Ginkgo Biloba - A Living Fossil

The Ginkgo tree really catches our interest. It is truly a living fossil, essentially unchanged for millions of years. It once grew wild over much of the earth, including Greenland. It is first found in fossils from the Triassic period. In the Jurassic and on into the Tertiary, the ginkgo was abundant all along the Pacific coast of North America. But then it seemngly disappeared.

Only recently, about 300 years ago, did the European world learn about this tree. British travellers had found small groves of the ginkgo growing in a remote valley in China. Amazed, they secretly pocketed some leaves to take home. However, not until the late 19th century did botanists relocate the Chinese source and get permission to collect some seed. They distributed the seeds to reputable botanic gardens in many countries in the northern hemisphere. Their efforts to grow the Ginkgo were successful. Now we have a tree that is probably the only species of its kind and that probably has been in existence unchanged longer than any other.

Today the Ginkgo is a sacred plant around Asian temples and is widely grown as an ornamental in northern countries. It is unaffected by insects and can endure the poisonous pollution of the modern metropolis. It is a smooth, sparingly branched tree, up to 120 feet [37 m] high. Its deciduous fan-shaped leaves resemble maidenhair fern leaflets.

Botanically it provides an interesting exercise in tracing the development of plant life through the periods of evolution. In it, we see the evolutionary change from cycads and later into conifers. The main stem of the ginkgo, when seen in cross section, has the cellular construction of a conifer, while the lateral dwarf branches which bear the leaves, flowers and nuts, are similar to the cycad, being pithy in the centre.

Being dioecious, the pollen and seed ovules are on separate trees. One tree bears the ovules while the male sporangium come from a small cone on another tree. The male spores are carried by the wind to the sticky ovule. It is an inefficient fertilizing method but some seeds or nuts develop. These are small, smooth and whitish, called in some areas "silver almonds". In China and Japan, the seed coat is roasted off and the inner nut much enjoyed. In Taiwan, food vendors sell them on the street.

However, when the nuts are left on the ground after they fall, the outer case forms a mushy, foul smelling blob. To avoid this, arborists prefer to plant the androgynous tree. As well, arborists have worked on Ginkgo biloba and we can now buy the male trees in slender forms that are more compatible with city streets.

Editor's Note: The OHS is looking for a suitable location to plant a small grove of ginkgos as a Millennium project. For examples of these trees in the Ottawa area, visit the Arboretum at the Central Experimental Farm.

Please contact the OHS or the author if you wish to republish these articles. © Ottawa Horticultural Society

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