Lace up your boots and follow me on a nature hike through these low Berkshire mountains of Western New England in early March. The air is thick with sunlight, as the red oak trees and alders haven’t yet leafed out, and their branches are just the latticework of a window on the sky. The ground still has a cover of snow, but you can smell the melting water beneath it as last Autumn’s leaves exhale a musty yet bread-like scent. Except for a few cedars, nothing is green yet. Nothing, except for some ugly, purple-green spikes sticking out of the snow. Come to think of it, they’re not so much sticking out as they are simply uncovered, as if the snow was too repulsed to touch them. And come to think of it, it’s not just fresh snowmelt you’re smelling. The woods have taken on the distinctive smell of buttcheese. You approach the ugly, stinky butt flowers.
Now, stick your finger in it.
To your surprise, it’s warm. Heck, it’s hot. It’s so hot, in fact, that it’s melted the snow around it. It’s a skunk cabbage, and during these early months of Spring, it can produce enough heat to stay between 60 and 95 degrees F above the ambient temperature. In doing so, it metabolizes as much oxygen as an animal of its size, and produces more heat energy than a flying hummingbird. Many cold-blooded animals have the ability to generate heat, but there are only a few thermogenic plants in the world, including the skunk cabbage, the water lily, the titan arum, and a few others.
Why Symplocarpus foetidus produces heat has both obvious and complicated answers. You can plainly see the advantage to being able to melt snow if you’re a plant in a cold climate. But why rise so early in the season? What insect pollinators are there that are out in the snow? Quite a few, actually: cold-tolerant flies and bees that can warm themselves by shivering their own wings. To attract them, the skunk cabbage produces no elegant floral perfume; maybe you can catch more flies with honey than vinegar, but you can catch more flies with rotting meat than honey. So the skunk cabbage takes after its distant cousin, the titan arum or “corpse flower,” by producing a righteous stink that serves the dual purpose of attracting hungry flies and dissuading hungry deer. There is the other reason to produce heat: it coerces scent molecules to vaporize and spread the smell further. What’s more, the cold insects have a cozy little lodge where they can warm up, which is especially important because the male skunk cabbages flower a few days before the females, and so need to entice the flies to vacation there for the weekend. Come for the smell of rotting badger carcasses, the plant says, stay because it’s too cold outside to leave.
To ensure a pleasant stay for its carrion-hungry guests, the skunk cabbage not only generates heat, but regulates its heat, like an animal. It’s climate-controlled. The thick, spongy leaves of the spathe, that purplish spike that encloses the flower itself, makes great insulation. And because the hot air inside the spathe must escape, the plant has its own ventilation system, with warm, meat-scented air rising out of its “chimney,” and cool, fresh air entering through the sides. As for structural foundation, the skunk cabbage’s roots actually pull it deeper into the soil every year, burying the crown and making it seemingly impossible to dig up. In other words, the skunk cabbage grows downward, not upward. Truly, it is one of the most state-of-the-art insect hotels ever invented.
So, we know that the skunk cabbage produces heat to melt the snow, to advertise its scent, and to entice insect tourists to come in from the cold. The trickier question is how it does it. Plants don’t burn fat for fuel, and they don’t shiver. Usually, a plant — or a human, for that matter — burns sugars to create ATP, a chemical that is the basic currency of energy in the body. We are not powered by heat, but by ATP. But during the two weeks of a skunk cabbage’s thermogenesis, it produces an uncoupling protein in its mitochondria that divorces its electron transport pathways from the ATP cycle. As a result, its glucose is “wasted” as heat instead of transformed into usable ATP. If you have to heat your house in the winter, and think of ATP as money, and could have your heating bills taken directly out of your paycheck each week… you get the picture.
Normally, we spend ATP (chemical money) to generate heat by burning fat. But humans can pull off the same trick as skunk cabbages, generating heat instead of generating and then using ATP. And the answer, once again, is brown fat, the mitochondria-laden, energy-burning fat that keeps us warm as newborns. (Is there anything brown fat can’t do? I want to spread it on my toast!) And we do it once more, at the other side of our life, i.e. when we’re dead. Of course, this is accomplished not by electron pathways, but as a byproduct of decomposition by bacteria. The carbon in our bodies, when oxidizes by microbes, releases enough heat that a corpse left in the woods in a New England winter can actually melt the surrounding snow. (Don’t ask me how I know this.) So the skunk cabbage, though using a different system, is not just effecting the odor of death, it’s mimicking the heat generated by decay. For a stonefly, which must trust its sense of smell more than its eyesight, the deception is nearly complete. The skunk cabbage may be the first harbinger of Spring in these parts, but really, it’s the last vestige of the long season of death. A little bit of Halloween to welcome in the new year.