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Ginkgo Biloba
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4/30/14, 1:05 PMGinkgo biloba - Wikipedia, the free encyclopedia
Page 1 of 24http://en.wikipedia.org/wiki/Ginkgo_biloba
Ginkgo bilobaGinkgo (Ginkgo biloba; in Chinese, Korea and Japanese: ��, pinyin romanization:yín xìng, Hepburn romanization: ichō or ginnan, Vietnamese: bạch quả), also spelled
gingko[3] and also known as the maidenhair tree, is a unique species of tree with noliving relatives. The ginkgo is a living fossil, recognisably similar to fossils dating back
270 million years. Native to China,[4] the tree is widely cultivated and was introducedearly to human history. It has various uses in traditional medicine and as a source offood.
Description
Ginkgos are large trees, normally reaching a height of20–35 m (66–115 feet), with some specimens in Chinabeing over 50 m (164 feet). The tree has an angularcrown and long, somewhat erratic branches, and isusually deep rooted and resistant to wind and snowdamage. Young trees are often tall and slender, andsparsely branched; the crown becomes broader as the tree ages. During autumn, theleaves turn a bright yellow, then fall, sometimes within a short space of time (one to15 days). A combination of resistance to disease, insect-resistant wood and the ability toform aerial roots and sprouts makes ginkgos long-lived, with some specimens claimed tobe more than 2,500 years old.
Ginkgo is a relatively shade-intolerant species that (at least in cultivation) grows best inenvironments that are well-watered and well-drained. The species shows a preferencefor disturbed sites; in the "semiwild" stands at Tian Mu Shan, many specimens arefound along stream banks, rocky slopes, and cliff edges. Accordingly, ginkgo retains aprodigious capacity for vegetative growth. It is capable of sprouting from embeddedbuds near the base of the trunk (lignotubers, or basal chi chi) in response todisturbances, such as soil erosion. Old individuals are also capable of producing aerial
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roots on the undersides of large branches in response to disturbances such as crowndamage; these roots can lead to successful clonal reproduction upon contacting the soil.These strategies are evidently important in the persistence of ginkgo; in a survey of the"semiwild" stands remaining in Tian Mu Shan, 40% of the specimens surveyed were
multistemmed, and few saplings were present.[5]
Branches
Ginkgo branches grow in length by growth of shoots with regularly spaced leaves, asseen on most trees. From the axils of these leaves, "spur shoots" (also known as shortshoots) develop on second-year growth. Short shoots have very short internodes (so theymay grow only one or two centimeters in several years) and their leaves are usuallyunlobed. They are short and knobby, and are arranged regularly on the branches excepton first-year growth. Because of the short internodes, leaves appear to be clustered at thetips of short shoots, and reproductive structures are formed only on them (see picturesbelow - seeds and leaves are visible on short shoots). In ginkgos, as in other plants thatpossess them, short shoots allow the formation of new leaves in the older parts of thecrown. After a number of years, a short shoot may change into a long (ordinary) shoot,
or vice versa.[citation needed]
Leaves
The leaves are unique among seed plants, being fan-shaped with veins radiating out intothe leaf blade, sometimes bifurcating (splitting), but never anastomosing to form a
network.[6] Two veins enter the leaf blade at the base and fork repeatedly in two; this isknown as dichotomous venation. The leaves are usually 5–10 cm (2–4 in), butsometimes up to 15 cm (6 in) long. The old popular name "maidenhair tree" is becausethe leaves resemble some of the pinnae of the maidenhair fern, Adiantum capillus-veneris. Ginkgos are prized for their autumn foliage, which is a deep saffron yellow.
Leaves of long shoots are usually notched or lobed, but only from the outer surface,
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between the veins. They are borne both on the morerapidly growing branch tips, where they are alternateand spaced out, and also on the short, stubby spurshoots, where they are clustered at the tips.
Reproduction
Ginkgos are dioecious, with separate sexes, some treesbeing female and others being male. Male plants producesmall pollen cones with sporophylls, each bearing twomicrosporangia spirally arranged around a central axis.
Female plants do not produce cones. Two ovules areformed at the end of a stalk, and after pollination, one orboth develop into seeds. The seed is 1.5–2 cm long. Itsfleshy outer layer (the sarcotesta) is light yellow-brown,soft, and fruit-like. It is attractive in appearance, but
contains butyric acid[7] (also known as butanoic acid)
and smells like rancid butter or vomit[8] when fallen.Beneath the sarcotesta is the hard sclerotesta (the "shell"of the seed) and a papery endotesta, with the nucellus
surrounding the female gametophyte at the center.[9]
The fertilization of ginkgo seeds occurs via motile sperm, as in cycads, ferns, mosses and
algae. The sperm are large (about 70–90 micrometres)[10] and are similar to the spermof cycads, which are slightly larger. Ginkgo sperm were first discovered by the Japanese
botanist Sakugoro Hirase in 1896.[11] The sperm have a complex multi-layered structure,which is a continuous belt of basal bodies that form the base of several thousand flagellawhich actually have a cilia-like motion. The flagella/cilia apparatus pulls the body of thesperm forwards. The sperm have only a tiny distance to travel to the archegonia, of
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which there are usually two or three. Two sperm are produced, one of which successfullyfertilizes the ovule. Although it is widely held that fertilization of ginkgo seeds occurs
just before or after they fall in early autumn,[6][9] embryos ordinarily occur in seeds just
before and after they drop from the tree.[12]
Ginkgo pollen-bearing cones
Ovules ready for fertilization
Female gametophyte, dissected from a seed freshly shed from the tree, containing awell-developed embryo
Immature ginkgo ovules and leaves
Autumn leaves and fallen seeds
A forest of saplings sprout among last year's seeds
Distribution and habitat
Although Ginkgo biloba and other species of the genus were once widespreadthroughout the world, its range shrank until by two million years ago, it was restricted toa small area of China. For centuries, it was thought to be extinct in the wild, but is nowknown to grow in at least two small areas in Zhejiang province in eastern China, in theTian Mu Shan Reserve. However, recent studies indicate high genetic uniformity amongginkgo trees from these areas, arguing against a natural origin of these populations andsuggesting the ginkgo trees in these areas may have been planted and preserved by
Chinese monks over a period of about 1,000 years.[13] This study demonstrates a greatergenetic diversity in Southwestern China populations, supporting glacial refugia in
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mountains surrounding eastern Qinghai-Tibet Plateau, where several old-grow,
candidates to wild populations have been reported.[13][14] Whether native ginkgopopulations still exist has not been demonstrated unequivocally, but evidence growsfavouring these Southwestern populations as wild, from genetic data but also fromhistory of those territories, with bigger Ginkgo biloba trees being older than
surrounding human settlements.[13]
Where it occurs in the wild, it is found infrequently in deciduous forests and valleys onacidic loess (i.e. fine, silty soil) with good drainage. The soil it inhabits is typically in the
pH range of 5.0 to 5.5.[15]
In many areas of China, it has been long cultivated, and it is common in the southern
third of the country.[15] It has also been commonly cultivated in North America for over200 years and in Europe for close to 300, but during that time, it has never become
significantly naturalized.[16]
Taxonomy and naming
The species was initially described by Linnaeus in 1771, the specific epithet biloba
derived from the Latin bis, 'two' and loba, 'lobed', referring to the shape of the leaves.[17]
Two names for the species recognise the botanist Richard Salisbury, a placement byNelson as Pterophyllus salisburiensis and the earlier Salisburia adiantifolia proposedby James Edward Smith. The epithet of the latter may have been intended to denote a
characteristic resembling Adiantum, the genus of maidenhair ferns.[18]
The relationship of ginkgo to other plant groups remains uncertain. It has been placedloosely in the divisions Spermatophyta and Pinophyta, but no consensus has beenreached. Since its seeds are not protected by an ovary wall, it can morphologically beconsidered a gymnosperm. The apricot-like structures produced by female ginkgo treesare technically not fruits, but are seeds that have a shell consisting of a soft and fleshy
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section (the sarcotesta), and a hard section (the sclerotesta).
The ginkgo is classified in its own division, the Ginkgophyta, comprising the single classGinkgoopsida, order Ginkgoales, family Ginkgoaceae, genus Ginkgo and is the onlyextant species within this group. It is one of the best-known examples of a living fossil,because Ginkgoales other than G. biloba are not known from the fossil record after the
Pliocene.[19][20]
Etymology
The older Chinese name for this plant is ��, meaning "silver fruit", nowadayspronounced as yínguǒ in Mandarin. The most usual names today are �� (bái guǒ),meaning "white fruit", and �� (yínxìng), meaning "silver apricot". The former namewas borrowed directly in Vietnamese as bạch quả. The latter name was borrowed inJapanese ���� (ginnan) and Korean �� (eunhaeng), when the tree itself wasintroduced from China.
The scientific name Ginkgo is the result of a spelling error that occurred three centuriesago. Chinese characters typically have multiple pronunciations in Japanese, and thecharacters �� used for ginnan can also be pronounced ginkyō. Engelbert Kaempfer,the first Westerner to investigate the species in 1690, wrote down this pronunciation inhis notes he later used for the Amoenitates Exoticae (1712) with the "awkward" spelling"ginkgo". This appears to be a simple error of Kaempfer, taking his spelling of otherJapanese words containing the syllable "kyō" into account, a more precise romanization
following his writing habits would have been "ginkio" or "ginkjo".[21] Linné, who reliedon Kaempfer when dealing with Japanese plants adopted the spelling given inKaempfer's "Flora Japanica" (Amoenitates Exoticae, p. 811).
Palaeontology
The ginkgo is a living fossil, with fossils recognisably related to modern ginkgo from thePermian, dating back 270 million years. The most plausible ancestral group for the order
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Ginkgoales is the Pteridospermatophyta, also known as the "seed ferns", specifically the
order Peltaspermales. The closest living relatives of the clade are the cycads,[22] whichshare with the extant G. biloba the characteristic of motile sperm. Fossils attributable tothe genus Ginkgo first appeared in the Early Jurassic, and the genus diversified andspread throughout Laurasia during the middle Jurassic and Early Cretaceous. Itdeclined in diversity as the Cretaceous progressed, and by the Paleocene, Ginkgoadiantoides was the only Ginkgo species left in the Northern Hemisphere, while amarkedly different (and poorly documented) form persisted in the SouthernHemisphere. At the end of the Pliocene, Ginkgo fossils disappeared from the fossilrecord everywhere except in a small area of central China, where the modern speciessurvived. It is doubtful whether the Northern Hemisphere fossil species of Ginkgo canbe reliably distinguished. Given the slow pace of evolution and morphological similaritybetween members of the genus, there may have been only one or two species existing inthe Northern Hemisphere through the entirety of the Cenozoic: present-day G. biloba
(including G. adiantoides) and G. gardneri from the Paleocene of Scotland.[23]
At least morphologically, G. gardneri and the Southern Hemisphere species are the onlyknown post-Jurassic taxa that can be unequivocally recognised. The remainder mayhave been ecotypes or subspecies. The implications would be that G. biloba had occurredover an extremely wide range, had remarkable genetic flexibility and, though evolvinggenetically, never showed much speciation. While it may seem improbable that a speciesmay 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; (inCenozoic and later times) a wide, apparently contiguous, but steadily contractingdistribution coupled with, as far as can be demonstrated from the fossil record, extreme
ecological conservatism (restriction to disturbed streamside environments).[24]
Modern-day G. biloba grows best in environments that are well-watered and drained,[25] and the extremely similar fossil Ginkgo favored similar environments: the sedimentrecord at the majority of fossil Ginkgo localities indicates it grew primarily in disturbed
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environments along streams and levees.[24] Ginkgo, therefore, presents an "ecologicalparadox" because while it possesses some favorable traits for living in disturbedenvironments (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.[26]
Given the slow rate of evolution of the genus, Ginkgo possibly represents apreangiosperm strategy for survival in disturbed streamside environments. Ginkgoevolved in an era before flowering plants, when ferns, cycads, and cycadeoids dominateddisturbed streamside environments, forming low, open, shrubby canopies. Ginkgo'slarge seeds and habit of "bolting" - growing to a height of 10 m before elongating its sidebranches - may be adaptions to such an environment. Because diversity in the genusGinkgo drops through the Cretaceous (along with that of ferns, cycads, and cycadeoids)at the same time the flowering plants were on the rise, the notion that flowering plantswith better adaptations to disturbance displaced Ginkgo and its associates over time is
supported.[27]
Ginkgo has been used for classifying plants with leaves that have more than four veinsper segment, while Baiera for those with fewer than four veins per segment.Sphenobaiera has been used to classify plants with a broadly wedge-shaped leaf thatlacks a distinct leaf stem. Trichopitys is distinguished by having multiple-forked leaveswith cylindrical (not flattened), thread-like ultimate divisions; it is one of the earliest
fossils ascribed to the Ginkgophyta.[citation needed]
Extant Ginkgo biloba[28]
Cultivation and uses
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Ginkgo has long been cultivated in China; some plantedtrees at temples are believed to be over 1,500 years old.The first record of Europeans encountering it is in 1690in Japanese temple gardens, where the tree was seen bythe German botanist Engelbert Kaempfer. Because of itsstatus in Buddhism and Confucianism, the ginkgo is alsowidely planted in Korea and parts of Japan; in bothareas, some naturalization has occurred, with ginkgosseeding into natural forests.
In some areas, most intentionally planted ginkgos are male cultivars grafted onto plantspropagated from seed, because the male trees will not produce the malodorous seeds.The popular cultivar 'Autumn Gold' is a clone of a male plant.
Ginkgos adapt well to the urban environment, tolerating pollution and confined soil
spaces.[29] They rarely suffer disease problems, even in urban conditions, and are
attacked by few insects.[30][31] For this reason, and for their general beauty, ginkgos areexcellent urban and shade trees, and are widely planted along many streets.
Ginkgos are also popular subjects for growing as penjing and bonsai;[32] they can bekept artificially small and tended over centuries. Furthermore, the trees are easy topropagate from seed.
The ginkgo leaf is the symbol of the Urasenke school of Japanese tea ceremony. The treeis the national tree of China, and is the official tree of the Japanese capital of Tokyo, andthe symbol of Tokyo is a ginkgo leaf.
Hiroshima
Extreme examples of the ginkgo's tenacity may be seen in Hiroshima, Japan, where sixtrees growing between 1–2 km from the 1945 atom bomb explosion were among the few
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living things in the area to survive the blast.[33] While almost all other plants (andanimals) in the area were destroyed, the ginkgos, though charred, survived and weresoon healthy again. The trees are alive to this day.
Culinary use
The nut-like gametophytes inside the seeds areparticularly esteemed in Asia, and are a traditionalChinese food. Ginkgo nuts are used in congee, and areoften served at special occasions such as weddings andthe Chinese New Year (as part of the vegetarian dishcalled Buddha's delight). In Chinese culture, they arebelieved to have health benefits; some also considerthem to have aphrodisiac qualities. Japanese cooks add
ginkgo seeds (called ginnan) to dishes such as chawanmushi, and cooked seeds areoften eaten along with other dishes.
When eaten in large quantities or over a long period, especially by children[34] thegametophyte (meat) of the seed can cause poisoning by 4'-O-methylpyridoxine (MPN).
MPN is heat stable and not destroyed by cooking.[34] Studies have demonstrated theconvulsions caused by MPN can be prevented or terminated with pyridoxine.
Some people are sensitive to the chemicals in the sarcotesta, the outer fleshy coating.These people should handle the seeds with care when preparing the seeds forconsumption, wearing disposable gloves. The symptoms are allergic contact
dermatitis[35][36] or blisters similar to that caused by contact with poison ivy. However,
seeds with the fleshy coating removed are mostly[clarification needed][quantify] safe tohandle.
Potential medicinal uses
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Extracts of ginkgo leaves contain flavonoid glycosides
(myricetin and quercetin)[37] and terpenoids (ginkgolides,bilobalides) and have been used pharmaceutically. Theseextracts are shown to exhibit reversible, nonselectivemonoamine oxidase inhibition, as well as inhibition ofreuptake at the serotonin, dopamine, and norepinephrinetransporters, with all but the norepinephrine reuptake
inhibition fading in chronic exposure.[38] Ginkgo extract hasin addition been found to act as a selective 5-HT1A receptor
agonist in vivo.[39] Ginkgo supplements are usually taken inthe range of 40–200 mg per day. In 2010, a meta-analysis of clinical trials has shown
Ginkgo to be moderately effective in improving cognition in dementia patients[40] but
not preventing the onset of Alzheimer's disease in people without dementia.[41][42] Inresearch not yet confirmed by clinical or governmental agencies, ginkgo may have some
efficacy in treating the symptoms of schizophrenia.[43][44][45][46][47][48][49]
As a memory and concentration enhancement
Ginkgo is believed to have nootropic properties, and is mainly used as memory and
concentration enhancer, and antivertigo agent.[50] However, studies differ about itsefficacy. The largest and longest independent clinical trial to assess Ginkgo bilobapublished the finding in 2008 that the supplement does not reduce incidence of all-cause dementia or Alzheimer's disease in adults 75 years or older who had normalcognition or mild cognitive impairment when given a twice-daily dose of 120 mg extract
of G. biloba.[51][52] However, a similar trial published in December 2010 concluded thesame extract formulation of G. biloba (EGb 761), when given as a single 240-mg dailydose, "was found significantly superior to placebo in the treatment of patients with
dementia with neuropsychiatric symptoms" in a trial with 410 out-patients.[53]
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According to some studies, Ginkgo can significantly improve attention in healthy
individuals.[54][55] In one such study, the effect was almost immediate and reaches its
peak 2.5 hours after the intake.[56]
One study suggests ginkgo's purported effect on cognition may be attributable to its
inhibitory effect on norepinephrine reuptake.[38]
Nonetheless, a meta-analysis in 2012[57] reported zero effect sizes for the impact ofGinkgo biloba on memory, attention and problem-solving in healthy individuals.
In dementia
Ginkgo has been studied as a possible treatment for Alzheimer's disease. Preliminarystudies were encouraging, but the current understanding is that Ginkgo is not an
effective treatment or preventative for Alzheimer's.[40][58] Research began with positive
preclinical results in mice,[59] and a 2006 study found 160 mg of ginkgo extract to be aseffective as a daily 5-mg dose of the cholinesterase inhibitor donepezil in human
subjects.[60] A 2008 randomized controlled clinical trial found ginkgo ineffective at
treating dementia in humans at a daily dose of 120 mg.[61][62] A similar trial publishedin 2010, however, found ginkgo effective at treating mild to moderate dementia at the
higher single dose of 240 mg daily.[53] Another randomized controlled trial, published in2009, found no benefit from ginkgo in preventing cognitive decline or dementia when
given at a dose of 120 mg twice daily.[42] A similar study reported in 2012 concluded thelong-term use of Ginkgo biloba extract does not affect progression to Alzheimer's
disease.[63] A recent meta-analysis of 9 studies of ginkgo for use in the treatment ofdementia concluded it was more effective than placebo, although, like other dementia
drugs, the clinical significance of these moderate effects was difficult to quantify.[40] Aneditorial in The Lancet concluded ginkgo biloba does not prevent dementia in elderlyindividuals with or without memory complaints or cognitive impairment and is not
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effective for prevention of Alzheimer's disease.[58]
In other symptoms
Of the many conflicting results from basic research, ginkgo extract may have threeeffects on the human body: improvement in blood flow to most tissues and organs,protection against oxidative cell damage from free radicals, and blockage of many of the
effects of platelet-activating factor (platelet aggregation, blood clotting)[64] that havebeen related to the development of a number of cardiovascular, renal, respiratory andcentral nervous system disorders. Ginkgolides, especially ginkgolide B, are potentantagonists against platelet-activating factor, and thus may be useful in protection and
prevention of thrombus, endotoxic shock, and from myocardial ischemia.[65]
Ginkgo has been studied as a potential treatment for sexual dysfunction related to SSRI
use, but failed to show any effectiveness in placebo-controlled trials.[66][67]
The World Health Organization[68] reported possible medicinal uses of Ginkgo bilobashown in preliminary clinical research include treatment of the effects of mild to
moderate cerebrovascular insufficiency[69] and of peripheral arterial occlusive diseases.[70] Cerebrovascular insufficiency, i.e. insufficient blood flow to the brain, may manifestitself as memory deficit, disturbed concentration or headaches. Other preliminarystudies failed to show any effect of ginkgo on cognitive function in patients with multiple
sclerosis.[71]
Side effects
Ginkgo may have undesirable effects, especially for individuals with blood circulationdisorders and those taking anticoagulants such as aspirin or warfarin, although recentstudies have found ginkgo has little or no effect on the anticoagulant properties or
pharmacodynamics of warfarin in healthy subjects.[72] Ginkgo inhibits monoamine
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oxidase,[73] so people who are taking certain types of antidepressants (such asmonoamine oxidase inhibitors and selective serotonin reuptake inhibitors), as well as
pregnant women, may experience side effects.[74][75]
Additional side effects include increased risk of bleeding, gastrointestinal discomfort,nausea, vomiting, diarrhea, headaches, dizziness, heart palpitations, and restlessness.[75][76]
Ginkgo biloba preparations have shown some carcinogenic effects in animal models, but
they are not classified as human carcinogens.[77][78][79] The lowest observed dosagesthat caused adverse effect in these animal studies were at 100 mg/kg, and thus dosagesthat are impossible to reach by the consumption of Ginkgo Biloba preparations. Aside ofpossible complications in combination with anti-coagulant drugs, standardizedpreparations of Ginkgo biloba are safe, and side effects are rare.
Allergic precautions and contraindications to use
Some authors claim that Ginkgo biloba extracts, which are co-administered withanticoagulant drugs such as warfarin or coumadin, increase the risk for bleeding due totheir assumed antiplatelet activity. Concerns that standardized Ginkgo bilobapreparations (GBE) significantly impact haemostasis or adversely affect the safety of
anticoagulant drugs are however not supported by current medical literature.[80]
The presence of amentoflavone in G. biloba leaves would indicate a potential forinteractions with many medications through the strong inhibition of CYP3A4 andCYP2C9; however, no empirical evidence supports this. Further, at recommended doses,studies have shown, "[m]ultiple-dose administration of Ginkgo biloba did not affect
cytochrome P-450 2D6 or 3A4 activity in normal volunteers."[81] The concentration ofamentoflavone found even in commercial ginkgo extracts possibly is too low to bepharmacologically active.
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Ginkgo biloba leaves and sarcotesta also contain ginkgolic acids,[82] which are highly
allergenic, long-chain alkylphenols such as bilobol or adipostatin A[83] (bilobol is asubstance related to anacardic acid from cashew nut shells and urushiols present in
poison ivy and other Toxicodendron spp.)[36] Individuals with a history of strongallergic reactions to poison ivy, mangoes, cashews and other alkylphenol-producingplants are more likely to experience allergic reaction when consuming non-standardizedginkgo-containing preparations, combinations, or extracts thereof. The level of theseallergens in standardized pharmaceutical preparations from Ginkgo biloba wasrestricted to 5 ppm by the Commission E of the former Federal German HealthAuthority.
Review of chemicals in G. biloba
The plant also contains biflavones[84] Important constituents present in the medicinallyused leaves are the terpene trilactones, i.e., ginkgolides A, B, C, J and bilobalide, manyflavonol glycosides, biflavones, proanthocyanidins, alkylphenols, simple phenolic acids,
6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols.[85]
See also
André Michaux, introduced the ginkgo to North AmericaGinkgo/Wanapum State Park in central Washington, USAHerbalismList of edible seeds
References
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External links
Growing Ginkgoes from seed: by the Ottawa Horticultural SocietyGymnosperm DatabaseUniversity of California Museum of PaleontologyGinkgo biloba information (Plants for a Future)Ginkgo: MedlinePlus Supplements - U.S. National Library of MedicineGinkgo biloba Overview - University of Maryland Medical Center