Many trees turn bright yellow in the autumn, but one of my favorites is the bright yellow Ginkgo tree, found in many locations since it is a popular landscaping tree. But this tree is unique in many ways. The trees adopt a very independent attitude to turning. Some trees will be yellow, and semi-bare, while others are still green, and still others exhibit an odd patchwork, with some yellow areas, some green. And the show doesn’t last for very long, because once an individual tree decides to drop, it’s all over in a few days.
The leaves are unique among seed plants, being fan-shaped with veins radiating out into the leaf blade, sometimes bifurcating (splitting) but never forming a network of veins as a maple tree for example.Two veins enter the leaf blade at the base and fork repeatedly in two; this is known as dichotomous venation. Click this photo for a closer look.
The Ginkgo is known as a living fossil, with fossils recognisably related to modern Ginkgo from the Permian, dating back 270 million years. Plant classification is a bit complex, but in evolutionary order, after the mosses and worts (no proper roots or water transport), and ferns, horsetails, and club mosses (proper roots, bear spores), we get the two big divisions, the gymnosperms (‘naked seeds’) and angiosperms (‘covered seeds’). Angiosperms are all the plants that people put in gardens, like cabbages and dahlias. Almost all surviving gymnosperms are conifers – Christmas trees, and so on – but the group also includes cycads (tropical plants rather like palm-trees), and of course the ginkgoes. This plural is a bit odd, since there’s only one species of ginkgo left now, but things were different in the days of the dinosaurs. There were many species then, with a range of leaf shapes.
How did the Ginkgo come to be in your yard? From China it was transplanted to Japan, probably by Buddhist monks in the 1100’s. Englebert Kaempfer, a German botanist, wrote about it after his stay in Nagasaki (1690-1692), and by the 1730s ginkgo seeds had been brought to Holland, and a tree was growing in Utrecht. It could then be propagated by layering (since the seeds take many years to start forming), and so spread across Europe. After the War of Independence it arrived in American in 1784, where it became common.
Ginkgo trees have separate sexes, just like mammals, and only the female (of course) bears fruit, which is a very important thing to know. If you want to plant one in your yard be sure to get a male tree. The female tree bears seeds every other year, and they smell like vomit! Several such trees grew along the sidewalks next to a class building when I was at Ohio State University, and if you stepped on the fallen fruit, your shoes stank for days.
In addition to its use as a delicacy, the ginkgo has been used in traditional Chinese medicine, and is enjoying popularity now in “alternative” health circles. (Perhaps half of the websites about the ginkgo are herbal remedy sites of one sort or another.) Generally infusions from the leaves are used, and these are claimed to improve one’s brain power to an amazing degree. They do contain substances which are known to improve circulation to the brain in particular; rather less believable is the original Chinese theory that the leaves must be good for the brain, because they resemble a section of the brain in shape. Also fascinating: a good number of sites advocating use of ginkgo leaf infusions claim that the seeds are toxic. That’s good enough for me – I won’t eat them!