Ginkgo biloba

• 1. Introduction

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  Ginkgo biloba is a tree that lived through the atomic bomb dropped on Hiroshima in 1945 and simply kept growing. Six ginkgos there were among the few living things in the area to survive the blast. Almost every other plant and animal nearby was killed. The ginkgos were charred, yet they recovered and were soon healthy again. They are counted among the hibakujumoku, the trees that survived the bomb, and all six are still alive.

  That toughness is only the start of what makes this East Asian species strange. It is the last living species of its entire order, with no sibling left to share its family tree. So how did one species outlast all of its kin? Why do people on several continents plant it, guard it and cook with it? And do the extracts sold in its name deliver what the labels promise?

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• 2. Deep Time

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  The oldest fossil that looks recognisably like ginkgo comes from France. It is called Trichopitys, and it dates to the very start of the Permian, more than 290 million years ago. Fossils that belong to the genus Ginkgo itself first show up in the Middle Jurassic, about 170 million years ago. Through the Jurassic and the Early Cretaceous the genus diversified and spread across Laurasia.

  Then came a long decline. As the Cretaceous went on, ginkgos lost diversity, and so did ferns, cycads and cycadeoids, while flowering plants rose. One hypothesis says the flowering plants, better adapted to disturbance, pushed these older groups aside. By the Paleocene, Ginkgo adiantoides was the only Ginkgo species left in the Northern Hemisphere. A markedly different and poorly documented form lingered in the Southern Hemisphere.

  Even that count of species may be too generous. Northern Hemisphere fossils are hard to tell apart, because the genus evolved slowly and kept much the same shape. There may have been only one or two species across the whole Cenozoic. One is the living G. biloba, which would include G. adiantoides. The other is G. gardneri, from the Paleocene of Scotland. If that is right, a single species once ranged very widely, stayed genetically flexible, and never split into many.

  Its habits help explain why. Ginkgo evolved before flowering plants, when ferns, cycads and cycadeoids formed low, open, shrubby canopies along disturbed streams. Its large seeds, and a habit of bolting up to 10 meters before sending out side branches, may have suited that world. Sediments at most fossil sites show it grew in disturbed ground such as streamsides.

  Yet scientists call the tree an ecological paradox. Plants that thrive on disturbed ground usually grow fast, make small seeds and mature early. Ginkgo does the opposite, with slow growth, large seeds and late maturity. Only its clonal reproduction fits the usual pattern.

  At the end of the Pliocene, ginkgo fossils vanished everywhere except one small area of central China. The living species survived there. Its nearest living relatives today are the cycads.

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• 3. Anatomy of a Ginkgo

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  Some ginkgos in China stand more than 40 meters tall, which is 131 feet. Most reach a more modest 20-35 meters. Young trees are tall, slender and sparsely branched, and the crown broadens as they age. Mature trees have an angular crown with long, somewhat erratic branches, and deep roots that resist wind and snow.

  The leaf is the real signature. No other seed plant has one like it. Each leaf is a fan, with veins radiating through the blade, sometimes splitting in two but never joining into a network. Two veins enter at the base and fork repeatedly, a pattern called dichotomous venation. Leaves are usually 5-10 centimeters long, and occasionally reach 15.

  The leaves of the maidenhair fern, Adiantum capillus-veneris, have small leaflets called pinnae. The ginkgo's leaves resemble them, and that resemblance gave the tree its old common name, maidenhair tree.

  A single ginkgo carries two kinds of leaf, a condition called heterophylly. Leaves on long shoots are thicker, photosynthesise faster, and have denser veins and better water conductance. Leaves on short shoots cope better with drought. Long-shoot leaves are often notched or lobed, though only from the outer edge and between veins. The cultivar 'Tubifolia' even has funnel-shaped leaves.

  The short shoots, also called spur shoots, develop on second-year growth. Some grow only one to two centimeters in several years, so their leaves bunch at the tips. Seeds and other reproductive structures form only on these knobby spurs. They let the tree produce fresh leaves deep inside the older parts of the crown.

  Each autumn the leaves, green on both faces with stomata on both sides, turn a deep saffron yellow. Then they drop, sometimes within as little as one to fifteen days. A short shoot can later become a long shoot, or the other way around, so the roles are not fixed for life.

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• 4. Built to Persist

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  On Tianmushan, in the semiwild stands, researchers found that 40 percent of the surveyed ginkgos had several stems. Few saplings were present at all. The pattern says a great deal about how the species hangs on. Ginkgo favors disturbed ground, and many Tianmu trees grow on stream banks, rocky slopes and cliff edges.

  The tree meets disturbance with regrowth. When soil erodes, it can sprout from buds buried near the base of the trunk, in swellings called lignotubers. Old specimens grow aerial roots on the undersides of large branches after crown damage. If such a root reaches the soil, it can start a clone. Add disease resistance and insect-resistant wood, and the result is a tree measured at over 1,600 years old, with the largest estimated at more than 3,500.

  In 2016, Chinese scientists published a draft genome. It holds about 10.6 billion DNA letters, compared with three billion in the human genome. It also holds about 41,840 predicted genes, which power many antibacterial and chemical defenses. Repetitive sequences make up 76.58 percent of the assembled sequence.

  A Chinese study in 2020 looked at ginkgos up to 667 years old. The trees kept growing with age and showed no genetic sign of senescence. They also went on making phytochemicals indefinitely. Leaf extracts contain phenolic acids, proanthocyanidins and flavonoid glycosides such as myricetin, kaempferol, isorhamnetin and quercetin. They also contain terpene trilactones called ginkgolides and bilobalides.

  Inside its cells the tree hides one more oddity. Ginkgo is the only vascular plant known to host a green microalga as an endosymbiont. The partnership is inherited from parent to offspring, and it has been found in trees in Asia, North America and Europe. The alga sits in an immature form with no functional chloroplast, so it does not photosynthesise. It may still take part in the host's metabolism.

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• 5. Seeds and Smell

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  The Japanese botanist Sakugoro Hirase discovered ginkgo sperm in 1896. They are large, about 70-90 micrometres, and they swim, as sperm do in cycads, ferns, mosses and algae. Cycad sperm are slightly larger still. A continuous belt of basal bodies anchors several thousand flagella, which beat with a cilia-like motion and pull the sperm forward. The journey is tiny, since the archegonia are usually only two or three. Two sperm form, and only one fertilizes the ovule.

  Ginkgo trees come in separate sexes. Male trees carry small pollen cones, and each sporophyll bears two microsporangia arranged spirally around a central axis. Female trees make no cones. Instead, two ovules form at the end of a stalk, and wind carries the pollen to them. Fertilization and early embryo growth happen just before or after the ovules fall, in early autumn.

  Some branches have been seen to change sex. The rarity of this makes it hard to study. Research is also muddied by a nineteenth-century European habit of grafting female branches onto male trees.

  After fertilization, one or both ovules ripen into fruit-like structures, 1.5-2 centimeters long. They are not true fruits but seeds. The outer layer, the sarcotesta, is soft, fleshy and yellow-brown, and looks inviting. It contains butyric acid, and once fallen it smells like rancid butter or vomit. Under it lies a hard shell, the sclerotesta, then a papery endotesta around the central female gametophyte.

  Humans find the odor foul, but certain small mammals find it attractive. The gray squirrel eats the fruit and spreads the seeds. In East Asia the palm civet and the raccoon dog do the same. The sclerotesta resists digestion, so the seeds emerge intact in droppings.

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• 6. Planted by Hand

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  For centuries, ginkgo was thought to be extinct in the wild. Today it is a common cultivated tree across eastern China, Korea and Japan. Ginkgos across these regions show high genetic uniformity, and some Chinese scholars suggest monks planted and preserved them over about 1,000 years. Populations in southwestern China are more diverse. That points to glacial refugia in the mountains around the eastern Tibetan Plateau, where several old-growth candidates for wild populations have been reported.

  Whether truly native populations remain has not been shown beyond doubt. Genetic evidence suggests the southwestern groups may be wild, and the largest and oldest trees may predate nearby human settlements. Where it does occur in the wild, ginkgo grows infrequently in deciduous forests and valleys, on well-drained acidic loess with a pH of 5.0-5.5. The wild climate is mostly temperate.

  In China, ginkgo is common across the southern third of the country, and some temple trees are believed to be over 1,500 years old. Buddhism and Confucianism helped carry it to Korea and Japan, where it has been widely planted since the 14th century. In both places it has seeded itself into natural forests. North America has cultivated it for over 200 years and Europe for close to 300, yet it has never become significantly naturalized in either.

  At the Tsurugaoka Hachimangū shrine in Kamakura, Kanagawa Prefecture, an ancient ginkgo stands beside the stone entry staircase. Legend says it has been there since the shrine's founding around 1063. It is nicknamed kakure-ichō, the hiding ginkgo. An Edo-period legend claims the shōgun Minamoto no Sanetomo was assassinated in 1219 by his nephew Kugyō, who hid behind this tree.

  Scholars have since shown that ginkgos reached Japan from China in the 14th century. A tree-ring measurement in 1990 put the kakure-ichō at about 500 years old. On the 10th of March 2010, a storm blew the tree down. The stump has since sprouted vigorously.

  At the Buddhist temple of Gu Guanyin in the Zhongnan Mountains, a ginkgo is reputed to be 1,400 years old. It is a popular tourist attraction.

  Cities love the species for practical reasons. Ginkgos tolerate pollution and cramped soil, rarely suffer disease, and are attacked by few insects. Growers often plant male cultivars grafted onto seed-grown rootstock, because male trees drop no foul seeds. 'Autumn Gold' is a clone of a male plant. But male pollen is highly allergenic, with an OPALS rating of 7 out of 10, against 2 for female trees. Female cultivars include 'Liberty Splendor', 'Santa Cruz' and 'Golden Girl', all of which release no pollen. In the UK the compact 'Troll' has won the Royal Horticultural Society's Award of Garden Merit. Gardeners also train ginkgos as penjing and bonsai, small enough to tend for centuries.

  The leaf has become an emblem across East Asia. It is the symbol of the Urasenke school of Japanese tea ceremony, and the symbol of Tokyo itself, whose official tree is the ginkgo. The University of Tokyo has used two ginkgo leaves on its badge since 1948, a design by Shoichi Hoshino, which became the university logo in 2004 after a redesign. Osaka University has used a simplified leaf since 1991, created by the designer Ikko Tanaka for the university's sixtieth anniversary. Sungkyunkwan University in South Korea also uses the leaf as an emblem. In professional sumo, wrestlers in the two top divisions, jūryō and makuuchi, wear a topknot styled after the ginkgo leaf. Seoul has counted the ginkgo as an official tree since 1971.

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• 7. A Misspelled Name

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  Engelbert Kaempfer, a German botanist, was the first Westerner to investigate the tree, in 1690 in Nagasaki, where he saw it in Japanese temple gardens. His notes later fed into his book Amoenitates Exoticae, published in 1712, which spelled the name "ginkgo". By his own habits with similar Japanese syllables, he should have written "ginkio" or "ginkjo". For a long time scholars blamed an error by Kaempfer. Nagata and colleagues showed the spelling came from his interpreter, Genemon Imamura, who spoke the Nagasaki dialect.

  The Japanese side of the puzzle lies in the characters 銀杏. Kanji often carry several readings, and these can be read as ginnan or as ginkyō. Chinese herbal works such as the Daily Use Materia Medica of 1329 and the Compendium of Materia Medica of 1578 used the characters. The tree's older Chinese name is 銀果, meaning silver fruit. The common modern names are 白果, white fruit, and 銀杏, silver apricot. During the Song dynasty, 銀杏 was the term used for tribute purposes, in place of 鴨脚, meaning duckfeet, a nod to the leaves, in northeast China where the tree grew. Japanese turned it into イチョウ or ぎんなん, and Korean into 은행.

  Carl Linnaeus described the species in 1771. He relied on Kaempfer for Japanese plants and adopted his spelling, so the oddity became the genus name. The epithet biloba comes from the Latin bis, meaning twice, and loba, meaning lobed, a reference to the leaves. Most people say the name as GINK-oh, which is why the variant "gingko" is common. Two other names honor the botanist Richard Salisbury. James Edward Smith proposed Salisburia adiantifolia, and Nelson placed the tree as Pterophyllus salisburiensis.

  Taxonomists have placed ginkgo in its own division, Ginkgophyta, with a single class Ginkgoopsida, order Ginkgoales and family Ginkgoaceae. Its seeds have no ovary wall around them, so it counts morphologically as a gymnosperm. Beyond that, no agreement has been reached. It has been placed loosely in the divisions Spermatophyta and Pinophyta, and neither placement has won consensus.

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• 8. Table, Medicine and Risk

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  The wood of Ginkgo biloba is fire-resistant and slow to decay. Craftsmen use it for furniture, chessboards, carving and casks for making saké.

  In Asian kitchens the kernels are esteemed. Chinese cooks put ginkgo nuts in congee and serve them at weddings and at the Chinese New Year, as part of the vegetarian dish called Buddha's delight. Japanese cooks add the seeds, called ginnan, to dishes such as chawanmushi. Salted, grilled ginkgo nuts are a popular snack at izakayas, served with beer. In Korea the nuts are stir-fried and eaten, or used to garnish foods such as sinseonro.

  Chinese medicine has used ginkgo since at least the 11th century CE. Seeds, leaves and nuts were applied to ailments including dementia, asthma, bronchitis, and kidney and bladder disorders. There is no conclusive evidence that it helps with any of them.

  The seeds also carry risks. In large quantities or over a long period, they may cause poisoning by ginkgotoxin, known as MPN, a compound that cooking does not destroy. A few case reports describe convulsions, which limited studies found were eased by pyridoxine phosphate, a form of vitamin B6. Overeating the seeds can also deplete vitamin B6. Handling the fleshy coating can cause allergic contact dermatitis, with blisters like those of poison ivy. The cause is ginkgolic acids, related to compounds in cashew shells and poison ivy. German health authorities restricted them in standardized pharmaceutical preparations to 5 ppm.

  Supplements bring their own side effects, including a higher risk of bleeding, nausea, headaches, dizziness and heart palpitations. They may disturb the dosing of anticoagulants such as warfarin. Since 2016, the International Agency for Research on Cancer has classed ginkgo extract as a possible human carcinogen, in group 2B.

  The evidence for memory benefits is thin. A 2023 review found too little clinical evidence to support ginkgo as a therapy. The United States National Center for Complementary and Integrative Health says it has never been conclusively proven effective for any condition. Systematic reviews found no benefit for high blood pressure, tinnitus, post-stroke recovery or altitude sickness.

  Results for dementia are mixed. In 2014 the European Medicines Agency's herbal committee judged leaf extract effective and safe for mild dementia, and the EU lists it as an herbal medicine. A 2021 umbrella review found it may help people with Alzheimer's disease, but a 2023 analysis found the evidence insufficient. A 2026 Cochrane review found little or no benefit for mild cognitive impairment, and small, low-certainty gains in dementia symptoms. A 2016 review concluded the extract reduced tardive dyskinesia symptoms in people with schizophrenia.

  Between 2021 and 2023, the US Food and Drug Administration sent warning letters to ginkgo supplement makers for false health claims and for misbranding products as unapproved drugs.

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