Sunflowers (Helianthus annuus L.) are large, erect blooms of the Asteraceae family. From dwarf varieties that reach about 4 feet in height to full-sized, towering cultivars that can grow 12 feet or taller, sunflowers enhance gardens and kitchens alike. Most of the 80 sunflower species are tolerant of temperatures ranging from 64 to 91 degrees F. Sunflower blooms and leaves follow the sun, no matter where they are planted, in a process known as heliotropism.
Sunflower seeds are actually individual one-seed fruits called "achenes," formed from the inferior ovaries of the disk florets. Used for oils, animal feed and food products, the sunflower seed is the final product of the sunflower's reproductive process.
The sunflower root structure is comprised of a taproot and a supporting group of lateral surface roots. The taproot is a solitary, prominent root that drives directly downward in search of moisture and nutrients. Lateral roots shoot out horizontally from the top of the taproot to provide support for the weight of the sunflower as it continues to grow.
The dicot stem structure of the sunflower is comprised of several layers of vessels that deliver moisture and nutrients to the plant through all phases of growth. The outer epidermis protects the intricate structure, beginning life in a round shape that becomes woody in nature as the plant ages. Sunflower stems grow without branching, and hold a single flower.
Sunflower leaves are bright green in color, heart-shaped and covered with finite hairs. When the sunflower reaches the bloom stage, the foliage and stems fade to a grayish-green shade.
The bloom of the sunflower is known as a composite flower, comprised of up to 2000 individual disk-and-ray flowers. Situated on a receptacle, each disk floret is a perfect flower, containing a stamen and pistil. The ray florets are sterile and do not produce seed. Pollination begins at the outer rim of the disk and moves toward the center. It takes 30 days after pollination is completed for the inflorescence to reach maturity.