What Is a Ginkgo? One Species Left From a Group That Once Covered the World

The ginkgo is the only living species in its genus, family, order, class and division, which is a taxonomic isolation matched by very few organisms. Its nearest living relatives are the conifers and the cycads, and the separation from them is ancient. The group appeared in the Permian, diversified through the Jurassic when several genera occurred across both hemispheres, and declined steadily through the Cretaceous and the following period as flowering plants expanded. By a few million years ago it was reduced to a small area of central China, and whether genuinely wild populations survive there is debated, since the trees in the candidate locations may descend from cultivated ones. The species survived the last few thousand years substantially because it was planted at temples and valued, which is an unusual debt for a plant to owe.

The tree carries features that are unusual among living plants:

• •Fan-shaped leaves with veins that fork repeatedly rather than forming a network, which is an ancient arrangement
• •Separate male and female trees, with only the female producing the seeds
• •Seeds with a fleshy outer coat that smells strongly unpleasant when it decays, which is why male trees are planted in streets
• •Motile sperm, which swim, a feature shared with cycads and ferns and lost in conifers and flowering plants
• •Exceptional tolerance of pollution, poor soil, pests and disease, which is why the tree thrives in cities
• •Extreme longevity, with individuals over a thousand years old and no clear sign of ageing in the usual sense

Fossil leaves are common in rocks from the Jurassic onward and are among the more satisfying plant fossils to find, since the shape is immediately recognisable and essentially unchanged. That constancy is what led to the tree being described as a living fossil, a phrase coined by Darwin and applied here among the first cases. The label is useful and imprecise, since the living species is not identical to any fossil one and the lineage has continued to change, though far more slowly than most. What the fossils do establish is the former range, which covered both hemispheres and included high latitudes, with abundant remains from sites now in the Arctic that were forested when the climate was warmer. The leaves are also used to reconstruct ancient atmospheric carbon dioxide, since the density of pores on the leaf surface responds to it and the relationship can be calibrated against the living tree.

The tree has a substantial cultural and commercial presence that has nothing to do with its antiquity. The seeds are eaten in East Asian cooking, prepared after removing the unpleasant outer coat, and appear in particular dishes rather than as everyday food, with a caution attached since eating large quantities is genuinely harmful. Leaf extracts are among the most widely sold herbal products in the world, marketed for memory and circulation, and the clinical evidence is weak, with large well-conducted trials finding no effect on cognitive decline. The tree is planted enormously as street and park planting worldwide because of its tolerance for poor conditions, with male trees selected to avoid the seeds. Timber use is minimal. The economic footprint therefore rests mainly on street planting and on a supplement market that the evidence does not support.

Six trees in Hiroshima within a couple of kilometres of the 1945 detonation survived, resprouted from the base and are still alive, which has given the species a particular significance in Japan and has attached a set of associations to it that have nothing to do with botany. Seeds and saplings from those trees have been distributed internationally as a peace symbol. The survival is not miraculous in any technical sense, since the trees were sheltered, since the species regenerates readily from the base after damage, and since other plants in the area also recovered, and it is a striking illustration of the resilience that the fossil record independently suggests. The wider point is that a species can persist through conditions that eliminate most of its competitors without that resilience being enough to prevent long decline, which is the ginkgo's actual history.

The only living species in its genus, family, order, class and division, with forking leaf veins, separate sexes, swimming sperm and remarkable tolerance of pollution. Fossil leaves from the Jurassic are essentially identical and record a former range covering both hemispheres. It reached the present mainly because it was cultivated at temples after wild populations had nearly gone.