Weak Leaves Deal With Strong Winds

a red orange leaf curls on itself to protect against wind with a blurry green background

Biological Strategy

Tulip poplar

AskNature Team

Image: Jens Dahlin / Flickr / CC BY NC ND - Creative Commons Attribution + Noncommercial + NoDerivatives

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 leaves of trees deal with strong winds by adjusting their configurations in order to reduce exposure and limit flutter.

Image: H. Zell / Wikimedia commons /

Leaves of the tulip poplar (Liriodendron tulipifera)

“Leaves–trees, really–have a problem, the same one as our solar panels. Their function, trapping solar energy photosynthetically, demands exposure of lots of area skyward…[Nature] arranges leaves and their attachments so they adjust their configurations and thus reduce their exposure and flutter as the wind increases. Motive force presents no problem, even for these nonmuscular structures, because the wind itself provides more than enough. Photosynthesis? Intermittently strong winds come mostly with reduced sunlight, so temporary reduction in exposure to sky can’t entail a great long-term cost…Figure 1.5a shows what one kind of leaf, that of a tulip poplar, does at a series of increasing wind speeds. This curling into a tightening cone characterizes quite a few kinds of leaves–including maples, sweet gums, sycamores (plane trees), and redbuds…All are characterized by relatively long petioles (leaf stems) and lobes on their blades that protrude back toward their parent branches from the point of attachment of their petioles. What appears to happen (based on observation and crude models) is that the lobes, upwind because leaves always extend downwind like kites on strings, bend upward (abaxially, technically) and get the curling started…This curling into cones dramatically reduces drag–at least if we pick the right item for a comparative baseline…Another wind-dependent reconfiguration, one in which the leaflets of a pinnately compound leaf such as black walnut or black locust roll up around their axial rachis, does a bit better…The very stiff leaves on a branch of a holly (Ilex americana) swing inward toward the branch and lie, one against another, in a common sandwichlike pile. Pine needles cluster instead of being splayed outward…The solution…involves two aspects as common in nature’s technology as they are rare in our own. First, shape isn’t held constant, but rather shape and the forces of flow interact complexly, each dependent on the other. The local wind forces on a leaf depend (in part) on its shape; its shape, in turn, depends (in part) on the local wind forces. Second, variable circumstances are dealt with by altering functional priorities. Photosynthesis, overall, matters far more than drag minimization; in storms, though, such priorities must reverse.” (Vogel 2003: 8-10)