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With Helianthus annuus, what is usually called the flower is actually a head (formally composite flower) of numerous florets (small flowers) crowded together. The outer florets are the sterile ray florets and can be yellow, maroon, orange, or other colors. The florets inside the circular head are called disc florets, which mature into seeds.

The florets within the sunflower's cluster are arranged in a spiral pattern. Typically each floret is oriented toward the next by approximately the golden angle, 137.5°, producing a pattern of interconnecting spirals where the number of left spirals and the number of right spirals are successive Fibonacci numbers. Typically, there are 34 spirals in one direction and 55 in the other; on a very large sunflower there could be 89 in one direction and 144 in the other. This pattern produces the most efficient packing of seeds within the flower head.

Sunflowers most commonly grow to heights between 1.5 and 3.5 m (5–12 ft). Scientific literature reports that a 12 m (40 ft), traditional, single-head, sunflower plant was grown in Padua in 1567. The same seed lot grew almost 8 m (26 ft) at other times and places, including Madrid. During the 20th century, heights of over 8 m have been achieved in both Netherlands and Ontario, Canada.

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review by . September 25, 2010
posted in Green Living
   Sunflowers seem, at first glance, to be the emblematic flower of summer. They stand tall, face the world, and reflect the sun which is the origin of life, in many respects. French artist Gustave Caillebotte's Sunflowers on the Banks of the Seine successfully conveys their energy on a midsummer mid-day.      But in Eastern Canada where I live, summer is brief, and the sunflower's time is limited. One of the loveliest and most haunting scenes of the end of …
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