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Why do ants carry the achenes of some Centaurea species?
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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.
Ants are attracted to the achenes of certain Centaurea species because they feed on special parts of the achene wall.1
In the context of plant-ant interactions, this behavior is a form of myrmecochory (seed dispersal by ants). While some harvester ants are destructive and consume seeds entirely, other species of ants are drawn to specific, nutrient-rich appendages on seeds or fruits, such as the fleshy elaiosome (fat body), which they consume while dispersing the seeds. In the case of Centaurea species found in arid Mediterranean regions, the ants carry the achenes about to access these edible portions of the fruit wall.231