The superhydrophic surface of nasturtium leaves
Flowers & Herbs, Garden of Eatin'

The Superhydrophobic Surface of Nasturtium Leaves

Rain doesn’t happen too often in Southern California, but when it does, I always love the gleam it brings to the garden. And literally, too — the wide-spreading patches of volunteer nasturtium vines seem to sparkle with thousands of Swarovski crystals after a good storm.

Water droplets on nasturtium leaf

Nasturtium leaf showing the lotus effect

Sometimes the raindrops roll off the leaves, or bounce as soon as they land, but many will pool on the lily pad-like surface and stand still until a breeze blows them away. They may even form patterns along the veins, as if Mother Earth just finished bedazzling her blanket of nasturtiums.

No matter how hard or how much it rains, they just don’t seem to get wet. Unlike most leaves in the plant world, water doesn’t spread and soak into a nasturtium leaf; when water hits the surface, the droplet bursts into many smaller droplets that bounce along until they finally settle or fall off. It’s an extraordinary adaptation that only a few plants exhibit, the most well-known being the lotus leaf, along with lady’s mantle, prickly pear, and certain cane species.

Beads of water on nasturtiums

The extreme water repellency of these plants (or superhydrophobicity, in scientific lingo) is the result of natural evolution to assure their survival. In the jungles and other wet environments where these plants thrive, sunlight is very limited. Frequent downpours wash dirt and dust onto the plants, leaving tiny particles that prevent light from penetrating the leaves. Since this can interfere with photosynthesis, nanostructures on the leaves inhibit water from absorbing. Instead, the droplets roll across the surface collecting dirt and other contaminants in their path, in effect cleaning the leaves — a phenomenon known as the lotus effect.

The lotus effect also protects plants from pathogens (like fungi or algae) that try to adhere to the leaves, and helps cleanse the bodies of insects like butterflies and dragonflies. Think of it as a biological housekeeping service!

Computer-generated detail of the lotus effect

Image by William Thielicke.

Though nasturtiums look and feel silky smooth, zoom in on a leaf and you’ll find a landscape of microscopic mountain-like structures. Each “mountain” is covered in waxy nanocrystals. The bumpy texture traps air between leaf and water, forcing the water to bead and perch on the peaks, rather than sit and spread in the valleys. With nothing to anchor them, the droplets roll around with little contact resistance until they fall off the edge of the leaves.

Superhydrophobicity of nasturtium leaf

Water droplets on water-repellent nasturtium leaf

Superhydrophobic surface of nasturtiums

As someone who’s outside a lot, using or wearing a variety of tents, sleeping bags, rain shells, and hiking shoes, water repellency is something I’m always seeking out in gear. And all of this made me wonder — why aren’t scientists creating the world’s most waterproof fabric from nasturtium leaves? Can they surpass the gold standard of Gore-Tex? (Which is essentially just Teflon-coated fabric.)

Turns out, they’re working on it. An engineering team from MIT has developed the “most waterproof material ever,” inspired by nasturtiums and butterfly wings! Looks like botanically-built adventurewear may be in my future.

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  • lookitskate

    This is really cool! I’m growing them for the first time this year (hoping they’ll take over and blanket a problem area on the side of my house) and I’ll be sure to take a peek at them after it rains 🙂

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