Pronunciation key ( giŋ′kō ) |
ging•ko
[ giŋ′kō ]
n.
[pl. GINGKOES (-kōz)], a ginkgo.
gink•go
n.
[pl. GINKGOES (-kōz)]
[Japan. ginko, gingko < Chinese yin-hing, silver apricot].
- A large tree with fan-shaped leaves and edible yellow fruit native to northern China and Japan.
maid•en•hair
[mād′ʼn-hâr′]
n.
- Any of a group of ferns with delicate fronds and slender stalks: also called maidenhair fern.
- The ginko. Maidenhair tree
The Maidenhair Tree (Ginkgo biloba) is of a monotypic genus, the only living representative of an extensive ancient Order of conifer-like trees. It is neither a broadleafed, 'flowering' tree nor a conifer. It is a Ginkgo and the only remaining member in an Order of plants which were a worldwide, dominant tree form around 150 million years ago and are unrelated to any living plant. The Ginkgo is the most primitive extant land plant which evolved during a time in Earth history when a branching, network system of veins had not yet became available among plants. Therefore, a broad leaf from a close fan of radiating veins was developed. Similar to the most primitive conifers, the opposing genders, male and female, are on separate trees with one distinguishing characteristic, it sheds it leaves in winter. Ginkgo was named for the Japanese word for the plant and nuts. The nut has a silver color. The word ginkgo derives from the Chinese and Japanese words for silver nut or silver apricot.
| Taxonomic Hierarchy | |
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| Kingdom | Plantae – Vegetal, plants |
| Subkingdom | Viridaeplantae – green plants |
| Infrakingdom | Streptophyta – land plants |
| Division | Tracheophyta – vascular plants, tracheophytes |
| Subdivision | Spermatophytina – spermatophytes, seed plants |
| Infradivision | Gymnospermae – gymnosperms, gymnospermes, gimnosperma |
| Class | Ginkgoopsida – ginkgo |
| Order | Ginkgoales |
| Family | Ginkgoaceae |
| Genus | Ginkgo L. – ginkgo |
| Species | Ginkgo biloba L. – maidenhair tree, common ginkgo |
Ginkgo biloba is the only remaining (extant) species of the family Ginkgoaceae which were Gymnosperms that existed around 175-200 million years ago. It is a medium-sized, deciduous tree which matures to about 36-40
meters (120-130 ft) in height and 2.5 meters (8 feet) in diameter. The fan-shaped leaves have two lobes and parallel veins. Male trees produce cones and the female produce pairs of ovules or seeds on the ends of the flower stalk. Upon ripening, the fleshy seeds fall to the ground and produce a foul odor. |
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The Maidenhair Tree is sacred in the traditions of Buddhist religion and was cultivated for many centuries in China and Japan. It was rediscovered long ago growing in temple gardens of China where the sacred trees were carefully tended and perpetuated. It became known to Western science in the eighteenth century when the first specimens were introduced in Europe. Historically it was believed the species was saved from extinction through cultivation in the Far East, but now good evidence exists for believing the species occurs in a wild state at the borders of Chekiang and Anhwei provinces in southeastern China. (In 1956, a small population of Ginkgo trees were reported growing in a wild state.) This was claimed to be the last natural refuge for the once prominent constituent of Mesozoic and early Tertiary floras of the Northern Hemisphere.
For the past 250 years the tree has been planted widely and grown successfully under many different conditions of soil and climate. Remarkably the species appears to be free of disease and resistant to pests (fungus and insects) and air pollution.
 A-C: Evolution of ginkgophyte leaves. Jurassic. A-C redrawn from Harris, 1935. D Ginkgo digitata. Jurassic. Redrawn from Paleobotany and the Evolution of Plants, 2nd Edition, Cambridge University Press ©1993 |
The Order Ginkgoales flourished primarily during the Mesozoic era, achieving its greatest evolutionary developments during the Jurassic period (about 150 million years ago) when dinosaurs dominated the earth. The genus Ginkgo itself probably extends back to this period. The group was very rich in diversity, some of them certainly represent distinct genera. Ginkgo enjoyed a worldwide distribution and no doubt important constituents of the flora. Fossil leaf remains are often found abundantly in detaic sediments laid down during the Mesozoic. Ginkgo declined toward the close of the Mesozoic era. This decline continued during the Tertiary and today only one species remains making it a monotypic genus. Seward observed in 1919, "Ginkgo biloba L., has a preeminent claim to be described in Darwin's words as a living fossil."
According to Encyclopedia Britannica Micropedia ©1984:
"...the only living representative of the order Ginkogoales, a group of gymnosperms composed of the family Ginkogoaceae, approximately 15 genera that date from the Permian Period of the Paleozoic Era, some 225,000,000 to 280,000,000 years ago. Extinct genera, such as Ginkgoites and Baiera, are known from fossilized leaves that are similar to those of the present-day tree."
Botanists have referred to it as a "missing link" between flowering plants and ferns.
The habit of Ginkgo is similar to Glossopteris and some conifers, with a main trunk which bears branches with axillary long and short shoots. Characteristically, often reniform to fan-shaped leaves. They have slender and long petioles (stalks) and scattered on the shoots or crowded at the distal ends of the slowly-maturing short shoots, and are covered with leaf scars. Ginkgo forms a massive tree, and old specimens, some having estimated to have lived more than one thousand years old developed to a very large size. In the juvenile tree there is often a strong leader, forming the main trunk. Branches are somewhat straggly, giving the tree its rather distinctive appearance during the winter season in its leafless condition.
Ginkgo in winter. Edited and redrawn from Tet Borsig, Collier's Encyclopedia ©1960
Ginkgo leaves are peculiar, having a wedge-shaped leaf blade borne on a long-stalk (petiole). Venation consists of an open forking system that lack vein fusions. The delicate fern-like foliage and shape of the lamina account for the tree's English popular name of "Maidenhair Tree". The leathery leaves are up to eight centimeters (three inches) in length, and often twice as broad. Dull gray green to yellow green in summer, and in the early or middle autumn, the foliage turns a brilliant shade of pale yellow, then to a rich gold and some more on the side of a pale orange before breaking off late in the season.
(paraphrased)"If a paleobotanist were to find a fossil leaf from a short and long shoot, they may be inclined to group them as different species. Not everyone would take cognizance of such possible variations when describing individual fossils and other structures." |
Ginkgo shows a considerably variegated size and form in its foliage ranging from a bilobed leaf to those of rapidly growing long shoots where the lamina which are deeply divided into cuneate segments, or those of short shoots where the smaller leaves may have margins that are entire.
Ginkgo consist separately of male and female trees. It appears most earlier specimens planted in Europe, were male. The first female specimen was recorded to have grown near Geneva in 1814. Some trees in cultivation have had branches of the opposite sex grafted onto them.
Pollen-bearing cones are not especially distinctive, being similar to the male cones of conifers in a general way. Seeds are usually produced in pairs but often on stalks that appear to be morphologically equivalent to the male cones. Both are carried on leafy dwarf-shoots. There are no female cones among Ginkgo comparable to conifers. The females bear ovules on megasporophylls and males develop pollen on microssporophylls. Pollination is effected by wind.
It shares only a few features in common with cycads, the dwarfish, hard-leafed palm-like plants notably cultivated along the Gulf Coast which bear central cone-like structures, however it remains completely unrelated in any direct way to cycads or any other extant plant or tree species. The most remarkable feature of the reproductive cycle in Ginkgo is the presence of sperm (swimming male cells) similar to those of cycads. Several features of seed development are similar in cycads and Ginkgo. However, this does not indicate a close relationship, rather it indicates similarity in primitive features retained by these extraordinary ancient and primitive plant species.
Ginkgos grow well in many temperate regions with exception to cold northern regions. Ginkgo are fairly impartial to soil type, as long as it is fertile, and grow best in a sunny location. They make for imposing trees and are often planted in avenues. They are tolerant of pollution, therefore make useful trees to cultivate in industrial areas. Cultivars available include 'Fastigiata,' a columnar form with semierect branches, 'Pendula,' with weeping branches, and 'Tremonia,' which as a conical form.
Female trees bear paired ovules that when fertilized develop into yellowish, plumlike seeds about 2.5 centimeters (1 inch) in length, and consist of a large nut surrounded by a fleshy outer covering. The nut itself is silver colored. |
The fissured bark is gray in color, deeply furrowed on older trees and has a corky texture. The light-colored wood, soft and weak has limited economic value.
Ripe ovules, or the mature seeds, have a soft, yellowish-orange fleshy outer layer. Fruit is abundant on female trees. When located in populated areas they tend to be tread on and create a messy pulp underfoot which notably has an unpleasant odor of rancid butter. Also, notably the female trees tend to bear long, low, sinuous branches which would block traffic while the male tend to be slender and tall. For this reason male trees are usually preferred for avenue planting, though in some locations males and females are planted side by side, the same shape. In the Orient, when cleansed and washed it produces a pure white seed kernel consisting of an inner oval nut which contains a sweet, oily, edible seed that is sometimes roasted and eaten, and traditionally regarded as an edible delicacy.
Evolutionary Development and Decline
The origins of Ginkgoales appear to be with Paleozoic ancestry which by the end of the Triassic became an important part of Mesozoic floras. During the Jurassic, especially the Middle Jurassic, the Ginkgoales reached the height of their numbers in species variation and worldwide distribution. A survey of Jurassic and Cretaceous localities shows us that the ginkophytes were circumpolar, making appearances in Alaska, Greenland, Scandanavia, Franz Joseph Land, Siberia, and Mongolia. The Siberian locations have proved extremely productive. Locations in western Canada and the continental United States have rendered fossilized leaf remains of Ginkgoites from the Upper Mesozoic and Lower Tertiary deposits. Locales in Patagonia south to the tip of South America, South Africa, India, Australia and New Zealand bear witness that Ginkgoales were not confined exclusively to those regions that are now a part of the Northern Hemisphere. Many areas are known in Europe, including those in England, Scotland, Germany, Italy, Hungary, Turkestan and Afghanistan. Many locations have been noted by Seward in 1919, and Harris in 1974. Toward the close of the Cretaceous, the Ginkgoales were in decline, not only in worldwide distribution but in the number of genera and species.
During the Tertiary a decline of ginkgophytes has been recorded. By the beginning of the Oligocene epoch only 2 out of about 19 species remained. One of these is Ginkgo adiantoides, though not abundant, has been found in parts of western Canada in the Upper Cretaceous-Tertiary (Paleocene) deposits. In the Eocene, fossils of G. adiantoides have been more abundantly recovered, which suggests a cooling trend favorable to wider dispersal into locations which include Alaska, Alberta, British Columbia, Montana, South Dakota and Wyoming. The paucity of G. adiantoides preserved during the Oligocene attests to a sharp decline that continued into the Miocene of western North America. During the Miocene the species disappeared from the fossil record in that part of the world. But in Europe, it is reported to have continued to proliferate into the Pliocene. Since that time, our present evidence indicates Ginkgoales has been represented only by the one extant monotypic "living fossil" known as Ginkgo biloba.
Mesozoic and Tertiary Ginkgoales
The abundance of fossilized compression-imprinted leaves available to paleobotany from the Mesozoic and Tertiary deposits have presented diverse problems in their identification and assigning names to species. One author suggested that it might be appropriate to assign all species of ginkgophyte forms into two or three species instead of the many that have been described in literature over past decades.
Most experts disagree on grounds this is a poor solution and would not properly express the great diversity that occurred within the group, especially during the Jurassic. Since the introduction of studies by Harris in 1935, on Ginkgo-like leaf compression-impression fossils utilizing the characteristics of epidermal and stomatal structures, it is possible with well-preserved material to distinguish what appear to be defined species.
Distinction among genera however, still offers significant problems of nomenclature. Many authors follow the system used by Seward in 1919, who used the genus Ginkgoites for all fossil leaves sharing similarity with Ginkgo biloba although indistinguishable from the extant species. This system however gives rise to the presumption that Ginkgo did not have a fossil record. In an effort to avoid this erroneous approach, some investigators have included those leaf fossils that are indistinguishable from leaves of the modern Ginkgo in the genus but used different species names. Those fossilized Ginkgo-like leaf remains, which can be distinguished from Ginkgo by their morphological and anatomical characteristics, are placed by Harris and Florin (1935 and 1936) in the genus Ginkgoites.
During the Mesozoic both Ginkgo and Ginkgoites leaves are widely distributed, those of Ginkgoites appearing in the late Triassic are far more abundant in Mesozoic rocks. Ginkgo fossils appear in the Jurassic but became much more extensive during the Tertiary. Of the seven or eight Mesozoic leaf genera included in the Ginkgoales (Harris, 1935, 1974) the two having the largest number of species are Ginkgoites and Baiera.
Reproductive Structures
In 1976, Hughes emphasized in his work that what we search for in the fossil record for discoveries about the ginkophyte reproductive structures are strongly influenced by what we already know of Ginkgo biloba. That is neglecting to remember that Jurassic and Cretaceous ginkogophytes were highly diversified and one species can not be universally representative of the extinct varieties. Therefore it is likely that fructifications belonging to ginkgophytes that have been recovered and documented but have failed to be correctly recognized. The ovulate structures of Ginkgo biloba can provide only some clues as to the morphology of other, extinct fossilized forms.
 Abnormal development of Ginkgo biloba ovulate structures. A Ovule formed on expanded lamina of a leaf. |
Associated with the Jurassic and Cretaceous, some Ginkgo-like remains of ovules named Allicospermum (Harris, 1935) which bear resemblance to ovules of Ginkgo biloba and cycads. Karkenia (1965) from the Cretaceous of Argentina, consists of over 100 or more small ovules crowded on a short stalk. Each of the ovules possesses a projecting microphyl and a short pedicel. The fructifications are associated with Ginkgoites tigrensis and considered to belong to the same species.
Fossilized material from the Yorkshire Jurassic beds have contributed a lot to current knowledge about ginkgophyte fructifications. In 1976, Harris was able to report paired ovules joined by a pad of tissue with Ginkgo-like stomata. These occur in beds with abundant Ginkgoites huttoni where a search for pollen organs of the Ginkgo type was rewarded (van Konijnenburg-van Cittert, 1971). The organ is a small pollen-bearing catkin with pairs of microsporangia on the tips of relatively lax stalks attached to an axis about 5 mm. long. The fossilized pollen sample obtained from it was monocolpate and similar to G. biloba. Only a few other verified fossilized ginkophyte reproductive structures have been recovered.
