The term "sunflower"
is also used to refer to all plants of the genus Helianthus, many
of which are perennial plants. What is called the flower is actually
a head (formerly composite flower) of numerous flowers crowded
together. The outer flowers are the ray florets and can be yellow,
maroon, orange, or other colors. These flowers are sterile. The
flowers that fill the circular head inside the ray flowers are
called disc florets. The arrangement of florets within this cluster
is typically such that each is separated from the next by approximately
the golden angle, producing a pattern of spirals where the number
of left spirals and the number of right spirals are successive
Fibonacci numbers. The disc florets mature into "seeds".
However, what we commonly call the seeds are actually the fruit
(an achene) of the plant, with the true seeds encased in an inedible
husk. Sunflower "whole seeds" (fruit) are sold as snacks,
especially in the United States and Europe, and as food for birds.