I don’t know about you, but twice a year, Day Light Savings always messes me up. For at least a week after we fall back or spring forward, I’m a wreck—I can’t focus, I’m more tired than usual.
Part of the problem is because that 1 measly hour change messes with the human body’s circadian rhythm. You may have heard of that term before, in Latin circadian roughly translates to “about day”, meaning this rhythm is about ~24hrs long.
Although we still don’t understand all of the details of circadian rhythms, here are some things we do know:
Circadian rhythm in plants:
The most visible way that plants demonstrate their circadian rhythm is by tracking the sun with their leaves or flowers. In fact, the first time this motion appeared in scientific reports was in the 1700s, so we’ve know about it for a while. Even today, we don’t understand exactly how plants control their circadian rhythm.
Sunflowers are excellent for observing this solar tracking. What’s absolutely wild about these flowers is that they reset themselves at night. They follow the sun from east to west during the day, but overnight they reset back to face east for the next sunrise. This demonstrates that, although they may follow the environmental cue of sunlight, that’s not the only driver. Without sunlight at night, they still somehow move back to face east (not south or north) and they are reset back to east before the sun rises again. Check out this video to watch sunflowers in action: https://www.nature.com/news/video-sunflowers-move-to-internal-rhythm-1.15548
Circadian rhythm in orchids:
The most obvious example of circadian rhythm in orchids that I’ve observed in my own plants is flower scent. Have you ever bought a plant that the grower swore smelled beautiful, but every time you smell it, there’s no scent? Try smelling that flower at different times of the day—including the middle of the night. The chemicals responsible for the scent are expensive for the orchid to make. Most orchids won’t waste the energy or resources to make those chemicals if their pollinator isn’t active. It’s like calling your night-owl friend at 6am. Why bother when you know she’ll be asleep and won’t answer? You have a better chance of her answering if you wait for a time when you know she’ll be awake.
For instance, I have an oncidium that only has a scent in early afternoon while my mom has a brassolaeliocattleya (Blc.) that has the most beautiful, powerful scent…at 2am. The difference is that my oncidium’s target pollinator is probably most active in the middle of the day, while the Blc.’s pollinator is likely nocturnal.
Jen Schmidt is a PhD graduate from Cornell University who, with the help of her mother (Barb), is turning into a crazy plant lady at a young age.