I use witch hazel extract on my face every night. It’s derived from the leaves and bark of the common witch hazel plant, Hamamelis virginiana, and in addition to cleaning the skin is supposed to help relieve it of irritation. In light of witch hazel’s calming properties, I guess it’s a little funny that a witch hazel plant starts out, very literally, with a bang.
For a plant to produce offspring and continue that beautiful circle of life that Elton John sang about, it has to send seeds out like children into the big, bad world, a process known as seed dispersal. And just as some parents and caretakers allow their children to keep living at home after graduation, maybe staying in the basement or the pool house, while others practically pack their kids’ boxes and suitcases for them, plants go about seed dispersal in any number of ways:
Letting gravity take its course
Encasing their seeds in tasty fruits for animals to eat so that the seeds will later be, um, deposited (seed dispersal plus, now with a fertilizer bonus)
Attaching lightweight structures that allow the seeds to drift serenely on the breeze
Launching them violently into the surrounding environment
That last option probably sounds made-up. It isn’t. Witch hazel seeds develop inside of a capsule that bursts at maturity. Like a circus daredevil spewed from a cannon, each seed ends up shot about twenty to thirty feet away from the parent plant. The capsule makes a popping sound upon bursting—or a bang, to go back to where we started this.
It’s nothing like the method of seed dispersal that many trees here in the Midwest employ. Wind dispersal seems more appropriate for a plant that’s used to make a soothing extract. The way that whirlybirds or helicopter seeds like the ones seen in the photo above (the technical term for a winged seed like these is a samara, presumably because “whirlybird” never stuck in scientific circles) simply flutter to the ground perhaps offers a greater sense of enchantment than the botanical equivalent of cannon fire. Plus, as mentioned before, all the other plants are doing it: various trees including ashes, the winged elm (naturally), and most conspicuously maples all produce winged seeds.
So why doesn’t the witch hazel plant give in to peer pressure? Well, as helpful as winged seeds are in spreading a plant’s offspring far and wide, that huge range of dispersal (we’re talking hundreds of feet here) comes with certain trade-offs:
Not every seed is guaranteed to land somewhere hospitable and grow, so the parent plant spends a lot of energy producing seeds that will never germinate.
In order to be light enough to dance on the spring breeze, winged seeds aren’t packed with as much nourishment as, say, the seeds packed into fruits are. As a result, some will be too poorly nourished by the time they land to sprout.
Kids like to pick them up and toss them into the air, at least where I grew up, because it looks really neat (see trade-off #1).
No doubt that witch hazel’s exploding seed pod looks (and sounds) neat, too, but the exchange there is that it takes even more energy than making a load of winged seeds to actively expel a few seeds from one’s body. Each plant evolves the method of seed dispersal best suited to its environment. If it happens to delight us with showers of whirlygigs or sudden eruptions of seed pods, well, that’s just one more way we’ve benefited from evolution, I’d say. It’s right up there with opposable thumbs in scientists’ minds, I’m sure.