Why Do Floating Plants Have A Waxy Coating?


Water Lilies

Lately, I have been very interested in learning more about water plants, such as the lotus and water lettuce. Something that made me curious about these plants is the way they seem to absorb water without getting wet, and I found out it is because they have a waxy coating on their leaves. So I decided to study a bit more about it.

So why do floating plants have a waxy coating? Floating plants have short stems, and if not for the weight of the waxy texture on their leaves, these plants would get completely wet and sink underwater. The waxy coating locks in moisture and protects the plant from external threats.

Nature has provided all plants with some or the other form of protection against elements and external sources of danger. Floating plants are somewhere between completely submerged aquatic plants and terrestrial plants. They have as much interaction with the water ecosystem as with air. Due to this dual ecosystem, the waxy coating on floating plants is highly helpful to their survival. The waxy coating has more than one purpose for the benefit of floating plants. This type of coating not only prevents the plants from getting wet and submerged, but it also helps in keeping the plants hydrated and locking the moisture in.

Why Floating Plants have a Waxy Coating and how it helps them

To understand the many purposes of waxy coating on aquatic floating plants, it is also important to explore the constitution of this waxy coating- what it is made of. The waxy coating is a kind of cuticle, made of a substance known as cutin, which is a form of fatty acid that is waxy in texture. What the cutin does is equivalent to creating a thick film- a hydrophobic layer, insoluble in water and protective against water sources. This cutin is present in stems and other parts of desert plants as well as aquatic plants.

In desert plants, the waxy coating on fleshy stems preserves water and forms a screen that prevents loss of moisture. In aquatic and floating plants, often the purpose is to keep out excess water in such a hydrated environment and retain only as much water as required. As the cuticle is waxy, water from external sources cannot stick on the surface of the leaves, and internal water quantity is preserved for the use of the plant. The following are the prime reasons why floating plants have this waxy coating, and how it helps them survive-

  • A salient feature of floating plants is that they do not have a lot of structural material, that is, strong stems to support growth and build height. Technically, because these plants lack such structural support, they should be under threat of being submerged or getting swept away by the wind. But the waxy coating on the leaves of these plants holds them up and does not let them sink into the water.
  • Just because floating plants are aquatic, it does not entail that they are capable of thriving in excess water. Absorption of excess water in the plant cells would dilute and sweep away necessary nutrients, and would also bog the plant leaves down with water weight. But the presence of a waxy coating on the leaves keeps this water out.
  • The waxy coating on floating plants also provides protection against elements such as bad weather, high-speed winds, and heavy rain. Other than in cases of flooding, the waxy coating on leaves gives an added layer of security to the plants and makes the stem and leaves more resistant. Floating plants don’t have very strong stems, and thus the waxy coating solidifies them and helps them stay in their positions.
  • The presence of sap is important for every plant. Phloem sap flows through the entire plant, from root to stem and carries out important life-giving and sustaining processes every day. The waxy coating on the leaves of the floating plants protects them against depletion of sap due to natural processes such as osmosis. Thus, the waxy coating takes care of the balance of sap in the plant, and continually keeps the flow of sap maintained in the plants.
  • Since these are floating plants and not fully submerged, the leaves of the plants are exposed to the outside environment- air, sun rays, etc. Thus, the leaves are at a risk of losing moisture from within, which would then hamper all the processes in the plant and make it difficult to survive. Here again, the waxy coating on the plants prevents the issue by forming a barrier between the moisture withdrawing elements and the leaves. The coating ensures that the requisite amount of water is retained in the plant cells, and the outside environment cannot absorb this water from the plant.
  • The need for carbon dioxide in aquatic and floating plants is substantial, but floating plants don’t have as much difficulty in obtaining the same, as completely submerged plants do. However, too much of anything is not a good thing for any organism, even if they are nutrients. Too much intake of carbon dioxide, water and sunlight can be detrimental for such a plant. So the waxy coating on floating plants also acts as a medium between the carbon dioxide in the air and the plant, filtering in only as much of it as needed by the plant. The waxy coating similarly filters the level of sunlight as well, ensuring that the plant receives enough nutrition.
  • Apart from inclement weather conditions and natural elements, a threat to the health and well-being of floating plants is also disease by infection from certain organisms present in the air and/or water. If such organisms manage to penetrate the insides of the plants and stem/ leaves, the entire plant will decay soon and certainly show signs of weakness. However, that is what the waxy coating on floating plants is meant to prevent. The waxy coating on the leaves of these plants helps prevent such disease and disallows the infection from entering the plant.
  • Since floating plants are in and around water all their life spans, to ensure that there is no rotting of leaves or the stem due to so much water, the waxy coating on the leaves proves useful. In essence, the waxy coating is a thick protective layer that comes between the plant and all that is outside it. The waxy coating prevents dirt and other damaged or rotting plants from causing similar damage to the floating plants and its leaves and stem in particular.
  • In natural habitats, plants are susceptible to damage by insect bites and attacks. Insects can bite through the leaves and stem and cause damage, preventing the flow of nutrients and may also cause rotting. Aquatic plants and floating plants are prone to such dangers too, floating plants in particular at risk to both airborne insects and water insects. The waxy coating on floating plants also deters insects by denying them a surface to bite through, and protects the plants from such damage.
  • The waxy coating on floating plants is protective of leaves and the stomata therein as well. As photosynthesis is the life-sustaining process of any plant, the presence of this waxy coating protects leaves and helps in protecting the mesophyll layer, the same layer that comprises of photosynthetic cells. Moreover, the waxy layer is most often transparent, so sun rays are not prevented from reaching the leaves, and the photosynthetic cells can receive ample sunlight.

Thus, the presence of such waxy coating on floating plants not only aid and enhance their survival, but also increase their general life span by providing protection from various threats to their health. In some cases, the waxy coating can take on a bluish tinge which changes the color of the plant as well, but that does not hamper its productivity and role in helping the plant.

It has also been observed in some floating plants that this waxy coating is too thick, which can create an obstruction in the flow of nutrients. But in such cases, the plants have adapted accordingly, such as taking on underwater form like tape grass, or stronger root networks. The presence of this waxy coating in floating plants also enables the plants themselves to fulfill their own tasks of importance, such as keeping the water clean and purifying the water as well as air in many cases, maintaining a balanced ecosystem for the aquatic habitat.

Related Questions

What are some floating plants suitable for home ponds?

Floating plants can make a lovely aesthetic addition to the backyard and indoor ponds. Water lilies, hyacinth, duckweed, watercress (also edible!), hornwort, and parrot feather are some pleasing and easy to maintain floating plants which also purify the pond and clear it.

What adaptations do submerged plants have in order to survive?

Submerged plants are completely underwater and hence they have several features that help them survive- long, thin leaves with smooth surfaces and minimal cuticles to allow easy flow of carbon dioxide and nutrients, roots that act as mere anchors, and light structural composition with low plant height.

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