Skunk cabbage is coming in hot
I've given up on winter. It seems that nature around me has, too. This past rainy weekend, I ventured into a nearby marsh, wading through knee-high mud under cold, glowering skies that hinted of impending rain. Despite the cold, a few signs of new green life were emerging, plants that have been patiently awaiting the arrival of spring. Along the stream bank, mottled purple skunk cabbage (Symplocarpus foetidus) pierced through layers of wet, matted leaves and grasses.
If there had been snow on the ground, the skunk cabbage would have been poking up through that as well. Skunk cabbage, one of the first wildflowers to bloom in New England, uses its unique ability to generate heat to melt the frozen ground and snow (when present) above it, giving itself a jump on the season.
Skunk cabbages' heat is produced by its flower, a knob-like protuberance known as a spadix that emerges well before the large green leaves, protected by a modified hood-shaped, mottled purple leaf (the spathe). The space around the spadix can reach a whopping 70 degrees Fahrenheit! Enough heat to melt through snow as it flowers in early spring. While heat production (thermogenesis) in plants is uncommon, most of us have heard of plants that can generate heat due to the notorious corpse plant — a close cousin of skunk cabbage. Corpse plants live in the tropics so don't need to generate heat to melt through snow and ice, instead their heat is used to carry the delicious smell of rotting meat to wouldbe pollinating insects. As with the corpse plant, heat also helps the skunk cabbage attract early pollinators-most notably flies and carrion beetles-who enjoy a good meal next to the stove on a cold winters' day.
We don't often think of plants when we think of being warm-blooded or able to thermoregulate. So, how does skunk cabbage do it? We humans (and other warm-blooded animals) generate heat by burning sugars. Skunk cabbages do something similar. Like all plants, skunk cabbage needs to breathe. When it's time to start growing in early spring, hormonal changes trigger the mitochondria (the “powerhouse” of the cell) to start burning sugars that were stored in the underground stem, the rhizome. The skunk cabbage takes in oxygen (just like all plants), but when blooming, instead of using the oxygen to only burn sugars for cellular energy or work, there is a modified pathway that enables this chemical reaction (respiration) to release the energy stored in those sugars in the form of heat. The colder it is, the more oxygen the skunk cabbage takes in generating even more heat. According to the classic paper “Heat production and temperature regulation in eastern skunk cabbage” (R.M. Knutson, Science, 1974) skunk cabbage can maintain elevated respiratory rates for at least a couple weeks, while the flower is blooming, consuming oxygen at a rate comparable to that of warm-blooded animals of equivalent size.
Spring is just around the corner, which for me heralds one of my favorite late winter/early spring pastimeshunting for signs of spring. Invariably, thanks to thermogenesis, the blooms of local skunk cabbage are the first I discover.