Each year, in mid-November, a 200-million-year-old ritual is re-enacted all over campus, not by students but by trees. Known for their fluttering fan-shaped leaves, the ginkgo trees that are common in cities and plentiful at the University of Chicago, undergo a breathtaking transformation. Their leaves turn from lime green to lemon yellow and they produce bright orange seeds.
The seeds, often described as “pungent,” fall to the ground, where they get trampled. Then, they get even. They emit a fragrance. The key component of that scent is butyric acid, a short-chain fatty acid that is abundant in the flesh that surrounds the seeds.
It has a familiar smell. Butyric acid is the core scent of rancid butter, the central distinctive smell of human vomit. The flesh also can trigger an allergic rash, similar to poison ivy.
The seeds contain a toxin. Eating more than 10 roasted seeds per day, over time, can cause difficulty breathing, weak pulse, seizures,” according to the National Library of Medicine. Eating fresh ginkgo seeds “could cause seizures and death.”
Nevertheless, people eat them.
“It’s very delicious,” according to Chun-Su Yuan, PhD, the Cyrus Tang Professor in the Department of Anesthesia & Critical Care and director of the Tang Center for Herbal Medicine Research at the University of Chicago.
Those who consume ginkgo seeds let the flesh rot off, pop open the shell and remove the inner nut. They bake, boil or roast it, which reduces, but does not completely eliminate, the toxin. They eat it with rice or add it sparingly to soups and stews.
The seeds are often compared to chestnuts. It “has a particular flavor,” Yuan said, “a little bit bitter, a little sticky, like a soft nut. The texture is nice. It is good food, but do not consume very many pieces, no more than 10.”
Only female ginkgo trees produce seeds. To avoid the smelly droppings, urban planners, landscapers and homeowners tend to plant males. Until a few decades ago, there was no reliable way to tell the difference, but now botanists know how and most nurseries sell only male trees.
The trees get the last laugh, however. They can change their sex, flipping on a whim from male to female.
Ginkgo trees are hardy. They are resistant to diseases, pollution and “pretty much everything else,” according to a 2014 Wall Street Journal article. Some ginkos in Hiroshima, growing near the center of the atomic-bomb blast in 1945, survived. They blossomed the next year. Ginkgo trees can live a long time. There are huge gingkos in China that have survived more than five centuries.
This may be why they are associated with long life. In East Asia, the seeds are considered health food and valuable sources, in low doses, of nutrients. In the United States—where ginkgo extracts, marketed simply as Ginkgo biloba, are the third most common herbal supplement, a billion-dollar industry—they tend to be made from leaves.
An estimated 4 percent of Americans now take Ginkgo biloba tablets. “It is taken to prevent dementia, especially Alzheimer’s disease,” Yuan said. “It is considered an antioxidant, and it does seem to reduce clotting. But it can cause excess bleeding,” he added. “Maybe it could improve brain function by improving blood flow in patients with clotting problems, but we have not yet seen documented benefits in a large controlled trial.”
There was at least one randomized, double-blind, placebo-controlled clinical trial. Investigators from six U.S. academic centers enrolled more than 3,000 participants age 72 to 96 years and followed them from 2000 to 2008. They published their results in JAMA in 2009.
They showed that the standard dose—120 mg twice daily—produced “no evidence for an effect of G biloba on global cognitive change and no evidence of effect on specific cognitive domains of memory, visual-spatial construction, language, attention and psychomotor speed, and executive functions.”
Ginkgo trees, which date back to the days of dinosaurs, have one confirmed neat trick, however. While the leaves of more modern trees—maples, oaks, chestnuts, beeches, poplars, dogwoods, sycamores, pick your favorite—turn dry and brown then fall off over a period of weeks, the ancient ginkgo, which has no surviving close relative, drops its still-yellow leaves all at once, over a few hours. American poet Howard Nemerov honored this quirk with a sonnet, “The Consent.” Here’s a one-sentence sample.
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.