I was fascinated recently, while observing the water puddles on an agave leaf after a recent rain event this winter. These natural phenomenon are often missed as we hurry through life, or are even things we simply take for granted. In fact, each aspect of life is quite more complex than we realize.
The cause of the water puddle on the leaf is what’s known as epicuticular wax. This is the outermost leaf coating that acts as a final level of defense from the environment. The wax is actually a three dimensional set of tightly packed crystals, that work to reduce water loss, prevent water permeability, and provide resistance to insects and disease. This type of leaf wax is found in many plant groups including succulents, most grasses, water lilies/lotus, members of the Musaceae (bananas, cannas) family, Eucalyptus, Hosta, and members of the cabbage (Brassicaceae) family.
Many plants that have such epicuticular waxes are often difficult to treat with pesticides. In these cases, surfactants and sub-laminar penetrants must be added to the spray. As leaves with epicuticular waxes come in contact with the soils, microbial activity works to breakdown the wax, which is why you will often see damage to lower agave leaves which are in direct or splash contact with the soil.
Since these epicuticular waxes were first documented in 1871 (De Bary), they have been studied extensively, with advances coming in waves as our technology to study them continued to improve. Today, we know that epicuticular waxes are made of a combination of substances that include alkanes, aldehydes, primary and secondary alcohols, ketones, triterpenes, flavonoids, and fatty acids. The composition of the waxes are different from genera to genera, but also from species to species within the same genus. Some epicuticular waxes are very tolerant of high temperatures, while those on a hosta leaf will melt at temperatures around 90 degrees F. While some epicuticular wax can be removed manually, it will subsequently regrow as long as the foliage remains alive and actively growing. Research has shown that wax crystals can begin regrowth within a matter of minutes if the environmental conditions allow. Ain’t plants cool?
The beauty of science is that it is never static. Some people sadly believe that once you learn a scientific fact, it never changes. In reality, nothing is further from the truth. When you hear anyone purporting to be scientists, make a statement like, “You should believe x, because it is an established fact”, they have just let you know how arrogant and closed-minded they are. If we pay serious attention to people who utter statements like this, we’d still believe the Earth is flat. Remember that science is only the current consensus of opinion on a subject, that is subject to change when more data is received and analyzed.
Even the current consensus can be contentious, just look at nutrition or, apparently, botany.
In my opinion,
science is a process, not an institution.
Unfortunately, over the past decade science denialism and anti-science sentiments have been on the rise with many unintended detrimental affects. As demonstrated here can learn much from plants, both scientifically and culturally. That said this reminds me of the cautionary story about a blended family of tender but root hardy evergreen tropicals living in the temperate mid-Atlantic zone 7-8 region that took a hard pass on overwintering with their monocultural sub-tropical family in the deep south. The reasons being real and imagined ‘horticultural differences’. It seems this root-hardy, diverse, blended family would rather die to the ground and go dormant until spring than be exposed to such diametrically opposed and sometimes ‘thorny’ horticultural and agricultural practices. But after a few nights in the grip of a polar vortex that dropped temperatures into the teens, their foliage now toast, their metabolism slowed to a crawl; the family of now dormant tropicals made a joint decision that next year they would put aside their horticultural differences and overwinter with their relatives on the sunny southern beaches of zone 9-10 US. Because after-all, family comes first.