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Wednesday, August 10, 2016

Young Sunflowers Follow the Sun, Mature Sunflowers Face East for the Warmth and Bugs (Florida Anyone?)

      Young sunflowers, as you may have observed, are heliotropic and appear to follow the sun (cue The Beatles!). However, mature sunflowers continue to face east once the stalk has matured to gather maximum warmth and pollinators (cue the Beetles!).

       Young sunflowers (Helianthus annuus) grow better when they track the sun’s daily motion from east to west across the sky. An internal clock helps control the behavior, Dr. Stacey Harmer and researchers report in 8/5/16 issue of Science.

      Depending on the time of day, certain growth genes appear to be activated to different degrees on opposing sides of young sunflowers’ stems. The east side of their stems grow faster during the day, causing the stems to gradually bend from east to west. The west side grows faster at night, reorienting the plants to prepare them for the next morning. “At dawn, they’re already facing east again,” says Harmer, University of California, Davis. The behavior helped sunflowers grow bigger.

     Young plants continued to grow from east to west each day even when their light source didn’t move. So Harmer and her colleagues concluded that the behavior was influenced by an internal clock like the one that controls human sleep/wake cycles, instead of being solely in response to available light. 

     That’s probably advantageous, Harmer says, “because you have a system that’s set up to run even if the environment changes transiently.” A cloudy morning doesn’t stop the plants from tracking the sun, for instance.

     Contrary to popular belief, mature sunflowers don’t track the sun — they perpetually face east. That’s probably because their stems have stopped growing. But Harmer and her colleagues found an advantage for the fixed orientation, too: Eastern-facing heads get warmer in the sun than westward-facing ones and attract more insects.

       I was happy to find a sunny topic for this week's PEOTS. This one is for Zoë.  



  1. Surprised that it took this long to work this out. On the other hand, why is East, and not South (in the northern hemisphere) ths best orientation for catching the sun? Aren't fixed solar panels usually aimed south?

    1. I was, too. That's a good question. Maybe because solar panels work year-round to take advantage of winter sun, especially, whereas sunflowers grow mostly in the summer?

  2. Replies
    1. Delightful. Great music, too.

    2. I dunno, jan. They look to me like spectators watching a super-slo-mo replay of an Olympian table-tennis rally between puzzle-god Will Shortz and...well, God, who paddle the golden ping-pong ball to and fro across the firmament of time-space.


    3. Enjoying the back and forth here. . .

  3. Replies
    1. This comment has been removed by the author.

    2. Speaking of Zoetropes, Steph, I learned from PEOTS this week that sunflowers are not-so-much heliotropic. Zoetropic describes jan's time-lapse sunflower link. So, Steph, was your day-by-day-by-day perception of witnessing Zoe grow from infant to young adult in any way Zoetropic?


    3. Lego, it Zoëtropic ! All those still photos of her as a baby, toddler, elementary school kid, tween, teen, and young adult fly by so quickly as the Zoëtrope spins. Life's just one big Zoëtrope, eh?

    4. Umlaut! I’m loutish!


    5. ::::::::::::::::::::::::::::

  4. Replies
    1. Wow, 150 years to reproduce! Amazing to think there are sharks swimming around that may be up to 500 years old. Thanks for the share.

  5. And, since we've been talking about plants, NASA-recommended houseplants. Bamboo is on the list!

  6. New post on "From Fish Fin Rays to Fingers: The Digit-al Age" is now up.