Flexibility Allows Twisting, Not Bending, in Wind

detail of a sedge grass against a blurry background

Biological Strategy

AskNature Team

Image: Lazaregagnidze / Wikimedia Commons / CC BY - Creative Commons Attribution alone

Protect From Wind

Wind subjects living systems to various forces, such as compression, twisting, turbulence, and tension. These forces put living systems at risk of losing the ability to perform life-essential functions, such as when a plant becomes uprooted. Wind can result from weather phenomena or rapid movement through the air, as when flying. Wind is typically not a constant or predictable force, so living systems must be able to function both with and without its presence by adjusting to its direction and speed. A good example is how plants’ leaves and stems are flexible so that they can align with the wind, rather than being battered by it.

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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 stems of sedges twist rather than bend in the wind due to their torsional flexibility.

“On a smaller scale, Ennos (1993a) found that sedges swing around in a wind rather than bending over, doing so with stems of remarkably low torsional stiffness.” (Vogel 2003:382)

“The mechanics of the triangular stems of Carex acutiformis was investigated by subjecting sections to bending and torsional tests. The stem was rigid in bending, being stiffened peripherally by lignified material around the vascular bundles, but because of its triangular shape it was vulnerable to local buckling. Despite being [sic] and narrow the stem was able to support the seed head, though it sagged appreciably towards the tip. In contrast the stem had very low torsional rigidity, both because of its triangular shape because the strands of lignified material were isolated from each other. In its lowland habitat this allows the drooping stem to twist away from the light winds, so reducing drag and the chances of self-fertilization. This method of reconfiguring is not possible in the shorter, stiffer mountain sedges which must withstand higher winds; many therefore have more circular stems which will be more efficient at resisting bending.” (Ennos 1993:123)