Weather Lab: Heliotropic flowers chase the summer sun

The blooms move at the pace of the summer days
Updated: Jun. 16, 2021 at 8:35 PM AKDT
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ANCHORAGE, Alaska (KTUU) - The long days of sunshine in Alaska this time of year is like a feast for flowers. As Alaska’s Weather Source continues its Weather Lab Summer Series, this week’s topic is the science behind how flowers move to soak up the long summer days.

Meteorologist Jackie Purcell takes viewers to the Alaska Botanical Garden to show some of the flowers blooming there. There is a type of flower in the garden with a special adaptation that enables it to take advantage of the long daylight hours.

The Alaska Botanical Garden has about eight acres of cultivated gardens, with nature trails leading visitors between the some 1,100 varieties of plants and perennials — plants tough enough to withstand the weather in Southcentral Alaska. One can also see about 150 species of plants native to Alaska in the garden.

The flower of focus is the Arctic poppy. The adaptation is that they are heliotropes, or plants that move in a heliotropic motion. Poppies track the sun’s path across the sky throughout the day. Their petals open up during the first light of day and then they contract them at night.

But what about that word, “heliotropic”? It means “turning or growing toward the light”. It is derived from the Greek word “helio” or “helios”, relating to the sun and “tropic”, meaning “turned toward,” or “with an orientation toward”.

The arctic poppy has cup or parabolic-shaped flowers that move with the sun. The cup helps to focus sunlight on the middle of the flower; this warmth helps it to grow faster and attract insects to the center of its bloom. Tundra plants can grow and flower at lower temperatures than any other plants on Earth. These slow movements can’t be seen by just looking at the flowers — one needs a timelapse video to see the flowers in action. And these flowers use this tracking ability to full advantage because the summer growing season is only 50 to 60 days in the high Arctic.

Sunflowers are also known to track the sun’s movement diurnally, or in a daily cycle.

Heliotropism is now often referred to as phototropism. Another way to describe plants that follow the sun’s path through the sky is “solartropic”. These are cool words that you can look up and enjoy using in casual conversation.

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