Natural Connections: Cotton, Not Cottonwood

The green fruits on this aspen catkin have split open to release their tiny seeds—each surrounded by a tuft of fluff that will carry it away on the breeze.

Natural Connections: Cotton, Not Cottonwood

Just back from a hike and eager to see what my camera recorded, I plugged my memory card into the computer. I thought I’d captured nodding trillium in just the right light, and I knew my photos of columbine were well-framed between two trees. I’d done my best to focus on a tiny spider hiding among the bright, pollen-filled anthers of a white trillium.

But zooming in on these photos, I noticed something wrong: each of these flowers was fuzzy. No, it wasn’t a faulty autofocus, the images were pretty sharp. It’s just that the flowers were truly covered in fuzz.

The columbine flowers—with their five red nectar spurs pointing skyward on delicately arching stems—were the worst. Was that dryer lint in the woods? And then I remembered: the small rock outcrop where they grew was surrounded by aspen trees. The path had been littered with aspen catkins erupting in white fuzz. My fingertips had a memory, too, of the sticky feeling of columbine stems—the perfect tackiness for capturing fuzz.

Off the cuff, many folks would tell you that the white fluff flying on the breeze this time of year is from cottonwood. The thing is, Eastern cottonwood—Populus deltoides—is pretty rare in the northern third of Wisconsin. But, as it turns out, the white fuzz is a family trait, and local relatives abound.

Cottonwoods are in the willow family, along with aspens and poplars. And, as is typical in plant families, their flowers are all very similar. Although tiny and lacking pretty petals, the flowers cluster together on long, drooping catkins that emerge before the trees’ leaves. With a lovely yellow-green hue, they provide us with some of the first colors of spring.

The flowers’ early emergence is necessary, because they are pollinated by the wind. Spring breezes filter through bare twigs to pick up pollen from catkins on a male tree and deposit it on the catkins of a female tree. Yes, individual trees are one sex or the other, a trait that botanists call dioecious, which means “two houses.”

Catkins of male flowers simply drop to the ground once they’ve sent their pollen on its way. After they are pollinated, the female flowers develop into small, green fruits that are all lined up on the catkin like a braid of chili peppers

Once the seeds are ripe, the capsules split open and curl back adorably—like elf shoes. Out pour tiny seeds, each surrounded by a halo of cottony fuzz. While many allergy sufferers grumble during this phase, the fluff is not the cause of allergies—the pollen that fertilized those seeds was the problem.

Between their small size and mini-parachutes, aspen seeds drift easily on the wind. Their window for world travel is brief, though, since the seeds only remain viable for a short time. Some seeds, like oaks and cherries, fortify themselves for a long wait, banking on patience to help them win the reproduction game. Willow family seeds play a different game—investing a minimum of energy but producing gobs of seeds. Most seeds succumb to desiccation, or fail to land on suitable soil for germination.

If all of the seeds seem to land on your lawn, creating an annoying carpet of natural lint, there’s a fun way to get rid of them. I recently saw a video of a park in Spain (Populus trees grow worldwide!) where someone had set fire to the cotton! Like a mini version of a prescribed prairie fire, the dry cotton burned quickly and left the lush green grass untouched.

Seeds that do win the jackpot of soil moisture, temperature, and sunlight germinate rapidly and begin the race to grow. This is one reason aspens are pioneer species. When a site has been disturbed by a forest fire, flood, or landslide, seeds can float in and grow quickly in the abundant sunshine. Once established, aspens spread by sending new clones up from their roots.

Since many groves are made up of clones of the same individual, a large area may be entirely male or entirely female. Male trees don’t make seeds, and therefore don’t make cotton, either. The forest around my fuzzy columbine flower was female.

If you find yourself irritated by all the cotton drifting around, take a moment to appreciate that across the Northern Hemisphere, dozens of species of cottonwoods, aspens, and poplars are sending their tiny seeds out onto the breeze. And everywhere they land, people just like you are grumbling about the mess.

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.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Growing Up WILD exhibit. Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Last Update: Jun 15, 2022 1:37 pm CDT

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