Ginkgo Trees

Ginkgo Trees

Ginkgo biloba is the last surviving species of Ginkgophyta, a phylum of long-lived, vascular plants that evolved during the Permian period some 250 million years ago. Ginkgo trees, once thought extinct, are sometimes called living fossils due to the strong resemblance between the modern form and ancient remains preserved in the geo­logic record. The popularity of ornamental ginkgo trees in Asia has led to their widespread cultiva­tion and dissemination.

Ginkgos are medium-large trees that can live for hundreds of years, attaining a height of 30 meters and a trunk diameter of 2 meters. A few exceptional specimens may exceed 1,000 years in age and proportions far in excess of these. They comprise a unique division of the gymnosperms, an important seed-bearing plant group that includes cycads, conifers, and ferns. Ginkgos are easily recognized by their leaves, which look like a two-lobed fan (hence biloba).

Ginkgos are dioecious plants, meaning that male and female reproductive organs are borne on separate trees. Male trees form a small cone that produces motile sperm. On the female tree, fertil­ized seeds mature into a tan, fleshy fruit 25-40 millimeters long. These fruits are rich in butyric acid, which when crushed can release an odor likened to rancid butter. These sorts of naturally occurring chemicals in the tree are thought to have evolved for better resistance to insects and bacteria, or even to help ward off herbivores.

Ginkgophyta trees arose during the Permian, approximately 250 million years ago, and to the present day have left numerous fossils of their distinctive leaves, stems, seeds, and wood. After their emergence the group continued to spread and diversify, surviving the relatively arid Triassic to form part of the great forests of the Jurassic when the genus Ginkgo itself first evolved—ap- proximately 170 million years ago. Since the end of the Cretaceous, the ginkgo has suffered from a steady constriction of its range, abundance, and diversity. The precise reasons are unknown, but today the ginkgo is all but extinct in the wild; a few small native populations remain in the Zhejiang province of China, scattered in elevated broadleaved forests.

In some ways, the ginkgo has been reclaiming its former territory. In China the trees have long been cultivated in the gardens of Buddhist temples (and occasionally as a food source). From there they spread to Japan, and in the 17th century to Europe and other Western countries. In modern cities all over the world, they have become a shade tree of choice. The ginkgo is well suited to the urban landscape, as it requires minimal mainte­nance. It also has a high tolerance for pollution and resistance against disease.

Ginkgo seeds are used in traditional Asian medicine, and the cooked seeds can even be eaten. More recently, ginkgo leaf extract has been pack­aged to treat a variety of ailments. This utilizes the plant’s naturally occurring concentration of fla­vonoids, a group of antioxidants found in certain fruits and vegetables. Although scientific research has not yet supported the health benefits attrib­uted to ginkgo, some promising lines of pharma­ceutical research are investigating its effects on dementia and Alzheimer’s disease.

Ginkgos are true icons of long-term survival; their modern form is quite similar to that of fossils 250 million years old. The tree has survived tram­pling hordes of herbivorous dinosaurs and major environmental catastrophes. Its extremely limited native populations, however, testify to enormous ecological pressure—the ginkgo has been strug­gling to survive in the present era. In the wild their relatively inefficient reproductive system, slow regeneration, and lack of diversity have exacer­bated the damage from habitat loss. Ginkgo biloba faces a very high risk of extinction in the wild; it is currently classified as an endangered species. After successfully adapting to nature’s challenges over hundreds of millions of years, let us hope that ginkgo remains a living fossil rather than a literal one.

Mark James Thompson

See also Coelacanths; Dinosaurs; Evolution, Organic; Extinction and Evolution; Fossils, Living

Further Readings

Hori, T., Ridge, R. W., Tulecke, W., Del Tredici,

P., Tremouillaux-Guiller, J., & Tobe, H. (Eds.). (1997). Ginkgo biloba—A global treasure. Tokyo: Springer-Verlag.

Sun, W. (1998). Ginkgo biloba. In 2006 IUCN red list of threatened species. Cambridge, UK: IUCN.

Tidwell, W. D. (1998). Common fossil plants of western North America. Washington, DC, and London: Smithsonian Institution Press.

Glaciers Kahlil Gibran
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