Vincent van Gogh - Sunflowers - 1889
Vincent van Gogh's Sunflowers (1889)

Most admirers of van Gogh’s iconic “Sunflower” paintings gaze upon the golden inflorescences without any awareness of the scientific conundrum they pose. But researchers from the University of Georgia have finally cracked the case with a paper published in PLoS Genetics.

California buttercup
Buttercup taken at Tilden Park in Berkeley, California by Calibas
Orchid taken by Alex Tievsky SaveThePoint

The puzzle begins with the fact that all flowers are either radially or bilaterally symmetrical. A buttercup is an example of radial symmetry; it looks the same no matter how you rotate it. An orchid, on the other hand, has bilateral symmetry, like a human face–the left and right sides look the same, but you can tell whether it’s right side up or upside down.

Here’s the sneaky thing: a lot of seemingly radially symmetrical flowers are actually clusters of tiny bilaterally symmetrical flowers, or florets. In fact, this is true of one of the biggest flower families, Asteraceae, which includes such familiar friends as dandelions, daisies and, yes, sunflowers.

Then the sunflower makes things extra complicated by building its cluster out of two kinds of florets: bilaterally symmetrical ray florets, and radially symmetrical disk florets. This may sound confusing, but it’s obvious as soon as you look for it: the classic sunflower is a ring of petals (ray florets) surrounding a big disk that will become filled with seeds (fertilized disk florets). The ray florets are infertile–they’re just there to help attract pollinators.

Sunflower (Helianthus annuus)

Now at last we can consider van Gogh, and his double-flowered sunflowers. They’re mutants.

A double-flowered mutant has no true disk florets, only concentric rings of ray florets–a profusion of petals. Consequently, the plant loses a lot of its fertility. You might wonder, can the opposite occur? Indeed, in tubular-rayed mutants ray florets are replaced with radialized, fertile disk florets.

Mark Chapman and his colleagues have just discovered that one particular gene, called HaCYC2c, causes both mutations. If HaCYC2c is over-expressed, it creates double-flowered van Goghs. If the gene’s function is lost, however, you get tubular-rayed flowers.

I particularly love this study because at least the first part of their methods is totally accessible to anyone who’s studied Mendelian crosses in high school biology. See:

Van Gogh's Sunflowers - Figure 2

Okay, maybe it’s a bit tricky. If you want to puzzle it out but you’re rusty on Mendel, here’s a primer.

Of course, you don’t need to understand Mendelian crosses–or the super-sophisticated genetic mapping that Chapman et al. use later–to appreciate van Gogh’s art. Nor do you need to be an Impressionist fan to appreciate sunflower genetics.

But I think we can all appreciate that it’s not often a famous painting is included in Figure 1 of a scientific paper.

Van Gogh's Sunflowers - Figure 1
Figure 1. Entire inflorescences (A, C, E) and individual florets (B, D, F) from wildtype (A, B), double-flowered (C, D) and tubular (E, F) sunflower individuals. Florets are arranged left to right from the inner florets to the outer florets. (G) “Sunflowers (Still Life: Vase with Fifteen Sunflowers)” by Vincent van Gogh (1888) with double-flowered heads pointed out with arrows. Panel G was obtained from Steve Dorrington on flickr (available at and is distributed under the terms of the Creative Commons Attribution 2.0 Generic (CC BY 2.0) License.
Geneticists Solve Van Gogh’s Mutant Sunflowers After 125 Years 17 April,2012Danna Staaf


Danna Staaf

Danna Staaf is a marine biologist, science writer, novelist, artist, and educator. She holds a PhD in Squid Babies from Stanford and a BA in Biology from the College of Creative Studies at the University of California, Santa Barbara. She helped found the outreach program Squids4Kids, illustrated The Game of Science, and blogs at Science 2.0. She lives in San Jose with her husband, daughter, and cats.

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