Sunflowers, originally native to North America, are cultivated for the flower trade and for the production of oil. There are many varieties of sunflowers but only a handfull are available as a wholesale cut flower.
An interesting fact about sunflowers, is that the stems were used to fill life jackets because of their bouyant properties.
NB. The foliage on sunflowers is usually shabby because all the energy is focused on the flower - never use Flower Food on Sunflowers as it will kill them!