| Ginkgo | |
|---|---|
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| Habit of mature tree | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnospermae |
| Division: | Ginkgophyta |
| Class: | Ginkgoopsida |
| Order: | Ginkgoales |
| Family: | Ginkgoaceae |
| Genus: | Ginkgo L.[1] |
| Type species | |
| Ginkgo biloba | |
| Species | |
| Synonyms [2] | |
SalisburiaSm. | |
Ginkgo is agenus of non-floweringseed plants, assigned to thegymnosperms. The scientific name is also used as the English common name. The order to which the genus belongs,Ginkgoales, first appeared in thePermian,[3]270 million years ago, andGinkgo is now theonly living genus within the order. Therate of evolution within the genus has been slow, and almost all its species had become extinct by the end of thePliocene. The sole surviving species,Ginkgo biloba, isfound in the wild only in China, but is cultivated around the world. The relationships between ginkgos and other groups of plants are not fully resolved.
Trichopitys heteromorpha from the earliestPermian of France, is one of the earliest fossils ascribed to the Ginkgophyta.[4] It hadmultiple-forked non-laminar leaves with cylindrical, thread-like ultimate divisions.Sphenobaiera (early Permian–Cretaceous) had wedge-shaped leaves divided into narrow dichotomously-veined lobes, lacking distinctpetioles (leaf stalks).Baiera (Triassic–Jurassic) had similar multiple-lobed leaves but with petioles.[5]: 743–756
The extant ginkgo (Ginkgo biloba) is aliving fossil, with fossils similar to the modern plant dating back to thePermian, 270 million years ago. The ancestor of the genus is estimated to have branched off from other gymnosperms about 325 million years ago, while the last common ancestor of today's only remaining species lived not earlier than 390,000 years ago.[6] The closest living relatives of theclade are thecycads.[7]
The time of thisdivergence is estimated to be extremely ancient, dating to theearly Carboniferous.[8] Fossils attributable to the genusGinkgo with reproductive organs similar to the modern species first appeared in theMiddle Jurassic,[9] and the genus diversified and spread throughoutLaurasia during theJurassic andEarly Cretaceous. At the end of thePliocene,Ginkgo fossils disappeared from thefossil record everywhere except in a small area of central China,where the modern species survived. It is doubtful whether the Northern Hemisphere fossil species ofGinkgo can be reliably distinguished. Given the slow pace of evolution andmorphological similarity between members of the genus, there may have been only one or two species existing in the Northern Hemisphere through the entirety of theCenozoic: present-dayG. biloba (includingG. adiantoides) andG. gardneri from the Palaeocene ofScotland.[10]
At least morphologically,G. gardneri and the Southern Hemisphere species are the only known post-Jurassic taxa that can be unequivocally recognised. The remainder may have beenecotypes orsubspecies. The implications would be thatG. biloba had occurred over an extremely wide range, had remarkable genetic flexibility and, thoughevolving genetically, never showed muchspeciation. While it may seem improbable that a species may exist as a contiguous entity for many millions of years, many of the ginkgo'slife-history parameters fit. It displays extreme longevity and a slow reproduction rate. Additionally, inCenozoic and later times, the ginkgo'sdistribution is wide and apparently contiguous, although steadily contracting. The fossil record shows extreme ecological conservatism as theniche of the ginkgo is restricted todisturbed streamside environments.[11]
Modern-dayGinkgo biloba grows best in well-watered and well-drained soils,[12] and the extremely similar fossilGinkgo favoured similar environments. The sediment records at the majority of fossilGinkgo localities indicate it grew primarily in disturbed environments along streams andlevees.[11]Ginkgo is therefore paradoxical in ecological terms because, while it possesses some favourable traits for living in disturbed environments (such asclonal reproduction), many of its other life-history traits (like slow growth, large seed size, late reproductive maturity) are the opposite of those exhibited by "younger",more-recently emerged plant species that thrive in disturbed settings.[13]
Given the slow rate of evolution of the genus, it is possible thatGinkgo represents a pre-angiosperm strategy for survival in disturbed streamside environments.Ginkgo evolved in an era before angiosperms (flowering plants), whenferns,cycads, andcycadeoids dominated disturbed streamside environments, forming a low, open, shrubbycanopy. The large seeds ofGinkgo and its habit of "bolting"—growing to a height ofapprox. 10 metres (30 feet) before elongating its side branches—may be adaptations to such an environment. Diversity in the genusGinkgo 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, displacedGinkgo and its associates over time.[14]
As of 2013[update],molecular phylogenetic studies have produced at least six different placements ofGinkgo relative tocycads,conifers,gnetophytes andangiosperms. The two most common are thatGinkgo is a sister to aclade composed of conifers and gnetophytes, and thatGinkgo and cycads form a clade within thegymnosperms. A 2013 study by Wu and colleagues examined the reasons for the discrepant results, finding that analysis ofnucleotide sequences was made difficult by multiple factors, but that these did not affect analysis ofamino acid sequences. The study concluded, based on the latter, that the best support was for themonophyly ofGinkgo and cycads:[15]
| Seed plants |
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The German naturalistEngelbert Kaempfer introduced the spellingginkgo in his 1712 bookAmoenitatum Exoticarum, taking it from the Japanese herbalistTekisai Nakamura [ja]'s manuscript,Kinmō Zu'i [ja], which he acquired inDejima between 1689–91. It is considered that he may have misspelledginkyo orginkio, which is aJapanese pronunciation for thekanjiJapanese:銀杏,lit. 'silver apricot',[16] asginkgo.[17]
The original Chinese name,Japanese:銀杏, appeared inChinese herbology literature such as the 1329Daily UseMateria Medica (日用本草) and the 1578Compendium of Materia Medica (本草綱目). It is ajukujikun (Chinese reading) of another Sinitic term 鴨脚 (Yājiǎo) "duckfeet" in reference to its leaves, attested in 11th centurySong dynasty literature.[18]
ThegenusGinkgo was formally described and published byCarl Linnaeus in his 1771 bookMantissa plantarum II.[1][19] He took up Kaempfer's misspelling for the name of the genus.[19][17][20] Despite its spelling, "ginkgo" is usually pronounced/ˈɡɪŋkoʊ/, which has given rise to the common alternative spelling "gingko". Thespelling pronunciation/ˈɡɪŋkɡoʊ/ is also documented in some dictionaries.[20][21]
Thefamily Ginkgoaceae was first published by the German botanistAdolf Engler in the 1897 bookDie natürlichen Pflanzenfamilien that he edited withKarl A. E. Prantl. The family contains only the genusGinkgo.[22][23] The name is anomen conservandum,[22] retained despite breaking rules of botanical nomenclature.[24]
In Korea, the seed flesh ofGinkgo biloba is eaten with rice.[25]
Ginkgolides are biologically activeterpeniclactones present inGinkgo leaves. They arediterpenoids with 20-carbon skeletons, biosynthesized fromgeranylgeranyl pyrophosphate.[26] Ginkgolide B is used in treatment ofcerebrovascular disease.[27][28] It may serve to prevent migraines in young people.[29] It functions as a selective antagonist ofglycine receptors based on noncompetitive inhibition for the neurological system.[30]
Ginkgo has been used intraditional Chinese medicine since at least the 11th century AD.[31] Ginkgo seeds, leaves, and nuts have traditionally been applied for ailments such as dementia, asthma, bronchitis, and kidney and bladder disorders. However, there is no reliable evidence that ginkgo is useful for any of these conditions.[32][33][34]
The ginkgo has appeared in culture both in East Asia and in the Western world. In China, the tree appears in ancient moulded-brick reliefs nearNanjing. In Japan, ginkgo designs appear inwoodblock prints and intsuba sword mounting decorations,[citation needed] and in thechonmage hairstyle used bysumo wrestlers.[35]
In the Western world, ginkgo designs appeared inArt Nouveau at the start of the 20th century.
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In professionalsumo, wrestlers ranked in the two highest divisions (jūryō andmakuuchi) wear an elaboratetopknot calledōichōmage (大銀杏髷;lit. 'ginkgo-leaf topknot') because it resembles the leaf of the ginkgo tree.[36]
According to some sources, the medicinal use of ginkgo dates back to 2800 B.C.… However, the first undisputed written records of ginkgo come much later… Ginkgo first appears in copies of the Shen Nung pharmacopeia around the eleventh and twelfth centuries.
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