Sunflower head. Close-up of the flower head of a sunflower (Helianthus annuus). The flower head of this plant, which can reach 35 centimetres in diameter, is a composite of many smaller true flowers (yellow/brown). Each flower develops into a seed after fertilisation. The sunflower is grown in warm climates as an ornamental. It is also cultivated for its seeds, from which sunflower oil is obtained.