Sunflowers (Helianthus annuus) are annual plants native to the Americas, that possess a large inflorescence (flowering head). Sunflower stems can grow as high as 3m (10 ft), and the flower head can reach 30 cm (11.8 in) in diameter with large edible seeds. The term "sunflower" is also used to refer to all plants of the genus Helianthus, many of which are perennial plants.
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 what are traditionally called "sunflower seeds," but are actually the fruit (an achene) of the plant. The inedible husk is the wall of the fruit and the true seed lies within the kernel.
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.[1][2][3] This pattern produces the most efficient packing of seeds within the flower head.[4][5][6]