The common sunflower (Helianthus annuus Linnaeus) is thought native to western North America; where and when first cultivated by native peoples is a source of conjecture. Natives in eastern North America, the southwestern desert, Mexico, and Peru were all growing the plant when Europeans arrived. The oldest sunflower seed, recovered from an archaeological dig in Tabasco, Mexico, has been dated to about 4130 before present. ("Discovery of Prehistoric Domesticated Sunflower Seeds Challenges Widely Accepted Theories...", NYBG, May 2001)
The sunflower is actually an inflorescence called a head or capitulum; the center is composed of disk flowers, the edge has ray flowers that appear as petals. Each disk flower produces a single fruit, an achene, containing a seed. The inflorescence matures from the edge toward the center--seeds are developing at the edge before the flowers in the center are even old enough to be pollinated. The size of the capitulum is not predetermined; it expands to accommodate additional developing flowers.
Sunflowers were taken back to Europe in the 1500s. John Gerard grew sunflowers in his garden in Holborn, London. In 1597 he wrote of the "golden floure of Peru...when the plant groweth to maturitie, the floures fal away, in place whereof appeareth the seed, blacke, and large...set as though a cunning workeman had of purpose placed them in very good order...." (The Herbal, 1633 edition)
Gerard's "very good order" is an interesting mathematical sequence. According to Przemyslaw Prusinkiewicz and Aristid Lindenmayer, the sunflower's "...most prominent feature is two sets of spirals or parastichies, one turning clockwise, the other counterclockwise, which are composed of nearest neighboring florets. The number of spirals in each set is always a member of the Fibonacci sequence; 21 and 34 for a small capitulum, up to 89 and 144 or even 144 and 233 for large ones." (The Algorithmic Beauty of Plants, 1990, Springer-Verlag)
The Department of Mathematics, Smith College has an excellent diagram and description of parastichies. To learn more, click on the link:
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