Take The Quiz: How Well Do You Know Your Asters?

Aster Frikartii Monch

One of the many things I love about late summer are the throngs of colorful, star-shaped blooms that populate the landscape. The flowers congregate along roadsides, drift lazily across meadows and form neat combinations by houses and in town squares. Most of us are well acquainted with the yellow ones (sunflowers), but less aware that the brood also comes in shades of red, pink, purple and white. The flowers are all part of the Aster family (Asteraceae), the largest and most diverse group in the plant kingdom.

The scoop on the Aster Family

You may have noticed some of the flowers’ shared characteristics; many feature a round central disk surrounded by colorful petal rays. The Aster family is exceedingly large and numbers in the tens of thousands. According to The Plant List, there are currently 1,765 genera of flowering plants and over 27,000 known species growing in diverse climates all over the world.

Gaillardia or Indian Blanket Flower

The botanical name Asteraceae comes from the Greek ἀστήρ meaning star, a reference to the star-like shape of the flowers. But some call the family by its common name, Daisy, from the Old English meaning ‘day’s eye’ (a reference to the flowers’ petals that open at dawn.) Still others refer to the Aster family as the Compositae family, since the inflorescence is a composite of many tiny, individual flowers.

What’s special about Asteraceae is that while at first glance they make look like one flower, they are actually composed of many, all inserted on a common flower head. Of these, there are two types of flowers that may occur. Tubular, petal-less florets are found in the center of the flower disk while flat, ray-shaped florets (resembling petals) are found at the perimeter.

Zoom in on the photo and you’ll see the flowerhead is not flat, but actually made up of hundreds of tiny flowers.

Leucanthemum (daisy) displaying both tubular and ray florets

Within the family there are also several variations. Some flowers have only disk florets, others only ray, and then there are members like daisies, coneflowers, common sunflowers and asters that have both disk and rays.

Flower head of Echinops ritro, Globe Thistle, contains no petal florets

Scientists believe the highly specialized flower head, which also contains seeds and nutrients, helps the plants to store energy during periods of drought and possibly also contributes to their longevity. I know in my own experience that once established, my Aster family members like coneflower, daisy and blanket flower do indeed require little water. And certainly the roadside gardens filled with native sunflowers, daisies and asters are living proof of these flowers’ remarkable survival ability.

Of course every family has its outliers, and the Aster family has a few. These include the food crops lettuce, chicory and globe artichokes. Notice the two types of florets on the mountain lettuce below.

Mountain lettuce, Latuca perennis

Perhaps the most difficult members of the Aster Family to tell apart are the yellow ones. Superficially, many of the flowers look alike. But on closer inspection, their disk and ray flowers are all slightly different.

Take the quiz!

Below are some well-known members of the Aster family found blooming in the late summer and fall. Can you identify them? (For answers and a detailed list of these common family members, please see below.)

Answers: (from top) Coreopsis grandiflora, Golden Marguerite, Rudbeckia (Black-Eyed Susan), Helianthus tuberosis (Jerusalem artichoke), Helenium autumnale (Common Sneezeweed), Helianthus annum (Sunflower), Heliopsis helianthoides (Smooth Oxeye), Gaillardia (Indian Blanket Flower), Arnica montana

If you’d like to add some of these beautiful flowers to your garden, or just be able to identify some more members of the family, following is a list of well-known species in the Aster family and their value in the garden.

Ornamentals

Aster, Echinacea (Coneflower), Rudbeckia (Black-Eyed Susan), Cosmos, Daisy, Fleabane, Dahlia, Tickseed (Coreopsis), Liatris, Gaillardia (Blanket Flower), Erigeron (Fleabane), Zinnia, Chrysanthemum, Oxeye daisy, Yarrow

Herbal Teas, Medicines and food

Calendula (Pot marigold), Chamomile (Anthemis), Echinacea, Arnica, Endive, Lettuce, Artemisia

Great Nectar producers

Helianthus annus (Sunflower), Solidago (Goldenrod)

Insecticidal properties

Marigold, Tanacetum, Pulicaria (False Fleabane), Chrysanthemum

Weeds

Dandilion, Ragwort, Ragweed, Sneezeweed

Want to know more? For a detailed list of Asteraceae, its genuses and where Asteraceae fit in the plant kingdom, click here for USDA Natural Resources Conversation Service.

 

Scientists Uncover Why Young Sunflowers Follow The Sun

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A young sunflower

Sunflowers are known for their unique tracking ability. As they grow, young sunflowers follow the sun’s motion from east to west from sunup to sundown. Come nightfall, the flowers pivot from west to east, only to begin the cycle all over again at dawn. Scientists have observed this behavior as far back as 1898. But until now, no one knew how the flowers did it.

Now comes a new study published this week in the journal Science that suggests that young sunflowers, just like people, are guided by circadian rhythms. These internal ‘body clocks’, which help regulate the plant’s growth, are set to respond to environmental cues. And they are the chief mechanism behind the plant’s unique tracking behavior.

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“It’s the first example of a plant’s clock modulating growth in a natural environment, and having real repercussions for the plant,” said Stacey Harmer, professor of plant biology at University of California-Davis, and senior author of the paper reporting the discovery.

And that’s only half the story. It turns out that young sunflowers are not only attuned to the positional changes of the sun, they can even anticipate the seasonal shift between long and short days and adjust their behavior accordingly.

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According to Harmer, scientists uncovered this astonishing fact by using a time-lapse video to observe how the plants moved during different times of the year. They discovered that during long summer days the sunflowers rotated more slowly, but come nightfall, they quickly repositioned themselves to face east before dawn. However, in September when the days grew shorter, the flowers took longer to reorient themselves, indicating that they knew when the sun was coming up.

(Harmer notes that the research applies to young flowers only, which are the only ones that follow this circadian rhythm. Once flowers are mature, or the yellow petals have unfurled, the flowers remain in place.)
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They tricked the plants

To determine what made young sunflowers follow this circadian rhythm, scientists conducted a series of experiments using plants in the field, in pots outdoors and in indoor growth chambers. In the field, they purposely turned potted plants to face west in the morning to disrupt the sunflower’s tracking ability.

Scientists discovered that those plants that were deliberately faced westward still rotated to follow the sun (in reverse), but they grew more slowly than the other sunflowers, eventually developing into smaller plants, with smaller leaves and about 10 % less biomass.

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Young sunflower in the field

In a second series of experiments, the scientists moved potted sunflowers into an indoor growth chamber with a fixed overhead light. For several days, the sunflowers continued their daily rotation which, according to Harmer, is behavior typical of a mechanism driven by an internal clock.

The sunflowers really started tracking “the sun” again when scientists created an artificial 24-hour day by turning adjacent lights on and off in an arc to replicate natural conditions. However, when the scientists stretched the artificial day to 30 hours, the plants could no longer reliably track the artificial sun’s movement.

The flower doesn’t rotate, the stem does

But what is the actual mechanism rotating the sunflower? It turns out that it isn’t the flower at all, but the stem.

By placing ink dots on the stems and filming them with a video camera, scientists found that as the plant turned to follow the sun, the east side of the stem grew more rapidly than the west side. At night the reverse was true; the west side grew more rapidly as the plant swung the other way. They concluded that this rhythmic tracking helped the sunflowers absorb as many photons from the sun as possible, which is essential in creating the organic molecules the sunflowers use as food.

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Once mature, sunflowers stay facing east

Finally, another series of experiments revealed that once the sunflower matures and the flower opens up, it finishes its tracking and remains in an east-facing position. This gives it a distinct advantage.

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In the morning, east-facing flowers heat up more quickly and studies show that given a choice, pollinators spend longer time on individual flowers if they are warm.

Fascinating to think about next time you see a field of sunflowers –