Ginkgo biloba
Ginkgo biloba, commonly known as ginkgo, also known as the maidenhair tree, and often misspelled "gingko" 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 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. Some G. biloba trees have survived extreme events like the Hiroshima atomic bomb and others showcasing extreme longevity; G. biloba specimens have been measured in excess of 1,600 years, and the largest living trees are estimated to exceed 3,500 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 40 meters. 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 estimated to be more than 3,500 years old.Leaves
The leaves are unique among seed plants, being fan-shaped with veins radiating out into the leaf blade, sometimes bifurcating, 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.The species is heterophyllous ; those on the long shoots are thicker, have higher rates of photosynthesis, higher vein density and leaf hydraulic conductance, while those on the short shoots are better at handling drought. Leaves of long shoots are also 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. Leaves of the cultivar '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" develop on second-year growth. Short shoots have short internodes 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. 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 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 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.
Pollination
Fertilization of the ovule occurs through wind pollination, via motile sperm, as in cycads, ferns, mosses, and algae. The sperm are large 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 ovules, and development of the embryos, occurs just before or after they fall from the tree in early autumn.Fruiting and Dispersal
After fertilization, one or both ovules develop into fruit-like structures containing seeds. The fruits are 1.5–2 cm long, with a soft, fleshy, yellow-brown outer layer that is attractive in appearance, but contains butyric acid and smells foul like rancid butter or vomit when fallen. Beneath the sarcotesta is the hard sclerotesta and a papery endotesta, with the nucellus surrounding the female gametophyte at the center.Despite its perception by humans as foul, the fruit odor is attractive to certain small mammals that eat the fruit and disperse the seeds: these include the gray squirrel and, in East Asia, the palm civet and the raccoon dog. The sclerotesta resists digestion, and so the seeds are passed intact into feces, which thus provide a dispersal mechanism.
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" 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
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 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". Kaempfer's drawing can be found in Hori's article.