The word “sunflower” brings to mind a mane of vibrant yellow petals encircling a dark whorl of seeds. But not all sunflowers are alike. Some sunflowers have scraggly petals, for instance, or small centers. Many of the sunflowers Vincent van Gogh depicted in his famous series of oil paintings look rather unusual—they sport woolly, chrysanthemumlike blooms. Now scientists have pinpointed the genetic mutation responsible for these strange sunflowers’ abundance of small yellow petals.

Van Gogh’s paintings from the late 1880s clearly feature some typical sunflowers, but they are paired with what look like fuzzy pom-poms stuck on sunflower stems. Such double-flowered sunflowers, as they are known, have overlapping rows of supple yellow petals and a small, sometimes hidden, center. In a new study, John Burke of the University of Georgia and his co-workers traced the unusual floral arrangement of van Gogh’s sunflowers to mutations of a single critical gene. The findings appear in the March 29 PLoS Genetics.

Burke and his colleagues worked with typical sunflowers as well as double-flowered cultivars, such as the teddy bear sunflower, which looks like a giant dandelion. By crossing different varieties of sunflowers with one another and crossing their offspring with themselves, the researchers discovered that double-flowered cultivars have mutated forms of a gene called HaCYC2c.

For thousands of years people have been growing sunflowers for their seeds, oil and beauty. The first double-flowered sunflowers probably arose naturally as the result of a chance mutation. Breeders very likely seized the opportunity to preserve the mutants’ unique qualities and offer customers a new kind of sunflower. Apparently van Gogh was one such customer.

This article was published in print as "Beautiful Mutants."