Leaf Surfaces Are Hydrophobic

a green plant has a droplet of water on its surface surrounded by other leaves

Biological Strategy

Hairy lady's mantle

AskNature Team

Image: Krzysztof Belczyński / Flickr / CC BY SA - Creative Commons Attribution + ShareAlike

Protect From Excess Liquids

While water is essential to life, too much water or other liquids can overwhelm living systems. Excess liquids can, for example, decrease a living system’s access to oxygen, promote excessive bacterial or fungal growth, or strip away soil and nutrients. To prevent the accumulation of excess liquids, living systems must control the movement of liquids across their boundaries or surfaces. They do so using waterproofing materials or structures, slowing flow, and/or facilitating flow to move the liquid away. Plant leaves, for example, commonly have waxy surfaces comprised of water-repelling chemicals to keep water from engorging the leaves or facilitating bacterial and fungal growth.

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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 the Lady's mantle plant have a hydrophobic surface due to dense hairs.

“Ulrike Mock and others from the University of Freiburg report on efforts to mimic the wetting behaviour of surfaces or leaves of certain plants, especially the lady’s mantle (Alchemilla vulgaris L.) [Alchemilla monticola], which are rendered ultrahydrophobic through a dense layer of hairs grown on top of the leaf.” (Courtesy of the Biomimicry Guild)

“Recent studies showed that the most crucial criterion [for achieving the ‘Lotus Effect’] mainly relies on roughening the surface into multiple length scales of roughness so that liquid droplets can be retained in the Cassie-Baxter state, where air pockets are trapped underneath the liquid, reducing the solid-liquid interface. These hierarchically structured surfaces have been fabricated through various routes and demonstrated to have superhydrophobic properties as well. This amazing water-repellent property is also found in other biological systems comprising a plurality of flexible hairs, and some of them have been recognized for over 100 years. Fuzzy leaves, such as the Lady’s Mantle, cause water droplets to form perfect spheres and allow them to roll off easily as a result of being lifted and suspended by coming into contact with the hairs. In the animal kingdom, this piliferous exterior plays a more crucial role for numerous living creatures not only to effectively protect their bodies from getting wet but also to provide various functions for their living activity. These hairs protrude several micrometers from their cuticles, typically inclined at certain angles, with diameters in the micrometer to submicrometer range. These structures can resist the impact of raindrops, allow locomotion on the surface of water, or even trap a layer of air for respiration when submerged. Some arthropods have been shown to have contact angles above 150^o, which allows them to walk on water.” (Hsu and Sigmund 2010:1504)