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How do plants float?

You can see many different aquatic plants in the Victoria house whose leaves and shoots float on the surface of the water. Air-filled tissues in various parts of the plant provide the buoyancy that allows them to float.

In the Ludwigia helmithorrhiza in front of you, parts of the root tissue are filled with air. You can see the thick, white roots, which look something like puffed rice.

Similar white coloring is visible on the shoots of Neptunia oleracea, a member of the mimosa family. Recognizable by its delicate yellow flower clusters, its long shoots rest elegantly on the surface of the water.

A similar but invisible air-filled tissue is found in the swollen leaf stalks of the water hyacinth, Eichhornia crassipes. It floats freely on the water and bears attractive clusters of blue-violet flowers. Though originally from South America, it was introduced into African lakes and reproduced so quickly that it is now an obstacle to navigation in some areas.

Another free-swimming aquatic plant, the water lettuce or Pistia stratiotes, is covered with fine water-repellant hairs that trap air. The leaves of the water lettuce are arranged in rosettes that do indeed make it look much like a small head of lettuce.

Leaves can also float by themselves. The many water lilies in this pond have air-filled leaf veins that let them rest on the surface of the water.

As you can see, aquatic plants are capable of many variations on a common theme, but they all use air to make themselves buoyant.



Audio file download
How do plants float? (MP3, 757 KB)

Audio production and copyright: Soundgarden Audioguidance GmbH
Text: Günter Gerlach, Botanischer Garten München-Nymphenburg