Royer ''et al''. (2003)]], p.&nbsp;91.</ref>
 
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Modern-day ''G.&nbsp;biloba'' grows best in well-watered and drained environments,<ref>[[#Royer|Royer ''et al''. (2003)]], p.&nbsp;87.</ref> and the extremely similar fossil ''Ginkgo'' favoured similar environments; the sediment records at the majority of fossil ''Ginkgo'' localities indicate it grew primarily in disturbed environments along streams and levees.<ref name="Royer_91"/> ''Ginkgo'' therefore presents an "ecological paradox" because, while it possesses some favourable traits for living in disturbed environments (clonal reproduction), many of its other life-history traits (slow growth, large seed size, late reproductive maturity) are the opposite of those exhibited by modern plants that thrive in disturbed settings.<ref>[[#Royer|Royer ''et al''. (2003)]], p.&nbsp;92.</ref>
 
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Given the slow rate of evolution of the genus, it is possible that ''Ginkgo'' represents a pre-[[angiosperm]] strategy for survival in disturbed streamside environments. ''Ginkgo'' evolved in an era before flowering plants, when [[fern]]s, [[cycad]]s, and [[Bennettitales|cycadeoids]] dominated disturbed streamside environments, forming a low, open, shrubby canopy. The large seeds of ''Ginkgo'' and its habit of "bolting"—growing to a height of {{convert|10|m}} before elongating its side branches—may be adaptations to such an environment. Diversity in the genus ''Ginkgo'' dropped through the Cretaceous (along with that of ferns, cycads, and cycadeoids) at the same time the flowering plants were on the rise, which supports the notion that flowering plants, with their better adaptations to disturbance, displaced ''Ginkgo'' and its associates over time.<ref>[[#Royer|Royer ''et al''. (2003)]], p.&nbsp;93.</ref>
 
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{{citation needed span|text=''Ginkgo'' has been used for classifying plants with [[Leaf|leaves]] that have more than four [[Leaf#Veins|veins]] per segment, while ''[[Baiera]]'' for those with less than four veins per segment. ''[[Sphenobaiera]]'' has been used to classify plants with  broadly wedge-shaped leaves that lacks distinct leaf stems. ''[[Trichopitys]]'' is distinguished by having multiple-forked leaves with cylindrical (not flattened), thread-like ultimate divisions; it is one of the earliest fossils ascribed to the Ginkgophyta.|date=June 2013}}
 
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==Phylogeny==
 
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As of February 2013, [[Molecular phylogenetics|molecular phylogenetic studies]] have produced at least six different placements of ''Ginkgo'' relative to [[cycad]]s, [[Pinophyta|conifers]], [[Gnetophyta|gnetophytes]] and [[Flowering plant|angiosperms]]. The two most common are that ''Ginkgo'' is a sister to a [[clade]] composed of conifers and gnetophytes or that ''Ginkgo'' and cycads form a clade within the [[gymnosperm]]s. A 2013 study examined the reasons for the discrepant results, and concluded that the best support was for the [[monophyly]] of ''Ginkgo'' and cycads, these being the earliest diverging gymnosperms.<ref>[[#Wu|Wu ''et al.'' (2013)]]</ref>
 
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==References==
 
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{{reflist|21em}}
 
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===Sources===
 
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{{refbegin}}
 
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*{{cite journal |author=Dana L. Royer, Leo J. Hickey & Scott L. Wing |year=2003 |title=Ecological conservatism in the "living fossil" ''Ginkgo'' |journal=[[Paleobiology (journal)|Paleobiology]] |volume=29 |issue=1 |pages=84–104 |doi=10.1666/0094-8373(2003)029<0084:ECITLF>2.0.CO;2 |ref=Royer}}
 
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*{{cite book |author=Thomas N. Taylor & Edith L. Taylor |year=1993 |title=The Biology and Evolution of Fossil Plants |location=Englewood Cliffs, NJ |publisher=[[Prentice Hall]] |isbn=0-13-651589-4 |ref=Taylor}}
 
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*{{cite journal |author=Chung-Shien Wu, Shu-Miaw Chaw & Ya-Yi Huang |year=2013 |title=Chloroplast phylogenomics indicates that ''Ginkgo biloba'' is sister to cycads |journal=[[Genome Biology and Evolution]] |volume=5 |issue=1 |pages=243–254 |doi=10.1093/gbe/evt001 |pmid=23315384 |ref=Wu}}
 
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{{refend}}
 
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== External links ==
 
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{{Portal|Trees}}
 
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{{Medicinal herbs & fungi}}
 
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{{Ack-Wikipedia}}
 
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[[Category:Seed plants]]
 

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