Ginkgoes are very large trees, normally reaching a height of 20–35 m (66–115 feet), with some specimens in China being over 50 m (164 feet). 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. During autumn, the leaves turn a bright yellow, then fall, sometimes within a short space of time (1–15 days). A combination of resistance to disease, insect-resistant wood and the ability to form aerial roots and sprouts makes ginkgos long-lived, with some specimens claimed to be more than 2,500 years old.
Ginkgo is a relatively shade-intolerant species that (at least in cultivation) grows best in environments that are well-watered and well-drained. The species shows a preference for disturbed sites; in the "semi-wild" stands at Tian Mu Shan, 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 chi chi) in response to disturbances, such as soil erosion. Old individuals are also capable of producing aerial roots (chi chi) 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 "semi-wild" stands remaining in Tian Mu Shan, 40% of the Ginkgo specimens surveyed were multi-stemmed, and few saplings were present.[SUP][3][/SUP]
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 very short internodes (so they may grow only one or 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 (see pictures below - 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. [edit]Leaves
The leaves are unique among seed plants, being fan-shaped with veins radiating out into the leaf blade, sometimes bifurcating (splitting) but never anastomosingto form a network.[SUP][4][/SUP] Two veins enter the leaf blade at the base and fork repeatedly in two; this is known as dichotomous venation. The leaves are usually 5–10 cm (2-4 inches), but sometimes up to 15 cm (6 inches) long. The old popular name "Maidenhair tree" is because the leaves resemble some of the pinnae of the Maidenhair fernAdiantum 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. [edit]Reproduction
Ginkgos are dioecious, with separate ***es, 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.
Female plants do not produce cones. Two ovules are formed at the end of a stalk, and after pollination, one or both develop into seeds. The seed is 1.5–2 cm long. Its fleshy outer layer (the sarcotesta) is light yellow-brown, soft, and fruit-like. It is attractive in appearance, but containsbutanoic acid[SUP][5][/SUP] (also known as butyric acid) and smells like rancid butter or vomit[SUP][6][/SUP] when fallen. Beneath the sarcotesta is the hardsclerotesta (the "shell" of the seed) and a papery endotesta, with the nucellus surrounding the female gametophyte at the center.[SUP][7][/SUP]
The fertilization of ginkgo seeds occurs via motile sperm, as in cycads, ferns, mosses and algae. The sperm are large (about 250-300 micrometres) and are similar to the sperm of cycads, which are slightly larger. Ginkgo sperm were first discovered by the Japanese botanistSakugoro Hirase in 1896.[SUP][8][/SUP] 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 actually 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. Although it is widely held that fertilization of ginkgo seeds occurs just before or after they fall in early autumn,[SUP][4][/SUP][SUP][7][/SUP] embryos ordinarily occur in seeds just before and after they drop from the tree.[SUP][9][/SUP]
Ginkgo pollen-bearing cones
Ovules ready for fertilization
Female gametophyte, dissected from a seed freshly shed from the tree, containing a well-developed embryo
Immature ginkgo ovules and leaves
Autumn leaves and fallen seeds
A forest of saplings sprout among last year's seeds
The species was initially described by Linnaeus in 1771, the specific epithet biloba derived from the Latinbis 'two' and loba 'lobed', referring to the shape of the leaves.[SUP][13][/SUP] Two names for the species recognise the botanist Richard Salisbury, a placement by Nelson as Pterophyllus salisburiensis and the earlierSalisburia 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.[SUP][14][/SUP]
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 Ginkgo 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 that consists of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta).
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.[SUP][15][/SUP][SUP][16][/SUP]
[h=3][edit]Etymology[/h]The older Chinese name for this plant is 銀果 ('silver fruit'), nowadays pronounced as yínguǒ in Mandarin. The most usual names today are 白果 bái guǒ ('white fruit') and 銀杏 yínxìng ('silver apricot'). The former name was borrowed directly in Vietnamese (as bạch quả). The latter name was borrowed in Japanese (as ぎんなん "ginnan") and Korean (as 은행 "eunhaeng"), when the tree itself was introduced from China.
The scientific name Ginkgo appears to be due to a process akin to folk etymology. Chinese characterstypically have multiple pronunciations in Japanese, and the characters 銀杏 used for ginnan can also be pronounced ginkyō. Engelbert Kaempfer, the first Westerner to see the species in 1690, wrote down this pronunciation in his Amoenitates Exoticae (1712) with the "awkward" spelling "Ginkgo". This appears to be a simple error of Kaempfer, taking his spelling of other Japanese words into account, a more preciseromanization would have been "Ginkio" or "Ginkjo".[SUP][17][/SUP]
[h=2][edit]Palaeontology[/h]
Ginkgo bilobaEocene leaf from the MacAbee, B.C., Canada.
The Ginkgo is a living fossil, with fossils recognisably related to modern Ginkgo from the Permian, dating back 270 million years. The most plausible ancestral group for the order Ginkgoales is the Pteridospermatophyta, also known as the "seed ferns," specifically the order Peltaspermales. The closest living relatives of the clade are the cycads,[SUP][18][/SUP] which share with the extant G. biloba the characteristic of motile sperm. Fossils attributable to the genus Ginkgo first appeared in the Early Jurassic, and the genus diversified and spread throughout Laurasia during the middle Jurassic and Early Cretaceous. It declined in diversity as the Cretaceous progressed, and by the Paleocene, Ginkgo adiantoides was the only Ginkgo species left in the Northern Hemisphere while a markedly different (and poorly documented) form persisted in the Southern Hemisphere. 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 ofGinkgo 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 Paleocene of Scotland.[SUP][19][/SUP]
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 orsubspecies. 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. These are: extreme longevity; slow reproduction rate; (in Cenozoic and later times) a wide, apparently contiguous, but steadily contracting distribution coupled with, as far as can be demonstrated from the fossil record, extreme ecological conservatism (restriction to disturbed streamside environments).[SUP][20][/SUP]
Fossil Ginkgo leaves from the Jurassic of England
Modern-day G. biloba grows best in environments that are well-watered and drained,[SUP][21][/SUP] and the extremely similar fossil Ginkgo favored similar environments: the sediment record at the majority of fossil Ginkgo localities indicates it grew primarily in disturbed environments along streams and levees.[SUP][20][/SUP] Ginkgo therefore presents an "ecological paradox" because while it possesses some favorable traits for living in disturbed environments (clonal reproduction) many of its other life-history traits (slow growth, large seed size, late reproductive maturity) are the opposite of those exhibited by modern plants that thrive in disturbed settings.[SUP][22][/SUP]
Given the slow rate of evolution of the genus, it is possible that Ginkgo represents a pre-angiospermstrategy for survival in disturbed streamside environments. Ginkgo evolved in an era before flowering plants, when ferns, cycads, and cycadeoids dominated disturbed streamside environments, forming a low, open, shrubby canopy. Ginkgo's large seeds and habit of "bolting" - growing to a height of 10 m before elongating its side branches - may be adaptions to such an environment. The fact that diversity in the genus Ginkgo drops through the Cretaceous (along with that of ferns, cycads, and cycadeoids) at the same time that flowering plants were on the rise, supports the notion that flowering plants with better adaptations to disturbance displaced Ginkgo and its associates over time.[SUP][23][/SUP] Ginkgo has been used for classifying plants with leaves that have more than four veins per segment, while Baiera for those with fewer than four veins per segment. Sphenobaiera has been used to classify plants with a broadly wedge-shaped leaf that lacks a distinct leaf stem. Trichopitysis distinguished by having multiple-forked leaves with cylindrical (not flattened) thread-like ultimate divisions; it is one of the earliest fossils ascribed to the Ginkgophyta.
[h=2][edit]Cultivation and uses[/h]Ginkgo has long been cultivated in China; some planted trees at temples are believed to be over 1,500 years old. The first record of Europeans encountering it is in 1690 in Japanese temple gardens, where the tree was seen by the German botanist Engelbert Kaempfer. Because of its status in Buddhism and Confucianism, the Ginkgo is also widely planted in Korea and parts of Japan; in both areas, some naturalization has occurred, with Ginkgos seeding into natural forests.
In some areas, most intentionally planted Ginkgos are male cultivars grafted onto plants propagated from seed, because the male trees will not produce the malodorous seeds. The popular cultivar 'Autumn Gold' is a clone of a male plant.
Ginkgos adapt well to the urban environment, tolerating pollution and confined soil spaces.[SUP][24][/SUP] They rarely suffer disease problems, even in urban conditions, and are attacked by few insects.[SUP][25][/SUP][SUP][26][/SUP] For this reason, and for their general beauty, ginkgos are excellent urban and shade trees, and are widely planted along many streets.
Ginkgos are also popular subjects for growing as penjing and bonsai; they can be kept artificially small and tended over centuries. Furthermore, the trees are easy to propagate from seed.
