Ginkgo Nut

''Ginkgo biloba'', commonly known as ginkgo or gingko ( ), also known as the maidenhair tree, is a species of gymnosperm tree native to East Asia. It is the last living species in the order Ginkgoales, which first appeared over 290 million years ago. Fossils very similar to the living species, belonging to the genus ''Ginkgo'', extend back to the Middle Jurassic epoch approximately 170 million years ago. The tree was cultivated early in human history, remains commonly planted, and is widely regarded as a living fossil.

''G. biloba'' is a long-lived, disease-resistant, dioecious tree with unique fan-shaped leaves, capable of clonal reproduction, and known for its striking yellow autumn foliage and resilience in disturbed environments. It was known historically as “silver fruit” or “white fruit” in Chinese and called “ginkgo” due to a centuries-old transcription error. It is closely related to cycads and characterized by unique seeds that resemble apricots but are not true fruits.

''G. biloba'', once widespread but thought extinct in the wild for centuries, is now commonly cultivated in East Asia, with some genetically diverse populations possibly representing rare wild survivors in southwestern China’s mountainous regions. ''G. biloba'' has been cultivated for over a millennium across China, Korea, and Japan—often in temples—with some trees surviving extreme events like the Hiroshima atomic bomb and others living up to 1,400 years. Today it is widely planted in cities worldwide for its pollution tolerance and ornamental value.

''G. biloba'' can pose health risks including potential carcinogenicity, allergic reactions, poisoning from seeds due to ginkgotoxin, drug interactions, and adverse effects such as bleeding and neurological symptoms, especially with excessive or improper use. ''G. biloba'' wood is valued for its durability and used in crafts and sake-making, while its seeds are popular in Asian cuisine despite health risks. While widely marketed for cognitive benefits, clinical research shows limited medical effectiveness except possibly for dementia, with approval in the European Union but not by the United States Food and Drug Administration.

Description

Ginkgos are large trees, normally reaching a height of , with some specimens in China being over . The tree has an 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. A combination of resistance to disease, insect-resistant wood, and the ability to form aerial roots and sprouts makes ginkgos durable, with some specimens claimed to be more than 2,500 years old.

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 repeatedly in two; this is known as dichotomous venation. The leaves are usually , but sometimes up to long. The old common name, ''maidenhair tree'', derives from the leaves resembling 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, 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. Leaves are green both on the top and bottom and have stomata on both sides. During autumn, the leaves turn a bright yellow and then fall, sometimes within a short space of time (one to fifteen days). Leaves of the variety or forma ''G. b. tubifolia'' have funnel-shaped leaves.

Branches

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 short internodes (they may grow only one to two centimeters in several years) and their leaves are usually 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 (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.

Ginkgo prefers full sun and grows best in environments that are well-watered and well-drained. The species shows a preference for disturbed sites; in the "semiwild" stands at Tianmu Mountains, many specimens are found along stream banks, rocky slopes, and cliff edges. Accordingly, ginkgo retains a prodigious capacity for vegetative growth. It is capable of sprouting from embedded buds near the base of the trunk ( lignotubers, or basal chichi) in response to disturbances, such as soil erosion. Old specimens are also capable of producing aerial roots on the undersides of large branches in response to disturbances such as crown damage; 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 Tianmushan, 40% of the specimens surveyed were multi-stemmed, and few saplings were present.

Reproduction

''Ginkgo biloba'' is 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. Sex conversion, wherein certain branches of a tree change sexes, has been observed. This phenomenon is difficult to research because of its rarity as well as the practice of grafting female branches onto otherwise male trees that was common in 19th century Europe.

Female plants do not produce cones. Two ovules are formed at the end of a stalk, and after wind pollination, one or both develop into fruit-like structures containing seeds. The fruits are 1.5–2 cm long, with a soft, fleshy, yellow-brown outer layer (the sarcotesta) that is attractive in appearance, but contains butyric acid (also known as butanoic acid) and smells foul like rancid butter or vomit 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.

The fertilization of ginkgo seeds occurs via motile sperm, as in cycads, ferns, mosses, and algae. The sperm are large (about 70–90 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. 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 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. Fertilization of ginkgo seeds occurs just before or after they fall in early autumn. Embryos may develop in the seeds before or after they drop from the tree.

Genome

Chinese scientists published a draft genome of ''Ginkgo biloba'' in 2016. The tree has a large genome of 10.6 billion DNA nucleobase "letters" (the human genome has three billion) and about 41,840 predicted genes which enable a considerable number of antibacterial and chemical defense mechanisms. 76.58% of the assembled sequence turned out to be repetitive sequences.

In 2020, a study in China of ginkgo trees up to 667 years old showed little effects of aging, finding that the trees continued to grow with age and displayed no genetic evidence of senescence, and continued to make phytochemicals indefinitely.

Phytochemicals

Extracts of ginkgo leaves contain phenolic acids, proanthocyanidins, flavonoid glycosides, such as myricetin, kaempferol, isorhamnetin, and quercetin, and the terpene trilactones ginkgolides and bilobalides. The leaves also contain unique ginkgo biflavones, alkylphenols, and polyprenols.

Taxonomy

The older Chinese name for this plant is 銀果, meaning "silver fruit", pronounced ''yínguǒ'' in Mandarin or ''Ngan-gwo'' in Cantonese. The current commonly used names are 白果 (), meaning "white fruit", and (), meaning "silver apricot". The name 銀杏 was translated into Japanese as イチョウ () or ぎんなん () and into Korean as 은행 ().

Carl Linnaeus described the species in 1771, the specific epithet ''biloba'' derived from the Latin ''bis'', "twice" and ''loba'', "lobed", referring to the shape of the leaves. Two names for the species recognise the botanist Richard Salisbury, a placement by Nelson as ''Pterophyllus salisburiensis'' and the earlier ''Salisburia adiantifolia'' proposed by James Edward Smith. The epithet of the latter may have been intended to denote a characteristic resembling '' Adiantum'', the genus of maidenhair ferns.

The scientific name ''Ginkgo'' is the result of a spelling error that occurred three centuries ago. ''Kanji'' typically have multiple pronunciations in Japanese, and the characters 銀杏 used for ''ginnan'' can also be pronounced ''ginkyō''. Engelbert Kaempfer, the first Westerner to investigate the species in 1690, wrote down this pronunciation in the notes that 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 other Japanese words containing the syllable "kyō" into account, a more precise romanization following his writing habits would have been "ginkio" or "ginkjo". Linnaeus, who relied on Kaempfer when dealing with Japanese plants, adopted the spelling given in Kaempfer's "Flora Japonica" (''Amoenitates Exoticae'', p. 811). Kaempfer's drawing can be found in Hori's article.

Classification

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 its 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 seeds that have a shell consisting of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta). The sarcotesta has a strong smell that most people find unpleasant.

The ginkgo 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, because Ginkgoales other than ''G. biloba'' are not known from the fossil record after the Pliocene