Carol McPherson, North Carolina State Extension Master Gardener
I’m a North Carolina State Extension Master Gardener Intern Volunteer from Orange County, North Carolina. When I moved to Hillsborough five years ago, I went to the local nursery to buy a ginkgo tree, which I’d always longed to have. The saleswoman talked me out of it, saying that they were very slow-growing and pointing out the sparseness of the branches on the young trees in stock. How I wish now that I hadn’t been so easily dissuaded for there is literally no tree on earth with the history and characteristics of the gingko tree.
The word ginkgo comes from the Chinese word ‘xinying’ meaning silver apricot. This refers to the fruit of the female tree, not technically a ‘fruit’ in the botanical sense, by the way, but I’ll use that word today. It’s also called the maidenhair tree because its leaves are similar in shape to those of maidenhair ferns. Less flattering names are the ‘stinkbomb’ tree and adjectives such as “disgusting,” and “repulsive,” are used. But more about that later.
In the botanical world, there are only five living groups of seed plants, and ginkgo is one of them. And ginkgo is the only one that consists of only one species. It is utterly unique, not very obviously related to any living plant, but actually more similar to pines than to maples or oaks. Technically, the ginkgo is a gymnosperm, which means that that the seeds are naked—i.e., they are not enclosed within an ovary. Gymnosperm seeds generally develop on the surface of a scale or leaf, or they are modified to form cones. In the ginkgo, they develop on short stalks, each supporting a pair of tiny green orbs called ovules.
The Thrilling Reproductive Cycle of Ginkgoes
It is the reproductive cycle of ginkgo trees that is especially thrilling. Think about a tree being fertilized by swimming sperm… now how unusual is THAT?
I’m going to borrow some descriptions here from Nancy Ross Hugo, author of Seeing Trees. She describes how each of the two tiny ovules secretes a droplet of sticky fluid that sits on the surface, grabs the pollen as it floats by on the breeze, and brings it into the female cells. Nothing happens for a couple of months—the pollen is carefully stored within the female tissue. When the time for fertilization arrives, the ovules grow a pollen chamber and fill it with fluid. The pollen grain then extends a tube into that chamber and releases two swimming sperm cells (complete with 1000 flagella) into the fluid. The sperm cells swim toward the narrow entrance to the egg cells, and may the best man win—only one makes its way through the portal, where it fuses with the egg and fertilizes it. The author notes that you can actually see a YouTube video of this primordial pulsing of the ginkgo sperm in the pollen chamber. I was able to find it quite easily online and you could clearly see the whirlpools created by the swimming sperm. Among woody trees, only the tropical, ancient cycads are fertilized by swimming sperm. Interestingly enough, this fertilization miracle may also occur within unripe fruit that has fallen to the ground, so don’t be too quick to kick aside any fruits littering the sidewalk.
Speaking of ginkgo fruits littering the sidewalk, now we come to the origin of the ginkgo’s nickname, the stinkbomb tree. When the female fruits begin to decay, they are remarkably stinky. Some people compare the smell to rancid butter, but the fruits contain large amounts of butyric acid, which is the primary unpleasant odor of vomit. Virtually no animal today eats the rotting fruit, but it is likely that in the Jurassic period, carrion-eating dinosaurs probably helped to distribute the seeds. Because of the unpleasant odor, most nurseries will only sell and plant male trees. But that, too, has some disadvantages. The pollen from male gingko trees is highly allergenic, rating a 7 out of 10 on the allergy rating scale. Female trees do not produce pollen. Also, planting only male trees means that all the trees are cloned, thus reducing the genetic diversity that keeps a species healthy and resilient.
Ginkgoes can grow to be quite large, normally reaching an adult height of (65–100 feet). The tree has an angular crown
and long, somewhat erratic branches. The leaves are unmistakable—they are shaped like a fan and somewhat leathery. Even the vein structure in the leaves is unlike any other tree. Two parallel veins enter each blade from the point of attachment of the long leafstalk and fork repeatedly in two toward the leaf edges. Most leaves are divided into two lobes by a central notch, thus the name “biloba”. The autumn foliage of gingkos can take your breath away. In mid-October an entire tree will go from green to gold in a day or two. And again, in mid-November, the tree will drop all its leaves in a single day! I’ve read that if there has been a frost the night before the leaves fall, you can hear them tinkle as they land on each other below the tree.
Ginkgoes are surprisingly hardy. They are often planted in cities, where they don’t mind having their roots compacted under sidewalks, and where they shrug off air pollution as though it doesn’t exist. After all, they evolved during a tumultuous time for our planet, and they had to learn to thrive despite the sooty, sulphurous air of erupting volcanoes. Ginkgoes are also remarkably insect-resistant. In fact, there is almost no insect that even eat ginkgo leaves. Again, these trees evolved long before today’s leaf-eating insects were around. Ginkgoes are also resistant to temperature extremes and to wind.
So as I describe the wonders of this dinosaur-distributed, volcanic air-breathing, swimming sperm fertilized, living fossil (the gingko), I again kick myself for not purchasing that ginkgo tree five years ago. Yes, it was scrawny, but it would be five years older and five years bigger today. The tree is a wonder of nature, the only living bridge between the prehistoric plants of the ancient past and our modern plants of today. I do wish I had one of my own.
We end with a portion of a poem from Howard Nemerov, called The Consent. It was published in a book called The Western Approaches published in 1975.
Late in November, on a single night
Not even near to freezing, the ginkgo trees
That stand along the walk drop all their leaves
In one consent, and neither to rain nor to wind
But as though to time alone: the golden and green
Leaves litter the lawn today, that yesterday
Had spread aloft their fluttering fans of light.
This is Carol McPherson and this is Tree Talk.
Carol McPherson, NC State Extension Master Gardener Intern in Orange County, NC
Tags: arbor day, ginkgo, trees