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Why are double-flowered Asteraceae varieties valued by gardeners?
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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.
Double-flowered varieties of Asteraceae are highly valued by gardeners primarily because they produce showier flower heads.1
In nature, these forms occur when a mutation causes most or all of the central disk flowers to be transformed into ray flowers. While these double-flowered plants typically cannot survive the competition found in wild environments, they are intentionally perpetuated in horticulture for their aesthetic appeal. Common examples of plants frequently cultivated in these double-flowered forms include chrysanthemums, dahlias, China asters, marigolds, and zinnias.1