Water Off a Duck’s Back, Botanically Speaking

Bleeding Heart, Spicebush, Jewel Weed: Unwettable Leaves. Why?

In the slanting afternoon sun after a passing shower and early in the mornings when the sun is low, we are dazzled by the shining beads of rain on the spicebush along the creek and the jewel weed growing thick in the wet bottom of the branch beside the house. Yesterday, this leaf-surface property of unwettability was apparent on the leaves of the Bleeding Heart beside the rock steps outside the back door.

I’ve often observed it, but never really thought much about it. What are the properties of the leaf surface that make them un-wettable and is this a random feature or does it have survival or other functional value, I finally wondered as I set about getting this image ready to post this morning.

I’m gathering resources to understand both nature’s means of beading water as well as the human-engineered nano-materials attempts to mimic nature. In addition, there is the opposite property of hyper-wettability also being exploited by industry. The end result of both properties (hydrophobic and hydrophilic) can be materials (like clothing and paints) that do not hold water, which has all kinds of microbiologic and cleanliness, odor-reduction and appearance advantages.

Off on another interesting rabbit trail–where I seem to spend so much of my time anymore, and have given up the notion that anyone else is dying to know what I found out.

Even so, it goes in my “commonplace book.” Do you know about commonplace books? No? Well, let me tell you….NAH.

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Fred First holds masters degrees in Vertebrate Zoology and physical therapy, and has been a biology teacher and physical therapist by profession. He moved to southwest Virginia in 1975 and to Floyd County in 1997. He maintains a daily photo-blog, broadcasts essays on the Roanoke NPR station, and contributes regular columns for the Floyd Press and Roanoke's Star Sentinel. His two non-fiction books, Slow Road Home and his recent What We Hold in Our Hands, celebrate the riches that we possess in our families and communities, our natural bounty, social capital and Appalachian cultures old and new. He has served on the Jacksonville Center Board of Directors and is newly active in the Sustain Floyd organization. He lives in northeastern Floyd County on the headwaters of the Roanoke River.

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  1. Well, I wrote a comment to this piece but somehow posted it on yesterday’s entry. Might explain alot about my problems with journaling as well as my need for a commonplace book (or maybe a map)!

  2. I’ve been interested in water beading on plants for years. I’m sure you know this but leaves that have waxy surfaces help a cohesive force to take place. Cohesion in water is where a water molecule is surrounded by other water molecules creating a sphere. Gravity flattens the dome of the sphere creating more of an ovoid shape.

    Adhesion of water creates sheet flow. There is no cohesive force to keep the water molecules together. Think of water flowing over a smooth surface.

    This is all from memory. That means it might be inaccurate. My memory is often inaccurate and getting increasingly more so in my advancing years!

    Now if I just knew what a commonplace book was.



  3. Please, please explain what a “commonplace book” is. I absolutely love reading your facts/ponderings, etc.

  4. The water repellent property of the leaves of plants such as Alchemilla (ladies mantle) is due to a covering of very fine hairs. And it’s very pretty.