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The Debunker: Do Sunflowers Turn to Face the Sun?

by Ken Jennings

Take a break from your fun in the August sun to ask yourself: what do I really know about this giant glowing globe of plasma shining down on my picnic/game of Ultimate Frisbee/clothing-optional beach right now? Given that the Sun is what makes life on Earth possible, it's appalling how much misinformation we've been fed about our nearest star. Speaking of our nearest stars: Ken Jennings, that one guy from Jeopardy!, may not be as bright as the Sun, but he's an expert on debunking myths and misconceptions. All month, he'll be lighting up our stellar misconceptions regarding the sun.

The Debunker: Do Sunflowers Turn to Face the Sun?

In English, it's not really clear whether the sunflower is named for the bloom's resemblance to a traditional yellow-rayed sun, or for its reputation for following the Sun across the daytime sky. In some other languages, however, there's no ambiguity. In French, the sunflower is the tournesol—the "sun-turner." In Spanish and Italian, the translation is the same: girasol or girasole. Besides the fact that it produces seeds that baseball players like to spit, this appears to be the sunflower's great claim to fame: everybody knows that it turns its face during the day to track the Sun's movement.

well how nice

The ability of plants to turn to face the Sun is called heliotropism, and it's not uncommon. The ancient Greeks even concocted a myth about a nymph who so longed for the sun-god Helios that she turned into a flower when she died: the purple heliotrope, whose leaves followed Helios's chariot across the sky. But science has known since 1597 that sunflower blooms, despite their name, are not heliotropic. Everything you know about sunflowers in wrong! (Except for the baseball player thing.)

Here's what actually happens: immature sunflower buds do exhibit heliotropism, moving with the Sun. But once the familiar yellow flower heads appear, the movement stops. The flowers stay in the direction their buds were last pointing, which is typically east, toward the morning sun. This gives fields of sunflowers their uniform direction, and causes the mistaken impression, during much of the day, that sunflowers are actively tracking the Sun. But come back in the evening, when the Sun is in the west, and the sunflowers will still be facing east. Come on, sunflowers. Get with the program..

Quick Quiz: Whose painting Vase with Fifteen Sunflowers sold at auction for a record $39.7 million in 1987, kicking off a new era in big money art sales?

Ken Jennings is the author of six books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at ken-jennings.com or on Twitter as @KenJennings.