Seedpod Spirals to Stay Aloft

a green winged seed against a black background

Biological Strategy

Sycamore maple

Sam Stier & AskNature Team

Image: Hans Braxmeier / Pixabay / Public Domain - No restrictions

Move in/Through Gases

Living systems must move through gases (which are less dense than liquids and solids) such as those in the earth’s atmosphere. The greatest challenge of moving in gases is that because the living system is heavier than the gas, it must overcome the force of gravity. Moving efficiently in this light medium presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag and increase lift so that they can stay aloft and take advantage of variable currents. Additionally, they must overcome gravity when moving from a liquid or solid into the air. The fairyfly, the smallest known insect, is a tiny wasp that must move through the air. To the wasp, air feels like a heavy liquid and to move through it, it uses special feathery oars rather than wings.

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Disperse Seeds

Plants disperse their seeds using a variety of mechanisms, including wind, rain, and attachment to animals. Seed dispersal can be important if plants growing too close together will compete for resources, such as nutrients and sunlight. Since plants are literally rooted in place, seed dispersal is also an important mechanism for expanding their range or reaching new environments.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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Seed shape and distribution of mass ensure self-orientation and autorotation.

Introduction

The sycamore maple (Acer pseudoplatanus), a large, spreading broadleaf tree growing to 115 feet (35 meters), has a deep, branched root system that provides stability in high winds. But maple trees aren’t just good at resisting the wind, they’re also ingenious in how they use it.

The trees produce winged seeds which spin as they fall. These are sometimes known as helicopter seeds or samaras, and similarly-behaving seeds have evolved in other plant species many times. No matter the orientation of the seed as it detaches from the tree, it quickly self-orients and begins autorotating. This slows the seed’s descent to the ground, giving the seed more chance to be carried away by a passing breeze.

The Strategy

How do sycamore maple seeds orient themselves and start spinning? It’s a balancing act. The seedhead (or achene) is heavier than the seed’s wing, while the wing is much broader, catching more air as the seed falls. In physics terms, the center of mass is different from the center of pressure.

As the seedhead falls slightly in advance of the wing, and the broadest part of the wing slows due to air resistance, the wing is forced to tilt with respect to the ground. As air rushes upward and encounters the tilted wing, it deflects away from the seed at an angle, pushing the wing in the opposite direction.

The falling seedhead, meanwhile, encountering little air resistance over its compact body, descends straight downward, functioning like an axle around which the wing now begins spinning. Gravity provides a steady diet of air as the seed continues to fall, while the rotating wing, resisting a quick return to Earth, keeps the opportunity alive for a passing breeze to shove the seed on a lateral journey, farther away from the mother tree.

The Potential

Samaras have already inspired new designs of drones and ceiling fans. Designs which self-orient and autorotate (in water as well as in air) are especially interesting for use in renewable energy technologies involving turbines.

Related Innovation

Innovation: Industry

Aerodynamic Ceiling Fan Inspired by Sycamore Seedpods

Sycamore Technology

The Sycamore Ceiling Fan from Sycamore Technologies has a single blade that provides high air flow and creates minimal noise.

Last Updated October 7, 2016

References

“Winged seeds or fruits…can be placed into one of two categories—plane-winged, in which the seed coat or fruit wall grows more or less symmetrically with respect to its longitudinal axis and generates a linear gliding flight, and autogyroscopically winged, in which lift is created by wings on the propagule that permit autorotation during free-fall…The behavior of autogyroscopic seeds and fruits is remarkably similar to that of a helicopter and results from the combination of angle of attack and sideslip generated by the slightly curved blade of fruit wing or seed wing. The local speeds developed at the tip of the wing are relatively high and, together with the corresponding moments, produce great dynamic stability. When viewed from above and below, the rotating wing sweeps out a shallow conical section with an area Ap (Figure 9.10). The angle subtending the longitudinal axis of the fruit or seed and the horizontal plane is the coning angle ß, the equilibrium condition between the centrifugal forces acting on the rotating wing (which produce a turning moment tending to force the wing into a horizontal position) and aerodynamic forces (which tend to displace the wing into the vertical position). Thus the coning angle is the result of moments due to centrifugal and aerodynamic forces.” (Niklas 1992:461,463)

Book

Plant Biomechanics: An Engineering Approach to Plant Form and Function

01/08/1992 | Karl J. Niklas

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Reference

“European maples and sycamores have an even more economical design. They are equipped with only a single wing, sprouting from one side. The balance between the weight of the seed and the length of the wing is so accurately matched that these seeds also spin…Even in a light breeze their tiny spinning helicopters can travel for very long distances across the…countryside.” (Attenborough 1995:19)

Book

The Private Life of Plants

21/08/1995 | David Attenborough

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