Tornado-like Spinning Increases Seed Dispersion

Biological Strategy

Japanese maple

AskNature Team

Image: Photo courtesy David Lentink / CC BY NC ND - Creative Commons Attribution + Noncommercial + NoDerivatives

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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Transform Mechanical Energy

Mechanical energy is made up of kinetic energy (the energy of an object in motion) and potential energy (stored energy). Organisms use mechanical energy in a variety of ways, including capturing prey, transporting seeds, and moving around.

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Distribute Solids

Solids include resources such as food, seeds, spores, and leaves, which living systems must sometimes move to accomplish various activities such as pollinating, feeding their young, or building shelters. To effectively distribute solids, living systems must use strategies appropriate to the sizes and types of solids and the media in which they exist (air, water, or another medium). This may entail strategies beyond simply holding and carrying solids. For example, some seeds are carried by the wind to new locations for germination. Others–like the burdock plant’s hooked seeds–cling to animal fur to be transported.

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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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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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The leading edge of the tornado-like spinning maple seed provides a constant lift force, allowing seeds to disperse over a greater area.

Introduction

Scattering seeds is a prominent mechanism in all plants, often assisted by birds and gusts of wind. When birds eat the seeds of trees, they transport and defecate them, creating a randomized scatter where new trees will grow. When caught in a gust of wind, seeds fall and end up growing in close vicinity to one another. To increase the reach of where their seeds are planted, maple tree seeds twirl in a tornado-like vortex, creating more lift than their non-twirling counterparts.

Image: Liz West / CC BY NC - Creative Commons Attribution + Noncommercial

These Japanese maple seeds are gearing up to twist to the ground using a sustained lift vortex to prolong their flight.

Image: Photo courtesy David Lentink / CC BY NC ND - Creative Commons Attribution + Noncommercial + NoDerivatives

This image shows the free-flight sequence of an auto-rotating seed as it falls to the ground. (Photo provided with permission from David Lentink and California Institute of Technology)

Image: Photo courtesy David Lentink / CC BY NC ND - Creative Commons Attribution + Noncommercial + NoDerivatives

A maple seed in a wind tunnel generates a prominent leading edge vortex near the base. (Photo provided with permission from David Lentink and California Institute of Technology)

The Strategy

The leading edge of the seed lowers the air pressure over the top of the seed, sucking the wind of the seed upwards, giving it extra lift, or extra travel time. This leads to a prolonged arrival at the ground, and more efficient dispersal.

The lift mechanism is similar to those of insects and hovering hummingbirds who use their wings to develop a continuous air vortex, sustaining their flight. The spinning motion created by the maple seed structure sustains a lift vortex which prolongs the flight. It’s also important to note that dead (brown-colored) seeds scatter further because they have an altered center of gravity from alive (green-colored) seeds. This is because the center of gravity in the seed is closer to the center of lift, similar to a paper airplane that is able to fly further than its opponents.

Falling Maple Seed: Watch a video of the tornado-like vortex of a free-flying maple seed (Movie courtesy of David Lentink):

The Potential

Through careful study of how a maple seed spirals through the air, scientists have designed the smallest known monocopter. Until the mechanics of falling seeds were better understood, monocopter flight was unstable. Investigating how maple seeds deal with turbulent air could also help develop more efficient wind turbines, increasing the amount of renewable energy that can be extracted from the breeze.

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Last Updated July 2, 2020

References

“Detailed performance studies revealed that autorotating seeds are able to generate unexpectedly high lift forces despite their small size and slow velocity. Like autorotating seeds, insect wings generate very high lift despite operating at angles of attack well above those that will stall conventional aircraft wings and helicopter blades” (Lentink et al., 2009:1440)

Journal article

Leading-Edge Vortices Elevate Lift of Autorotating Plant Seeds

Science, Vol. 324, Issue 5933, pp. 1438-1440 | 11/06/2009 | D. Lentink, W. B. Dickson, J. L. van Leeuwen, M. H. Dickinson

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Reference

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