Just before Christmas, in ‘More Ginkgos’ I looked at how ginkgos spread and flourished around the world for some 200 million years but eventually ended up restricted to small areas of China when Earth’s climate cooled. So how come they are now such widespread ornamental trees in the UK?
Gingkos in Bute Park, Cardiff, which has Ginkgo leaves as its symbol
When people first arrived in the parts of China where ginkgos survived, some 50 000 years ago, Ginkgo seeds became a source of food – mature female trees produce them in huge quantities. Once the outer fleshy coat is removed, the seed inside is rich in starch and protein. Traditionally, the seeds are buried after harvest to encourage the fleshy tissue around the edible seed to decay – this is the part which smells of butyric acid, remember (see ‘Ginkgo – A Living Fossil’). Later, Ginkgo trees acquired symbolic meaning in several eastern religions, particularly Buddhism, where they symbolised vitality, longevity and resilience – all properties which Gingko clearly has in spades. Both leaves and fruit were soon identified as having medicinal properties perhaps by monks who, like their western counterparts, were amongst the earliest practitioners of herbal medicine.
For at least a thousand years Ginkgo seeds have been used in traditional Chinese medicine, for a wide range of ailments, including lung and respiratory conditions. However the fleshy seed coat also contains three novel allergenic chemicals which produce very nasty allergic skin reactions and the seed itself contains a toxin known as MPN, which interferes with the body’s ability to absorb Vitamin B6; great care must be taken when preparing treatments. In the west, we have focussed on the medicinal properties of flavonoid-rich Ginkgo leaves instead; particularly their putative effects on circulatory problems, memory and concentration. Standardised leaf extracts are widely prescribed in France and Germany though Ginkgo is regarded with more scepticism by the medical profession in the UK, who feel that more research is needed to prove its efficacy.
By the early 18th century, ginkgos were widespread around temples in China and Japan and fifty or so years later they were found in botanical gardens and private estates throughout Europe, brought first to ‘The Low Countries’ because of links between the Dutch and Japan. Two trees, one in Belgium and one in the old botanic garden in Utrecht compete for the title of ‘oldest Ginkgo in Europe’ and are believed to be nearly 300 years old. The famous ‘Old Lion’ Ginkgo at Kew gardens in London is just a little younger. A male tree, it first produced pollen cones in 1795 and is thought to have been the first in Europe to do so.
Kew ‘Old Lion’ Ginkgo biloba (http://www.kew.org/discover/blogs/arboretum/kews-old-lions-celebrate-250-years
Female trees take longer to reach maturity and, of course, won’t produce viable seed unless there is a male tree nearby. Cuttings from the first female tree identified in Geneva were grafted onto male trees in other parts of Europe and eventually viable seeds were produced on a Ginkgo in Montpellier Botanic Garden in 1835.
Late in the 18th Century cultivated ginkgos spread from Europe to the New World – they now thrive in most temperate regions of the globe, though they have only rarely become naturalised. At lower latitudes ginkgos are generally restricted to higher altitudes because they need a cold spell (known as vernalisation) to synchronise the bursting of buds and flowering in spring. Gingko shares this requirement with many fruit trees – it was always a disappointment to us, when we lived in Nigeria, that apples would not grow in the fairly temperate climate of Jos plateau because of the lack of a cold period.
Because ginkgos have been of so much interest to horticulturalists over the last two hundred years, mutations producing novel features have been pounced on and spread, using cuttings or by grafting. There are more than 220 horticultural cultivars today, distinguished by their growth habit, leaves or nuts, all derived from a very restricted amount of genetic material imported from wild Chinese populations – an interesting example of accidentally widening the gene pool to an extent which conservationists usually have to struggle for! It means there is a Ginkgo for every situation – tall, slender varieties for narrow spaces and more statuesque ones of various shapes for specimen trees. This adaptability, together with a resilience which belies their fragile-looking beauty, has made ginkgos one of the most widely-planted street trees in the world (Crane, 2013). Benefits of urban trees range from practical ones such as reduction in flooding and the provision of shade to the aesthetic and psychological though, in the case of ginkgos, not everyone is happy about a female tree in their neighbourhood – it’s back to those smelly seeds again!
The tenacity which has allowed ginkgos to survive for 250 million years serves them well in their role as street trees – they survived the atomic bomb in Hiroshima, after all. The trees can be easily propagated from cuttings, which makes it relatively easy to ensure a supply of male plants, and will regrow if their main trunk is broken. The oldest trees reproduce themselves vegetatively by producing stalactite-like downward growing branches (chi-chis) which root where small embedded buds touch the ground – rather like brambles!
Bramble reproducing vegetatively – roots are growing where the shoot has touched the ground
However the real reason ginkgos have been so successful in redistributing themselves around the globe is surely as much as anything to do with their extraordinary charisma – maybe the only plant to give the so called ‘charismatic megafauna’ a run for their money! How many other leaves are so instantly recognisable?
Crane P.R. (2013) Ginkgo. The tree that time forgot. Yale University Press.