How Are Sunflower Seeds Dispersed?
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Wind
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When most sunflowers "go to seed," they form structures that resemble tiny parachutes. The upper portion of the parachute, called the pappus, resembles hair and is extremely lightweight. A stem attaches to the pappus, and at the bottom of the stem is the seed or fruit of the sunflower. Wind catches the hairlike structures of the pappus and lifts the seed from the plant and into the air current. As long as the wind stays strong enough to hold the seed and pappus up, the entire structure stays airborne. It can be carried over many miles and every type of geographical structure, including mountains. When the wind dies down and can no longer support the seed and pappus, the seed and pappus come to rest in a new location. The new location can be drastically different in terms of soil content and structure and other foliage.
Animals, Birds and People
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Some types of sunflowers do not form pappus structures. These are transported most commonly by birds or animals who disrupt the seed from its position on the plant, intentionally or unintentionally. Large sunflower plants that produce the kinds of edible seeds found in grocery stores, for instance, are a favorite of birds, who land on the large flowers and peck away at the seeds and carry them away or cause them to fall on the ground. Other plants in the sunflower family, like the notorious cockelbur, have structures on the seed that get caught in the fur of animals or on clothing. The stuck burs eventually are worked loose and the seed is distributed in a new area. Additionally, any seed that falls on the ground can be kicked around by people and wildlife, or transferred when the dirt around the plant is transferred, such as during landscaping.
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Water
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Regardless of whether the seed forms a pappus, some sunflower seeds, either by wind or by the transport of animals, birds and people, get into bodies of water, such as rivers and streams. The current carries the seed downstream until it becomes lodged in the riverbed or bank, or until it is picked up again by another animal, bird or person. This tends to be less efficient than other forms of dispersion, because the seed can travel only in the path of the water, rather than across different geological structures as with wind or animal, bird or human dispersion. The seeds also sometimes rot due to the amount of water available prior to reaching a good place to germinate.
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