A little over four years ago I wrote an article about sweet gum trees and the balls they produce. At that time I noted that sweet gums could be found growing all over Rye.
By Bill Lawyer
A little over four years ago I wrote an article about sweet gum trees and the balls they produce. At that time I noted that sweet gums could be found growing all over Rye. I also noted that one reason for this is that the trees do well in acidic soil, which we have in equal abundance.
What more could we learn about the sweet gum trees that hasn’t already been covered?
Plenty as it turns out. I just barely touched the surface, particularly in terms of the trees’ unusual reproductive strategy.
While many species of plants have both the male and female parts on the same flowers, sweet gums have the male and female parts on separate flowers, on different sides of the branches. We’re talking sexual fertilization here — not putting fertilizer on a field or garden to help plants grow.
Sexual fertilization takes place when ripe pollen from a male anther of the same kind of flower catches on the female stigma. Each pollen grain sends out a tiny threadlike tube. The tube grows down through the style and pierces one of the ovules in the ovary.
The way to remember which is which in sweet gums (the trees themselves have no problem doing this) is that the leaves are unfurling as the male flowers (staminates) are clustered in racemes (flowers along a central stalk) above the leaves, while the female (pistillate) flowers are suspended below the leaves.
In addition to being on separate areas of the branches, they look quite different, at that. The female flowers are clustered into small, green balls, where the male flowers are packed with miniscule yellow to orange pollen grains that are blown by the wind by the thousands (even millions) as they separate from the packed racemes.
A grain of sweet gum pollen is tiny — about 30 millionth of a meter in size.
The great majority of all the pollen ends up on the ground, or in many cases along the sides of the streets and sidewalks where the trees grow. I’ve noticed squirrels, birds, and chipmunks feeding on them. In my neighborhood this occurs from late May to mid-June. The City’s street sweepers collect whatever remains.
Nevertheless, enough somehow manages to find its way to the female flowers. When the pollen gets there, the curled, tubular structures covering the surface of the female flowers are their stigmas, whose surface is sticky, enabling them to catch the pollen. And fertilization occurs.
Over the summer the female flowers harden, turn brown, and produce seeds.
According to health reports, sweet gum pollen is only mildly allergenic. But when the piles of pollen that end up on the streets get dried out they can get dusty and result in people sneezing.
On a more positive note, the US Department of Agriculture reports that sweet gum trees have provided resources for humans and wildlife over the years.
Native Americans used the sap of the trees as a chewing gum. They made a tea from the bark of the trees. Medicines were made from all parts of the tree.
As for the seeds and pollen, among the birds that feed on them are goldfinches, purple finches, mallard ducks, bobwhite quails, Carolina chickadees, yellow-bellied sapsuckers, white-throated sparrows, towhees, and Carolina wrens.
And all this can be seen happening, right in our backyards.
