Between late February and May, in woodlands and wetlands throughout eastern Canada and the northeast United States, you’ll find a low growing, foul-smelling plant called skunk cabbage (Symplocarpus foetidus). The skunk cabbage is one of the first plants to emerge in the spring when the winter snow is yet to melt. As the plant pokes its head out of the snow and starts flowering, it forms a small pool of water around it, created by snow melt. The heat needed to melt the snow is derived not from the sun but generated by the plant itself. Skunk cabbage is one of the few species in the Plant Kingdom, belonging to ancient lineages of flowering plants, that has the rare ability to generate heat — a phenomenon known as thermogenesis.
The flower of a skunk cabbage melts snow around it by its heat. Photo credit
Thermogenic plants are found in a variety of families, but Araceae in particular contains many such species. Skunk cabbage, the dead-horse arum, the elephant yam and Philodendron selloum, are a few examples of thermogenic plants belonging to the Araceae family. These plants can generate significant amounts of heat that even mammals can’t, and their rate of heat production actually increases the colder the environment gets.
In an experiment, skunk cabbages were found to maintain flower temperature 9°C higher when the air temperature was at 15°C. When the air temperature was dropped to –15°C, the flower was still at 15°C, or 30° higher than the air temperature.
The Asian sacred lotus (Nelumbo nucifera) can also regulate its flower temperature. Measurements showed that flower temperatures stayed at a warm 30°C to 36°C even when environmental temperatures dropped as low as 10°C. Another species Philodendron selloum is even better at temperature regulation. In lab tests, the flowers managed to stay between 30°C and 36°C even when scientists chilled the air to 4°C.
The dead horse arum (Helicodiceros muscivorus), another obnoxious smelling plant, reportedly produces more heat than any other known plant or animal considered in its entirety.
Knowledge of heat generating plants date back more than 200 years but it’s only recently researchers have started to unravel the biochemistry behind it. It’s now know that the heat is generated in the mitochondria, as a secondary process of cellular respiration, although the actual process is still poorly understood.
Biologists believe thermogenic plants generate heat to assist in pollination. The heat renders the flower’s fragrance more volatile which helps the scent to spread more widely so that pollinating insects can find them from far away. The dead horse arum, which smells like rotten meat, uses heat not only to attract flies and beetles but also to convince them that it’s a dead carcass. The heat also makes the thermogenic plants attractive to insects seeking warmth and comfort.
But a flower that offers pollinators just a sip of nectar or a snack of pollen and then sends them on their way has a better chance of dispersing its pollens than a flower that traps insects for a whole night by its hospitality. This is why thermogenesis is not commonly seen among plants. During evolution these heat generating species died out and were replaced by plants having better pollination methods.
The dead-horse arum. This flower has the fragrance of a rotting carcass. Photo credit
Skunk cabbages blooming in the forest. Photo credit
Skunk cabbage breaking through the ice. Photo credit
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