Ginkgo

This article is about the genus of mainly extinct trees. For its single living species, the ginkgo tree, see Ginkgo biloba. For other uses, see Ginkgo (disambiguation).

Ginkgo is a genus of non-flowering seed plants, assigned to the gymnosperms. The scientific name is also used as the English common name. The order to which the genus belongs, Ginkgoales, first appeared in the Permian,^[3] 270 million years ago, and Ginkgo is now the only living genus within the order. The rate of evolution within the genus has been slow, and almost all its species had become extinct by the end of the Pliocene. The sole surviving species, Ginkgo biloba, is found in the wild only in China, but is cultivated around the world. The relationships between ginkgos and other groups of plants are not fully resolved.

Ginkgo Temporal range: Middle Jurassic – Present PreꞒ Ꞓ O S D C P T J K Pg N
Habit of mature tree
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Gymnospermae
Division:	Ginkgophyta
Class:	Ginkgoopsida
Order:	Ginkgoales
Family:	Ginkgoaceae
Genus:	Ginkgo L.[1]
Type species
Ginkgo biloba
Species
†Ginkgo adiantoides †Ginkgo apodes Ginkgo biloba †Ginkgo cranei †Ginkgo digitata †Ginkgo dissecta †Ginkgo gardneri †Ginkgo ginkgoidea †Ginkgo henanensis †Ginkgo huolinhensis †Ginkgo huttonii †Ginkgo yimaensis
Synonyms [2]
Salisburia Sm.

Evolution

Fossil history

Fossil Ginkgo huttonii leaves from the Jurassic of England

Trichopitys heteromorpha from the earliest Permian of France, is one of the earliest fossils ascribed to the Ginkgophyta.^[4] It had multiple-forked non-laminar leaves with cylindrical, thread-like ultimate divisions. Sphenobaiera (early Permian–Cretaceous) had wedge-shaped leaves divided into narrow dichotomously-veined lobes, lacking distinct petioles (leaf stalks). Baiera (Triassic–Jurassic) had similar multiple-lobed leaves but with petioles.^{[5]: 743–756}

The extant ginkgo (Ginkgo biloba) is a living fossil, with fossils similar to the modern plant dating back to the Permian, 270 million years ago. The ancestor of the genus is estimated to have branched off from other gymnosperms about 325 million years ago, while the last common ancestor of today's only remaining species lived not earlier than 390,000 years ago.^[6] The closest living relatives of the clade are the cycads.^[7]

The time of this divergence is estimated to be extremely ancient, dating to the early Carboniferous.^[8] Fossils attributable to the genus Ginkgo with reproductive organs similar to the modern species first appeared in the Middle Jurassic,^[9] and the genus diversified and spread throughout Laurasia during the Jurassic and Early Cretaceous. At the end of the Pliocene, Ginkgo fossils disappeared from the fossil record everywhere except in a small area of central China, where the modern species survived. It is doubtful whether the Northern Hemisphere fossil species of Ginkgo can be reliably distinguished. Given the slow pace of evolution and morphological similarity between members of the genus, there may have been only one or two species existing in the Northern Hemisphere through the entirety of the Cenozoic: present-day G. biloba (including G. adiantoides) and G. gardneri from the Palaeocene of Scotland.^[10]

Evolutionary ecology

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 have 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. 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. It displays extreme longevity and a slow reproduction rate. Additionally, in Cenozoic and later times, the ginkgo's distribution is wide and apparently contiguous, although steadily contracting. The fossil record shows extreme ecological conservatism as the niche of the ginkgo is restricted to disturbed streamside environments.^[11]

Leaves in autumn

Modern-day Ginkgo biloba grows best in well-watered and well-drained soils,^[12] and the extremely similar fossil Ginkgo favoured similar environments. The sediment records at the majority of fossil Ginkgo localities indicate it grew primarily in disturbed environments along streams and levees.^[11] Ginkgo is therefore paradoxical in ecological terms because, while it possesses some favourable traits for living in disturbed environments (such as clonal reproduction), many of its other life-history traits (like slow growth, large seed size, late reproductive maturity) are the opposite of those exhibited by "younger", more-recently emerged plant species that thrive in disturbed settings.^[13]

Given the slow rate of evolution of the genus, it is possible that Ginkgo represents a pre-angiosperm strategy for survival in disturbed streamside environments. Ginkgo evolved in an era before angiosperms (flowering plants), when ferns, cycads, and cycadeoids dominated disturbed streamside environments, forming a low, open, shrubby canopy. The large seeds of Ginkgo and its habit of "bolting"—growing to a height of approx. 10 metres (30 feet) before elongating its side branches—may be adaptations to such an environment. Diversity in the genus Ginkgo dropped through the Cretaceous (along with that of ferns, cycads, and cycadeoids) at the same time the flowering plants were on the rise, which supports the notion that flowering plants, with their better adaptations to disturbance, displaced Ginkgo and its associates over time.^[14]

Phylogeny

As of 2013^[update], molecular phylogenetic studies have produced at least six different placements of Ginkgo relative to cycads, conifers, gnetophytes and angiosperms. The two most common are that Ginkgo is a sister to a clade composed of conifers and gnetophytes, and that Ginkgo and cycads form a clade within the gymnosperms. A 2013 study by Wu and colleagues examined the reasons for the discrepant results, finding that analysis of nucleotide sequences was made difficult by multiple factors, but that these did not affect analysis of amino acid sequences. The study concluded, based on the latter, that the best support was for the monophyly of Ginkgo and cycads:^[15]

Seed plants	Angiosperms (flowering plants) Gymnosperms Cycads Ginkgo Pinaceae (the pine family) Gnetophytes Cupressophytes (other conifers)

Taxonomic history and etymology

The German naturalist Engelbert Kaempfer introduced the spelling ginkgo in his 1712 book Amoenitatum Exoticarum, taking it from the Japanese herbalist Tekisai Nakamura [ja]'s manuscript, Kinmō Zu'i [ja], which he acquired in Dejima between 1689–91. It is considered that he may have misspelled ginkyo or ginkio, which is a Japanese pronunciation for the kanji Japanese: 銀杏, lit. 'silver apricot',^[16] as ginkgo.^[17]

The original Chinese name, Japanese: 銀杏, appeared in Chinese herbology literature such as the 1329 Daily Use Materia Medica (日用本草) and the 1578 Compendium of Materia Medica (本草綱目). It is a jukujikun (Chinese reading) of another Sinitic term 鴨脚 (Yājiǎo) "duckfeet" in reference to its leaves, attested in 11th century Song dynasty literature.^[18]

The genus Ginkgo was formally described and published by Carl Linnaeus in his 1771 book Mantissa plantarum II.^[1][19] He took up Kaempfer's misspelling for the name of the genus.^[19][17][20] Despite its spelling, "ginkgo" is usually pronounced /ˈɡɪŋkoʊ/, which has given rise to the common alternative spelling "gingko". The spelling pronunciation /ˈɡɪŋkɡoʊ/ is also documented in some dictionaries.^[20][21]

The family Ginkgoaceae was first published by the German botanist Adolf Engler in the 1897 book Die natürlichen Pflanzenfamilien that he edited with Karl A. E. Prantl. The family contains only the genus Ginkgo.^[22][23] The name is a nomen conservandum,^[22] retained despite breaking rules of botanical nomenclature.^[24]

Human uses

Food, medicine, and herbalism

In Korea, the seed flesh of Ginkgo biloba is eaten with rice.^[25]

Ginkgolides are biologically active terpenic lactones present in Ginkgo leaves. They are diterpenoids with 20-carbon skeletons, biosynthesized from geranylgeranyl pyrophosphate.^[26] Ginkgolide B is used in treatment of cerebrovascular disease.^[27][28] It may serve to prevent migraines in young people.^[29] It functions as a selective antagonist of glycine receptors based on noncompetitive inhibition for the neurological system.^[30]

Ginkgo has been used in traditional Chinese medicine since at least the 11th century AD.^[31] Ginkgo seeds, leaves, and nuts have traditionally been applied for ailments such as dementia, asthma, bronchitis, and kidney and bladder disorders. However, there is no reliable evidence that ginkgo is useful for any of these conditions.^[32][33][34]

Culture

The ginkgo has appeared in culture both in East Asia and in the Western world. In China, the tree appears in ancient moulded-brick reliefs near Nanjing. In Japan, ginkgo designs appear in woodblock prints and in tsuba sword mounting decorations,^{[citation needed]} and in the chonmage hairstyle used by sumo wrestlers.^[35]

• In China and Japan
• 
  Detail of moulded-brick relief "Seven Sages of the Bamboo Grove and Rong Qiqi", from a tomb near Nanjing, c. 400 AD
• 
  Ofuji, 'Miss Ginkgo', woodblock print by Kitagawa Utamaro, c. 1793–94
• 
  Tsuba sword mounting, Tobari Yoshihisa, c. 1825–1850 AD, Japan
• 
  Ginkgo hairstyle of a sumo wrestler

In the Western world, ginkgo designs appeared in Art Nouveau at the start of the 20th century.

• In Art Nouveau
• 
  Pair of fan-shaped leaves of green plique-à-jour enamel with small rose-cut diamonds in the veins. Louis Aucoc, c. 1900
• 
  Ginkgo design by Alphonse Mucha, 1901
• 
  Illustration by Anton Seder, 1903

In professional sumo, wrestlers ranked in the two highest divisions (jūryō and makuuchi) wear an elaborate topknot called ōichōmage (大銀杏髷; lit. 'ginkgo-leaf topknot') because it resembles the leaf of the ginkgo tree.^[36]