Certain tree seeds are known for their distinctive spinning descent, mimicking a helicopter’s flight as they twirl gracefully from their parent trees. This unique method of dispersal allows them to travel farther from the originating plant.
The Names for Helicopter Seeds
The common term “helicopter seed” describes the spinning motion of these seeds as they fall. Other informal names, such as “whirlybird,” “whirligig,” “spinner,” or “maple key,” are also frequently used. Botanically, these winged fruits are known as samaras. A samara is a type of dry fruit where a flattened, papery wing develops from the ovary wall, typically containing a single seed. This wing enables the seed to be carried by the wind.
Samaras are indehiscent, meaning they do not open along a seam to release their seed. The seed is either located at the center of the wing, as seen in elm trees, or positioned to one side, with the wing extending from it, as is characteristic of maple and ash trees.
How Helicopter Seeds Fly
The distinctive spinning flight of helicopter seeds, particularly those from maple trees, is due to a phenomenon called autorotation. As the winged seed falls, its asymmetrical shape and the placement of its mass cause it to spin around its center, much like a helicopter rotor. This rotation generates lift, significantly slowing the seed’s descent. This mechanism allows the seed to remain airborne for a longer duration, increasing its chances of being carried by wind currents.
Research has shown that maple seeds create a tornado-like vortex, known as a leading-edge vortex (LEV), at the front edge of their spinning wing. This LEV reduces air pressure above the wing, effectively pulling the seed upward and doubling the lift generated compared to non-spinning seeds. The slow, controlled descent provided by autorotation allows seeds to travel considerable distances from the parent tree, sometimes several meters to kilometers.
Trees That Produce Helicopter Seeds
Many common trees produce samaras, or “helicopter seeds.” Maple trees (Acer spp.) are widely recognized for their distinct double-winged samaras, often V-shaped or U-shaped, which are a familiar sight in late spring and early summer. Red, silver, Norway, and Japanese maples are prolific producers of these seeds.
Ash trees (Fraxinus spp.) also produce samaras, though theirs typically feature a single, elongated wing. Elm trees (Ulmus spp.) disperse their seeds via samaras where the seed is centrally located within a papery, often circular, wing. Other trees, such as the common hoptree, sycamore, and certain birch species, also produce winged seeds that exhibit a similar spinning or fluttering motion, aiding in their wind dispersal. This dispersal method benefits the trees by allowing seeds to colonize new areas and reduces competition for resources near the parent plant.