Thermogenic plants have the ability to raise their temperature above that of the surrounding air. Heat is generated in the mitochondria, as a secondary process of cellular respiration called thermogenesis. Alternative oxidase and uncoupling proteins similar to those found in mammals enable the process, which is still poorly understood.
The role of thermogenesis
Most scientists are not completely sure why thermogenic plants generate large amounts of excess heat, but most will agree that it has something to do with increasing pollination rates. The most accepted theory, states that the produced heat helps in spreading chemicals that attract pollinators to the plant. For example, the Voodoo lily uses heat to help spread its smell of rotting meat. This smell draws in flies which begin to search for the source of the smell. As they search the entire plant for the dead carcass, they unknowingly pollinate the plant. In this particular case, heat helped spread a scent, which in turn helped pollinate the plant.
Other theories state that the heat may provide a heat reward for the pollinator. By giving off heat, pollinators will be drawn to the flower to warm up. While the insect is getting heat, it will also be pollinating the plant by spreading pollen that is stuck to its body. This theory is less supported, because most thermogenic plants are found in tropical climates.
Yet another theory states that the heat helps protect against frost damage. This would allow the plant to germinate and sprout earlier than normal plants. For example, the skunk cabbage generates heat, which allows it to melt its way through a layer of snow in early spring. The heat, however, is mostly used to help spread its pungent odor and attract pollinators.
Characteristics of thermogenic plants
Most thermogenic plants tend to be rather large. This is because the smaller plants do not have enough space to create a considerable amount of heat. Large plants, on the other hand, have a lot of mass to create and retain heat.
Thermogenic plants are also protogynous. This means that the female part of the plant matures before the male part of the same plant. This reduces inbreeding considerably. The only way the plant could get fertilized is from receiving pollen from different plants. This is why thermogenic plants release pungent odors to attract flies.
Examples of thermogenic plants
Thermogenic plants are found in a variety of families, but Araceae in particular contains many such species. Examples from this family include the eastern skunk cabbage, the dead-horse arum, the elephant yam and Philodendron selloum, also known as elephant ear. Contrary to popular belief, the western skunk cabbage, a close relative from the Araceae family is not thermogenic. The carrion flower (Amorphophallus titanum) also uses thermogenically created water vapor to disperse its scent - that of rotting meat - above the cold air that settles over it at night in its natural habitat.
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