The ginkgo (Ginkgo biloba), or maidenhair tree, is the last surviving member of a group of plants that died out during the Pliocene period about 2 million years ago. The oldest gingko tree fossils are 250 million years old, and the surviving trees are very similar to these ancient Jurassic fossils. The last remaining wild trees are all genetically very similar and may have been planted by humans about 1,000 years ago. The gingko tree's closest living relatives are the cycads, although the name maidenhair tree tree comes from the leaves' superficial similarity to those of the Adiantum maidenhead ferns.
Adult trees can grow up to 160 feet high, with erratic branching and an uneven crown. Young trees are spindly and have a sparse crown, which thickens as they age; the crown may not fully develop until the tree is over 100 years old. Many old trees have multiple trunks. The leaves are up to 6 inches long and fan-shaped or ovobate in shape. They can be split almost into two sections (bifurcated) with notched edges. Female trees produce oval, tan to orange-brown fruit that smells of a mixture of rancid butter and vomit due to a high concentration of butanoic acid. Males trees produce small catkin-like yellow cones that release pollen. The leaves turn yellow in the fall and drop during the winter.
Range and Habitat
Wild or semi-wild gingko trees are found only in the Tianmu Mountains of eastern China, although they are genetically very similar and may be descended from cultivated plants. In nature they grow in acidic, silty soils in forest areas and valleys at an altitude between 2,500 and 4,000 feet above sea level.
The species is thought to be the only surviving link between the primitive gymnosperm plants, such as cycads and pines, and the more advanced flowering plants. The female trees produce unenclosed green ovules the size of cherries; these are fertilized by sperm in pollen released by the male cones and carried by the wind. The ovules then develop into rounded fruit with almond-sized nuts, actually gametophytes, inside. Gingko trees can also reproduce vegetatively, with damaged trees producing roots from lateral branches; these roots can develop into separate clone plants.
The ginkgo tree is best planted in acidic, free-draining soil in full sun, although it will tolerate most types of soil provided it does not become waterlogged. Gingko trees are hardy down to -20 degrees F. The smell and mess created by the slimy female fruit means that most trees planted in parks and gardens are male trees propagated by cuttings, which are then grafted onto seedling rootstock. Propagation by seed is easy, but the sex of the tree will not be known for up to 25 years.
Gingko biloba nuts are a valued food source in China, where they are eaten raw and are an important ingredient in some festive dishes. They are regarded as an aphrodisiac. In Japan, the nuts are an essential ingredient of egg custard, or chawanmushi.
An extract of gingko leaf is widely believed to help the memory and even to slow down the effects of dementia and Alzheimer's disease. A study sponsored by the National Center for Complementary and Alternative Medicine found that gingko supplements produced no increase in memory or cognitive function, although other studies funded by pharmaceutical companies have found positive links.