Ginkgo

The Ginkgo

(Ginkgo biloba), frequently misspelled as "Gingko," and sometimes 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 just the one species. It is one of the best known examples of a living fossil. In the past it has also been placed in the divisions Spermatophyta or Pinophyta. Ginkgo is a gymnosperm (as opposed to an angiosperm), meaning “naked seed”; its seeds are not protected by a fruit.

For centuries it was thought to be extinct in the wild, but is now known to grow wild in at least two small areas in Zhejiang province in eastern China, in the Tian Mu Shan Reserve. However, as this area has known human activity for over a thousand years, the wild status of ginkgos there is as yet uncertain.

Habit
Ginkgos are medium-large deciduous trees, reaching 20–35 m tall (some specimens in China being over 50 m), with an often angular crown and long, somewhat erratic branches. They are 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 amazing disease resistance, insect-resistant wood and the ability to form aerial roots and sprouts means that ginkgos are very long-lived, with some specimens claimed to be more than 2,500 years old.

Some old Ginkgos produce aerial roots, known as chichi (Japanese; "nipples") or zhong-ru (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.

Ginkgo branches grow in length by apical growth of "long shoots", i.e. ordinary shoots with regularly spaced leaves, as seen on most trees. These have elongated internodes, creating the regular leaf spacing, and their leaves are often bilobed. From the axils of these leaves, "spur shoots" (also known as short shoots) develop on second-year growth. Spur shoots have very short internodes (so that several years' growth may extend a spur shoot by only a centimetre or two) and their leaves are ordinarily unlobed.

These spur shoots are short and knobby, and are arranged regularly at the nodes of the long shoots (except on first-year growth). Because of the short internodes, spur shoots appear to be topped with numerous leaves, and reproductive structures are formed only on them (see picture to above left—seeds and leaves can be viewed on spur shoots). In Ginkgos, as in other plants that possess them, spur shoots allow the formation of new leaves in the older parts of the crown. After a number of years, a spur shoot may change into a long 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. Two veins enter the leaf blade at the base and fork repeatedy in two; this is known as dichotomous venation. The leaves are 5-10 cm (rarely to 15 cm) 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. During summer the leaves are a deep green, turning to brilliant yellow in the fall.

Name
The name ginkgo means "silver apricot" (銀杏, pinyin: yínxìng) in Chinese. The same characters are used in Japanese and Korean (where the ginkgo had been introduced from China). The Japanese pronunciation is ichō while the Korean equivalent is eunhang, both of which appear to be a loan from Chinese, though this is not certain (from the entry

in the dictionary Kōjien). The Japanese characters used to write ginkgo look as though they could be read ginkyō, and this was the name Engelbert Kaempfer, the first Westerner to see the species in 1690, wrote down in his Amoenitates Exoticae (1712). However, his y was misread as a g, and the misspelling stuck.

In modern Japanese, the characters are read either ichō (meaning the tree) or ginnan (meaning the seed); this latter reading appears to be based on the renjō (i.e., liaison) reading of the characters. The modern Chinese name for its shelled seeds is 白果 (Mandarin bái guǒ), meaning "white fruit".

Medical uses
The extract of the Ginkgo leaves contains flavonoid glycosides and ginkgolides and has been used pharmaceutically. It has many alleged properties, but is mainly used as memory enhancer and anti-vertigo agent. However, studies differ about its efficacy.

It is commonly added to energy drinks, but the amount is typically so low it does not produce a noticeable effect, except for the placebo effect from being listed on the label. Out of the many (conflicting) research results there seem to be basically three effects of the extract 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 (antioxidant) and 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.

A 2004 conference paper summarises how various trials indicate that Ginkgo shows promise in the treatment of Alzheimer's disease, although further study is needed.

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. It should also not be used by people who are taking the anti-depressant drugs known as monoamine oxidase inhibitors (MAOI) or by pregnant women.

Ginkgo side effects and cautions include possible increased risk of bleeding, gastrointestinal discomfort, nausea, vomiting, diarrhea, headaches, and restlessness. Ginkgo should also not be used by pregnant women or people with a blood clotting disorder without consulting a doctor first.

If any side effects are experienced the dosage should be lowered immediately. Ginkgo supplements are usually taken in the range of 40–200 mg per day. If the side effects continue usage should be stopped completely.

Other useful herb information: Boldo | Marjoram | Cascara Sagrada | Equisetum | Spikenard | Sarsaparilla | Asparagus

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Ginkgo