How does plunger pollination work in Asterales plants?

In the order Asterales, plants utilize a specialized mechanism known as plunger pollination, also referred to as secondary pollination. This process functions through the following steps:

• Pollen Collection: The stamens form a tube around the immature style, with their anthers facing inward. As the style elongates, it acts like a plunger, pushing the pollen out of the tube using specialized hairs located beneath the closed stigma.1
• Outcrossing: These hairs present the pollen to pollinators while the stigma remains unreceptive. This arrangement facilitates outcrossing by ensuring that pollen is moved between different individuals.1
• Self-Pollination: Once the stigma becomes receptive, it remains open to receive pollen from other plants for most of its receptive period. Toward the end of this cycle, if no outcrossing has occurred, the stigma curls downward to contact the pollen-covered hairs, enabling self-pollination to ensure seed production.1