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.

Figure: The ginkgo tree is one of the best-known examples of a living fossil. This ancient tree represents a primitive family of trees common 160 million years ago in China. The ginkgo thrives in well-drained, loamy soil and is particularly resistant to modern pollutants, wind, pests, and disease

Source: Michael Pettigrew/iStockphoto.

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 [Page 591]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 evolvedapproximately 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 fla-vonoids, 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.

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