Why Do Water Plants Have Stomata on Upper Part of Their Leaves?

Water lily
••• Image by Flickr.com, courtesy of David Blaikie

In plant biology, stomata are small pore-like openings on the surface of leaves. These pores open and close when triggered by specialized hormones in order to facilitate the exchange of gasses or to limit the evaporation of water.

Water Lilies

Water lilies grow in ponds where their leaves generally float directly on the surface of the water or slightly above it. To thrive in this environment, like all plants, they have developed specialized features.

Stomata

All plant leaves need to breathe. The exchange of atmospheric gases is essential to photosynthesis, the process by which plants use sunlight to convert carbon dioxide and water into oxygen and fuel. Openings called stomata make this possible.

Where to Find Stomata

In most green plants, the stomata are located on the lower side of the leaves. According to biologists at Colby College the leaf of the water lily has about 460 stomata per square millimeter on the upper surface of their leaves while many other plants, like the garden lily, have none at all.

Hydration

Stomata are useful to drought-threatened plants because they can close to prevent dehydration. This is not an issue for plants growing in water. Instead, when it rains, some stomata are available for gas exchange on the water lily's large leaf surface.

Other Adaptations

In order to keep leaves above the water where stomata can function, the leaves of the water lily have a large number of spongy internal cells to promote flotation.

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