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What Makes Water Lilies Float?

Image by, courtesy of David Blaikie

Sometimes considered a pest if they overrun a pond, but most often the centerpiece of a water garden, water lilies have entranced garden enthusiasts through the ages. Floating serenely on a still pond, a blooming water lily has undoubtedly made more than one gardener wonder, “Just what keeps them afloat?”

Lilies Love the Water

Nymphaeaceae, or “water lilies,” a family of flowering aquatic plants, thrive in freshwater ponds and still bodies of water in temperate and tropical climates around the world. Although they may seem to be floating, water lily roots are actually firmly planted in the soil beneath the water.

Breaking the Surface

Water lilies sprout beneath pond waters from a network of tubers, or rhizomes. Slender stalks push up to the surface of the water, where leaves unfurl and buds will set and soon bloom. Tropical water lilies require warm temperatures to grow, usually above 70 degrees F, while hardy water lilies (most common in North American and other temperate climes) can grow in cooler waters. During winter, water lily tubers do not die off but lay dormant.

A Water Lily’s Floating Features

Water lilies are well equipped for life in the water, with a stem structure that contains a tough network of bundled hollow cells that hold air and help stems float. Once leaves unfurl, their large surface area offers the plant additional support by using water surface tension to keep the plant afloat.

Taking Advantage of Water Tension

Water molecules at the surface of a body of water have a stronger attraction to each other than the molecules beneath the surface, creating what is commonly called water surface tension. Similar to the method water insects use to skim across a pond’s surface, water lily leaves may have small hairs or other structures to take advantage of water tension. The still water of ponds and marshes ensures water lilies have plenty of water surface tension to help them float.

A Little Leaf Support

Water lily leaves are particularly adapted for water life, with the primary cells used for photosynthesis on the top surface of the leaf that faces the sun. A waxy layer, or cuticle, coats the top of the leaf, repelling water so that the plant can “breathe” and to drain off excess water and keep the leaves from sinking.

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