Around the Sonoma Plaza at this time of year, near the bear flag memorial, several trees are beginning their farewell to the warmth of summer. They soon will cast thousands of fan-shaped, golden leaves onto the grass, sidewalk and cars below, and among those leaves will be small fruits with an acutely rancid odor. This latter trait has many, no doubt including our hardworking city maintenance crew, wondering why we ever thought to plant these make-work trees in a public park in the first place. This tree has an unusual story, though, and I thought if it were known it might soften our disgust or even help this tree gain some respect.

The ginkgo tree, Ginkgo biloba, also known as the maidenhair tree, is the last species of an entire family of trees that used to flourish around the earth. Two hundred million years ago, California did not exist in any way we would recognize, but the lands that made up the Northern Hemisphere appear to have had the ginkgo and its close relatives in great abundance. At that time, dinosaurs were emerging as the dominant land animals and plants were just beginning an experiment to bear seeds, rather than spores. A whole group of plants, the gymnosperms, or literally, naked seed, including conifers, cycads and ginkgoes, rose to dominate the plant world with this seed-making feature. After millions of years of benign weather, most plants had adapted to warm and moist conditions. The earth then entered into a period of drought and unpredictable weather, and plants with seeds were better able to survive these climate changes. Seed production would be carried into the next major change as well, to the flowering plants that dominate the world of today. The ginkgo was mostly left behind in this advance. As often happens in evolution over long periods, of some fifteen or more species of ginkgo only one now remains.

It is said that ginkgoes still exist in the wild only on remote mountain areas in China. They mature very slowly and for this and other reasons they likely face strong competition from modern plants. It is possible that ginkgoes would have disappeared entirely had it not been for the cultivation practices of Buddhist monks in China in the middle-centuries AD. who planted them around their temples. Ginkgoes were then probably carried to Japan along with Buddhism in the eighth century. The numerous ginkgoes that line city streets around the world today can trace their existence to these relatively few trees.

Ginkgoes have some traits that are worth noting, compared to the more typical flowering trees we are used to. The ginkgo tree is "dioecious", that is, the entire tree is either male or female. The male tree produces grains of pollen which must be carried to a female tree on the wind. When ginkgoes evolved long ago, insects weren't yet helping plants pollinate as they do now, and birds didn't even exist to help.

Because they are so old and until recently very rare, ginkgoes appear to have no natural enemies left. They do well even with pollution. They are one of the few trees that can grow well in an urban area with heavy traffic. For this reason, one might say the automobile has helped to make their comeback possible -- because they are so hardy, they have been planted on city streets around the world.

Possibly linked to this tolerance to stress, ginkgoes are also used as a medicinal plant. While the coating around the seed is better left for compost, the seed itself is edible and is touted by Chinese medicine for its tonic qualities. The leaves are used in now popular herbal supplements as an anti-oxidant, to support human adrenal functions, and to improve circulation, especially for functions of the brain, including memory.

Perhaps this last trait will encourage us to remember the ancient ginkgo as a special tree long into the future.