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How does flowering move from the outside to the centre of an Asteraceae flower head?
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Asteraceae
The flowering head of a sunflower (Helianthus annuus) is formed of yellow, petal-like ray flowers and a brown center of minute disk flowers.
In the Asteraceae family, the flowering sequence within an individual head is always centripetal, which is a characteristic of a racemose (indeterminate) inflorescence.1
This means that the flowers located in the outermost row or rows of the head bloom first. Following this, there is a progressive spiral of flowering that moves toward the centre of the head. As the older flowers mature and set fruit near the outer edge, younger buds continue to develop and expand into flowers as the process moves inward.12