Ice in Rosette Protects Bud From Frost

close up photograph of leafy green plant

Biological Strategy

Lobelia

AskNature Team

Image: Forest Starr & Kim Starr / Flickr / Some rights reserved

Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Plants

Phylum Plantae (“plants”): Angiosperms, gymnosperms, green algae, and more

Plants have evolved by using special structures within their cells to harness energy directly from sunlight. There are currently over 350,000 known species of plants which include angiosperms (flowering trees and plants), gymnosperms (conifers, Gingkos, and others), ferns, hornworts, liverworts, mosses, and green algae. While most get energy through the process of photosynthesis, some are partially carnivores, feeding on the bodies of insects, and others are plant parasites, feeding entirely off of other plants. Plants reproduce through fruits, seeds, spores, and even asexually. They evolved around 500 million years ago and can now be found on every continent worldwide.

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A liquid held in the rosette of a lobelia protects the plant's terminal bud from frost by forming a shield of ice over the submerged bud on cold nights.

“There are also two species of lobelia on the upper slopes of the mountain [Mount Kenya]. Both form giant rosettes of leaves on the ground. They are in just as much danger of having their terminal buds frost-bitten as the cabbage groundsel and one of them takes the same preventative measures, folding its leaves over the terminal buds each night. The other surprisingly does not do this. Instead it remains widespread throughout the night. But it has a most ingenious defence…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.” (Attenborough 1995:261-263)