Plant 103

Ginkgo biloba L. (Ginkgoaceae)



The ginkgo tree is a survivor; it is the only living member of an entire plant division (Ginkgophyta). The tree has survived to the present day in a few isolated pockets of wild forest in China and in cultivation. Ginkgos are popular trees for planting in polluted urban environments; six trees even survived the Hiroshima atom bomb explosion. Once thought to be extinct in the wild, Ginkgo biloba is now known to grow apparently wild in eastern China. Recent genetic evidence suggests these populations were established from only a few trees, perhaps by monks planting sacred groves. Truly wild populations may be more likely found in remote areas of southwest China.

The first Ginkgo-like fossils appeared in the Early Jurassic (175-200 million years ago), and during the Mesozoic Era the genus diversified and spread across the planet. By the Cenozoic (65 million years ago) all but one or two Ginkgo species were extinct. Ginkgo is traditionally included in the group of seed plants called the gymnosperms, although the relationship of the ginkgophytes to other gymnosperms remains unresolved, the focus active research.

Ginkgo biloba became known to westerners in 1690 when the German botanist Engelbert Kaempfer discovered the tree growing in a Japanese temple garden. Unfortunately, Kaempfer appears to have spelled the plant's common name wrongly in his Amoenitates Exoticae (1712). The misspelling was enshrined in the scientific literature when Carolus Linnaeus adopted it as a formal scientific name when he first described the genus in 1771.

Fan-shaped, notched ginkgo leaves, with their bifurcating, dichotomous venation, are unmistakable among the seed-producing plants. A former common name for gingko - maidenhair tree - alludes to superficial leaf similarities with the maidenhair fern. The horticultural value of ginkgo lies in the unusual leaves, which turn a vivid golden yellow in autumn.

Gingko has separate male and female trees. The male trees produce tiny, pollen-producing cones, whilst the female trees, once pollinated and fertilised, produce seeds surrounded by a fleshy, pale yellow, butyric-acid-rich, vomit-scented coat. Consequently, male trees are more commonly planted as street trees than female trees.

Gingko seeds are consumed in east Asia, whilst in the West ginkgo has become something of a medicinal panacea. Diverse pharmaceutical claims have been made for ginkgo extracts that range from the enhancement of cogitative function, through treatment of dementia to treatment of hypertension and altitude sickness. Yet rigorous investigations have found no scientific evidence for these claims.

Further reading

Crane P 2015. Ginkgo: the tree that time forgot. Yale University Press.

Tang CQ al et 2012. Evidence for the persistence of wild Ginkgo biloba (Ginkgoaceae) populations in the Dalou Mountains, southwestern China. American Journal of Botany 99: 1408-1414.

Stephen Harris