Slime Inhibits Evaporation

close up of a bright green plant in the shape of spiked rosettes

Biological Strategy

Giant lobelia

AskNature Team

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Protect From Loss of Liquids

Water is essential to life. Liquids, mostly water, make up 70 to 90% of all living systems, and the loss of even a small percentage can mean the difference between life and death. Living systems must maintain a proper liquid balance, which is especially difficult in dry conditions. To do so, they must control the movement of liquids across their boundaries. Living systems do this using structures or waterproof materials to prevent or slow liquid movement. For example, when humans receive a cut, they must limit blood loss. Scattered throughout the bloodstream are lens-shaped structures that serve to plug the wound.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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The fluid secreted and held in the rosette of one lobelia plant avoids water loss via an evaporation-inhibiting slime component.

In one species of lobelia that grows on the upper slopes of Mount Kenya, “Its rosette forms a deep watertight cup that contains up to three quarters of a gallon of liquid. Each night, a plate of ice forms across the surface. This acts as a shield, preventing the frost from penetrating more deeply into the pond. The water beneath remains liquid and therefore above freezing point and the submerged bud survives undamaged. It is a minimal defence. Were the nights to last a few hours longer or the temperature to stay below zero during the day, then the contents of the ponds might freeze solid right to the bottom and the bud would be killed. As it is, however, the sun returns after a few hours and all is well…But now the lobelia faces a different hazard. If the sun shines so hotly during the day that the water in the pond evaporates, then the lobelia would be defenceless when night fell. However, this does not happen. The fluid in the pond is not rain water. Indeed it cannot be for very little rain falls on these slopes. The plant has secreted it from special glands and it contains a slime that inhibits evaporation. So even during the hottest afternoons, its defence does not vanish.” (Attenborough 1995:263)

Last Updated March 27, 2018

References

Book

The Private Life of Plants

BBC Books | 21/08/1995 | David Attenborough

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Reference

“Lobelia keniensis, a giant rosette plant endemic to the alpine zone of Mount Kenya, secretes a solution of water and a mucilaginous substance. This solution forms a reservoir of up to 3 liters between the closely appressed leaf bases of the rosette. Experiments reported here show that rosettes drained of this liquid experienced bud temperatures well below freezing, whereas control rosettes never experienced bud temperatures below freezing. The presence of the reservoir did not affect the rate of leaf warming in the morning. The mucilaginous substance was identified as a pectin, which probably reduces evaporation from the reservoir without lowering the freezing temperature of the water.” (Young and Van Orden Robe 1986:267)

Journal article