The Sunny Chemistry of Marsh Marigolds

Cold mist pelted my face as I biked along the narrow shoulder of the county highway. Earlier in the morning I had been overly optimistic about the forecast and the weather radar, with the end result of me bike commuting in the rain. The chill seeped inward, and my thoughts followed, so that soon I was grumbling wordlessly in my head about the soggy, gray weather.

One look upward was all it took to brighten my mood—something golden was shining through the misty swamp. No, not the sun—it was a huge patch of marsh marigolds! With large, vivid green leaves, and yellow, cup-shaped flowers, these members of the buttercup family provide lovely patches of color even in soggy wetlands. Their scientific name, Caltha palustris, means “goblet of the marsh” Suddenly, riding my bike in rain became a lot more pleasant.

While the showy flowers may beckon you to take some home, all buttercups can cause irritation and blistering of the skin if handled. Swallowing any part of the plant can cause intense burning of the mouth and digestive tract, followed by nausea and convulsions. All mammals, not just humans, seem to be affected. Luckily, a bitter taste warns of the inedibility of this common plant, and lethal poisonings are rare.

The culprit for these nasty reactions is a chemical called ranunculin, named for the Ranunculaceae family in which is it found. Ranunculin is both an “antifeedant” (a chemical agent that causes a pest to stop eating), and an insecticide. In one study, worker ants who encountered ranunculin showed a 19% increase in their mortality rate, and the authors suggested further research into the chemical for commercial pest control.

So how does a plant even begin to make a toxin like this? I’m not a chemist, but from piecing together information in a Wikipedia and Google Scholar treasure hunt, this is my explanation: The marsh marigold manufactures glucose, a type of sugar, during photosynthesis. Then, another small organic molecule is bound to the glucose, creating the glycoside called ranunculin.

Many plants store chemicals in the form of inactive glycosides like this. Glycosides are activated when enzymes break off the sugar molecule, making the other chemical available for use. In the case of ranunculin, it breaks down into protoanemonin, which is the glycoside chemical that causes the skin and bowel irritation associated with marsh marigold.

Plant glycosides are often used as medications, and marsh marigold has a long list of traditional medicinal uses. Do you need to remove a wart? Cure a cold? Ease the symptoms of anemia, convulsions, or coughing? Marsh marigold has been used to treat all of those, although there is little modern medical evidence to support its use.

With further exposure to air and water, the skin irritant protoanemonin is changed to the more benign chemical anemonin, which German scientists have found to have antispasmodic and analgesic properties. It, and not protoanemonin, may be responsible for the medicinal properties of marsh marigold. Or maybe they work together. Both medicine and nature are complicated.

This beautiful spring flower is also listed as an edible, with many cautions. Leaves and tightly closed buds must be boiled in a few changes of water, and while the leaves can then be eaten like spinach, the buds still need to be pickled for a month to be safe. All of these techniques probably help to change the toxic protoanemonin into the less hazardous anemonin. Still, I don’t think I’d mess with it.

It’s hard to imagine all of what goes on at a chemical level in nature. Here is a common plant, growing in mucky wetlands, that uses carbon, hydrogen, oxygen, and energy from the sun to make food, chemical weapons, and pharmaceuticals.

And the amazing talents of marsh marigolds go even further. Even a glimpse of their sunny blossoms brings a smile to my face, causing the release of endorphins and serotonin in my brain, and the end of my dreary wet grumblings. How wonderful is the chemistry of nature!

Author’s Note: This article was originally published in 2013. 

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

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