The New World Flower That Follows the Light

The sunflower, Helianthus annuus, is native to the Americas and was domesticated in what is now the United States and Mexico for its edible seeds long before it reached Europe in the sixteenth century. Two natural facts drive its symbolism. The young flowering head is heliotropic, tracking the sun across the sky before settling to face east at maturity; and the seeds are packed in interlocking spirals whose counts fall on consecutive Fibonacci numbers, an arrangement that fills the head with near-perfect efficiency and has made the sunflower a standard example in the study of plant geometry.

Sunflowers have a genuine practical use in environmental cleanup: the plant is efficient at drawing radioactive caesium and strontium out of contaminated soil and water through its roots, a process called phytoremediation, and sunflowers were planted for exactly this purpose near the Chernobyl nuclear plant after the 1986 disaster and again near Fukushima Daiichi after 2011, a modern scientific use with no older correspondence tradition behind it at all. The heliotropism described above has a documented mechanism: a 2016 study by Stacey Harmer's group at the University of California, Davis, published in the journal Science, showed that young sunflowers track the sun by way of an internal circadian clock controlling which side of the stem elongates, and that the resulting eastward-facing habit warms the mature flower head enough to attract measurably more pollinators.