The sunflower blooms from July to October.
Immature plants whose flower bud has not yet been opened show heliotropism: during the day the flower bud turns with the sun on sunny days. At night, the flower bud returns to its eastern position. This daily movement is caused by uneven growth due to cell elongation of the flower stem. A sunflower has no pulvini (leaf cushions). By the time the inflorescence opens, the flower stem stiffens in its eastern position; heliotropism is then over. As a result, flowering sunflowers point east all day long.
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