The Ginkgo (Ginkgo biloba; '銀杏' in Chinese), frequently misspelled as "Gingko", and also known as
the Maidenhair Tree, is a unique tree with no close living relatives. It is classified in
its own division, the Ginkgophyta, comprising the single class Ginkgoopsida, order Ginkgoales, family
Ginkgoaceae, genus Ginkgo and is the only extant species within this group. It is one of the best known examples of a living fossil. Ginkgoales are not known in the fossil record after the Pliocene,[1][verification needed] making Ginkgo biloba a
living fossil.
For centuries it was thought to be extinct in the wild, but is now known to grow in at least two small areas in
Zhejiang province in Eastern China, in the Tian Mu Shan Reserve. Ginkgo trees in these areas may have been tended and preserved by Chinese monks for
over 1000 years. [citation needed] Therefore, whether native ginkgo populations still exist is uncertain.
The relationship of Ginkgo to other plant groups remains uncertain. It has been placed loosely in the divisions
Spermatophyta and Pinophyta, but no consensus has been
reached. Since Ginkgo seeds are not protected by an ovary wall, it can morphologically be
considered a gymnosperm. The apricot-like structures produced by female ginkgo trees are technically not fruits, but are the seeds having a shell that consists of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta).
Characteristics
General Morphology
Ginkgos are very large deciduous trees, normally reaching a height of 20–35 m (66-115
feet), with some specimens in China being over 50 m (164 feet). The tree has an often angular crown and long, somewhat
erratic branches, and is usually deep rooted and resistant to wind and snow damage. Young trees are often tall and slender, and
sparsely branched; the crown becomes broader as the tree ages. During autumn, the leaves turn a bright yellow, then fall,
sometimes within a short space of time (1–15 days). A combination of resistance to disease, insect-resistant wood and the
ability to form aerial roots and sprouts makes ginkgos very long-lived, with some specimens claimed to be more than
2,500 years old: A 3,000 year-old ginkgo has been reported in Shandong province in
China.[3]
Some old Ginkgos produce aerial roots, known as chichi (Japanese; "nipples") or
zhong-ru (Mandarin Chinese), which form on the undersides of large branches and grow downwards. Chichi growth is very
slow, and may take hundreds of years to occur. The function, if any, of these thick aerial roots is unknown.
Stem
Ginkgo branches grow in length by growth of shoots with regularly spaced leaves, as seen on most trees. From the
axils of these leaves, "spur shoots" (also known as short shoots) develop on second-year growth.
Short shoots have very short internodes (so that several years' growth may only extend them by a centimeter or two) and their
leaves are ordinarily unlobed. They are short and knobby, and are arranged regularly on the branches except on first-year growth.
Because of the short internodes, leaves appear to be clustered at the tips of short shoots, and reproductive structures are
formed only on them (see picture to above left— seeds and leaves are visible on short shoots). In Ginkgos, as in other plants
that possess them, short shoots allow the formation of new leaves in the older parts of the crown. After a number of years, a
short shoot may change into a long (ordinary) shoot, or vice versa.
Leaves
The leaves are unique among seed plants, being fan-shaped with veins radiating out into the leaf
blade, sometimes bifurcating (splitting) but never anastomosing to form a network.[4] Two veins enter the leaf
blade at the base and fork repeatedly in two; this is known as dichotomous venation. The leaves are usually 5-10 cm (2-4 inches),
but sometimes up to 15 cm (6 inches) long. The old popular name "Maidenhair tree" is because the leaves resemble some of the
pinnae of the Maidenhair fern Adiantum capillus-veneris.
Leaves of long shoots are usually notched or lobed, but only from the outer surface, between the veins. They are borne both on
the more rapidly-growing branch tips, where they are alternate and spaced out, and also on the short, stubby spur shoots, where
they are clustered at the tips.
Reproduction
Female gametophyte, dissected from a seed freshly shed from the tree, containing a well-developed embryo
Ginkgos are dioecious, with separate sexes, some trees being female and others being male. Male plants produce small pollen cones with sporophylls each bearing two microsporangia spirally arranged around a central axis.
Female plants do not produce cones. Two ovules are formed at the end of a stalk, and after
pollination, one or both develop into seeds. The seed is 1.5-2 cm long. Its fleshy outer
layer (the sarcotesta) is light yellow-brown, soft, and fruit-like. It is attractive in appearance, but contains butanoic acid and
smells like rancid butter (which contains the same chemical) when fallen. Beneath the sarcotesta
is the hard sclerotesta (what is normally known as the "shell" of the seed) and a papery
endotesta, with the nucellus surrounding the female
gametophyte at the center.[5]
The fertilization of ginkgo seeds occurs via motile sperm, as in cycads, ferns, mosses and algae. The sperm are large (about
250-300 micrometres) and are similar to the sperm of cycads, which are slightly larger. Ginkgo sperm were first discovered by the
Japanese botanist Sakugoro Hirase in 1896.[6] The sperm have a complex multi-layered structure, which is a continuous belt of basal bodies that
form the base of several thousand flagella which actually have a cilia-like motion. The flagella/cilia apparatus pulls the body
of the sperm forwards. The sperm have only a tiny distance to travel to the archegonia, of which there are usually two or three.
Two sperm are produced, one of which successfully fertilizes the ovule. Although it is widely held that fertilization of ginkgo
seeds occurs just before or after they fall in early autumn,[4] [5] [7] embryos ordinarily
occur in seeds just before and after they drop from the tree.[8]
Etymology
The (older) Chinese name for this plant is 银果 yínguo ('silver fruit'). The most usual names today are 白果 bái guǒ
('white fruit') and 銀杏 yínxìng ('silver apricot'). The latter name
was borrowed in Japanese (as ichō) and Korean (as eunhaeng), when the tree itself
was introduced from China.
The scientific name Ginkgo appears to be due to a process akin to folk
etymology. Chinese characters typically have multiple pronunciations in Japanese, and the characters 銀杏 used for ichō can also be mistakenly pronounced ginkyō.
Engelbert Kaempfer, the first Westerner to see
the species in 1690, wrote down this incorrect pronunciation in his Amoenitates Exoticae
(1712); his y was misread as a g, and the misspelling stuck.[9]
Prehistory
Ginkgo adiantoides Eocene fossil leaf from the Tranquille Shale of British Columbia, Canada.
The Ginkgo is a living fossil, with fossils recognisably related to modern Ginkgo from
the Permian, dating back 270 million years. They diversified and spread throughout
Laurasia during the middle Jurassic and Cretaceous, but became much rarer thereafter. By the Paleocene, Ginkgo
adiantoides was the only Ginkgo species left in the Northern Hemisphere
(but see below) with a markedly different (but not well-documented) form persisting in the Southern Hemisphere, and at the end of the Pliocene Ginkgo
fossils disappeared from the fossil record everywhere apart from a small area of central China where the modern species survived.
It is in fact doubtful whether the Northern Hemisphere fossil species of Ginkgo can be reliably distinguished; given the
slow pace of evolution in the genus, there may have been only 2 in total; what is today called G. biloba (including G.
adiantoides), and G. gardneri from the Paleocene of Scotland.
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 just as well have simply been ecotypes or
subspecies. The implications would be that G. biloba had occurred over an extremely
wide range, had remarkable genetic flexibility and though evolving genetically never showed
much speciation. The occurrence of G. gardneri, it seems a Caledonian mountain endemic, and the somewhat greater diversity on the Southern Hemisphere, suggests that old
mountain ranges on the Northern Hemisphere could hold other, presently undiscovered, fossil Ginkgo species. Since the
distribution of Ginkgo was already relictual in late prehistoric times, the chances that ancient DNA from subfossils can shed any light on this problem seem remote. 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 (being
restricted to light soils around rivers), and a low population density.
Fossil
Ginkgo leaves from the Jurassic of England
Ginkgophyta fossils have been classified in the following families and genera:
- Ginkgoaceae
- Arctobaiera
- Baiera
- Eretmophyllum
- Ginkgo
- Ginkgoites
- Sphenobaiera
- Windwardia
- Trichopityaceae
Ginkgo has been used for classifying plants with leaves that have more than four
veins per segment, while Baiera for those with less than four veins per segment.
Sphenobaiera has been used to classify plants with a broadly wedge-shaped leaf that lacks a distinct leaf stem.
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.
Cultivation and uses
Ginkgo has long been cultivated in China; some planted trees at temples are believed to be over
1,500 years old. The first record of Europeans encountering it is in 1690 in Japanese temple
gardens, where the tree was seen by the German botanist Engelbert Kaempfer. Because of its status in Buddhism and Confucianism, the Ginkgo is also widely planted in Korea and
parts of Japan; in both areas, some naturalization has occurred, with Ginkgos seeding into natural forests.
In some areas, notably the United States, most intentionally planted Ginkgos are male
cultivars grafted onto plants propagated from seed, because the male trees will not produce the
malodorous seeds. The popular cultivar 'Autumn Gold' is a clone of a male plant.
The Ginkgo has the intriguing distinction of being one of the world's most urban-tolerant trees, often growing where other
trees cannot survive.[citation needed] Ginkgos rarely suffer disease problems, even in urban conditions, and are
attacked by few insects.[citation needed] For this reason, and for their general beauty, ginkgos are excellent urban
and shade trees, and are widely planted along many streets. The ginkgo is the official tree of the city of Kumamoto, and two leaves form the symbol of the University of
Tokyo, the main campus of which is famous for its numerous ginkgos.[citation needed]
Ginkgos are also popular subjects for growing as penjing and bonsai; they can be kept artificially small and tended over centuries. Furthermore, the trees are easy to
propagate from seed.
Extreme examples of the Ginkgo's tenacity may be seen in Hiroshima,
Japan, where four trees growing between 1–2 km from the 1945
atom bomb explosion were among the few living things in the area to survive the blast
(photos & details). While
almost all other plants (and animals) in the area were destroyed, the ginkgos, though charred, survived and were soon healthy
again. The trees are alive to this day.
Culinary use
The nut-like gametophytes inside the seeds are particularly esteemed in Asia, and are a traditional Chinese food. Called
yín xìng (银杏; literally "silver apricot") or bái guǒ
(白果; literally "white fruit"), Ginkgo nuts are used in
congee, and are often served at special occasions such as weddings and the Chinese New Year (as part of the vegetarian dish called Buddha's
delight). In Chinese culture, they are believed to have health benefits; some also consider them to have aphrodisiac qualities. Japanese cooks add Ginkgo seeds to dishes such as chawanmushi, and cooked seeds are often eaten along with other dishes. The seeds are available canned,
sold as "White Nuts", and can be found in many Asian food stores in the West. Usually only a few are added for a portion enough
for ten people.
When eaten by children, in large quantities (over 5 seeds a day), or over a long period of time, the raw gametophyte
(meat) of the seed can cause poisoning by MPN (4-methoxypyridoxine). MPN is heat-stable. Studies have demonstrated that
convulsions 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 for consumption, wearing disposable gloves. The symptoms are dermatitis or blisters similar to that caused by contact with
poison-ivy. However, seeds with the fleshy coating removed are perfectly safe to
handle.
Medical uses
The extract of the Ginkgo leaves contains flavonoid glycosides and terpenoids
(ginkgolides, bilobalides) and has been used
pharmaceutically. It has many alleged nootropic properties, and is mainly used as
memory and concentration enhancer, and anti-vertigo agent. However, studies differ about its efficacy. Some controversy has arisen over the
conclusions drawn by some studies that were allegedly funded by a firm which marketed Ginkgo. Slate, an Internet-based magazine owned by The Washington Post Company, reported in April 2007:
In 2002, a long-anticipated paper appeared in JAMA (Journal of the American Medical Association) titled "Ginkgo for memory enhancement: a randomized controlled
trial." This Williams College study, sponsored by the National Institute on Aging rather than Schwabe, examined the effects of
ginkgo consumption on healthy volunteers older than 60. The conclusion, now cited in the National Institutes of Health's ginkgo fact sheet, said: "When taken
following the manufacturer's instructions, ginkgo provides no measurable benefit in memory or related cognitive function to
adults with healthy cognitive function."
Out of the many conflicting research results, Ginkgo extract seems to have three effects on the human body: it improves blood
flow (including microcirculation in small capillaries) to most tissues and organs; it protects against oxidative cell damage from
free radicals; and it blocks many of the effects of PAF (platelet aggregation, blood clotting) that have been related to the
development of a number of cardiovascular, renal, respiratory and CNS (Central Nervous System) disorders. Ginkgo can be used for
intermittent claudication.
According to some studies, in a few cases, Ginkgo can significantly improve attention in healthy individuals[10][11]. The effect is almost immediate and reaches its peak in 2,5 hours after the intake[12].
A 2004 conference paper[13] summarizes how various trials indicate that Ginkgo shows promise in the treatment of
Alzheimer's disease, although further study is needed.
Ginkgo is commonly added to energy drinks, but the amount is typically so low it does not produce a noticeable effect, except perhaps via a placebo
effect from Ginkgo being listed on the label.
Ginkgo supplements are usually taken in the range of 40–200 mg per day.
Side effects
Ginkgo may have some undesirable effects, especially for individuals with blood circulation disorders and those taking
anti-coagulants such as aspirin and warfarin, although recent studies have found that ginkgo has little or no effect on the anticoagulant
properties or pharmacodynamics of warfarin[14][15]. Ginkgo should also not be used by people who are taking monoamine oxidase inhibitors (MAOI) or by pregnant women
without first consulting a doctor.
Ginkgo side effects and cautions include: possible increased risk of bleeding, gastrointestinal discomfort, nausea, vomiting,
diarrhea, headaches, dizziness, and restlessness. If any side effects are experienced, consumption should be stopped
immediately.
See also
References
- ^ a b
- ^ Sun (1998). Ginkgo biloba. 2006
IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Listed as Endangered (EN B1+2c v2.3)
- ^ A. Lewington & E. Parker (1999). Ancient Trees. London: Collins
& Brown Ltd. ISBN 1-85585-704-9. p. 183.
- ^ a b Ginkgoales: More on
Morphology
- ^ a b Laboratory IX -- Ginkgo, Cordaites, and the Conifers
- ^ History of Discovery of Spermatozoids In Ginkgo biloba and Cycas revoluta
- ^ Brief Notes on Ginkgo biloba
- ^ Ben F. Holt, Gar W. Rothwell. Is Ginkgo biloba (Ginkgoaceae) Really an
Oviparous Plant? American Journal of Botany, Vol. 84, No. 6 (Jun., 1997) , pp. 870-872
- ^ Faculty of
languages and cultures, Kyushu University Japan
- ^ Differential cognitive effects of Ginkgo biloba after acute and chronic
treatment in healthy young volunteers.[1]
- ^ BBC News: Herbal remedies "boost brain power".[2]
- ^ Dose-dependent cognitive effects of acute administration of Ginkgo biloba
to healthy young volunteers.[3]
- ^ L. Witkam and I. Ramzan
(2004). "Ginkgo biloba in the treatment of Alzheimer’s disease: A miracle cure?". From Cell to Society.
full text
pdf Conference page.
- ^ Xuemin Jiang et al
(2005). Effect of ginkgo and ginger on the pharmacokinetics and pharmacodynamics of warfarin in healthy subjects. British
Journal of Clinical Pharmacology 59 (4): 425–432.
- ^ Ernst E, Canter PH, Coon JT
(2005). Does ginkgo biloba increase the risk of bleeding? A systematic review of case reports. Perfusion 18:
52–56.
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