The Backyard Naturalist – Hallowed Mysteries of the Skunk Cabbage
It’s not that there is no green to be had in late winter. The waxen gray-green of the pines, hemlocks and rhododendrons in their reliable military drab keep you from starving for color, but by late winter the eye craves brightness.
While there is still snow cover, before even the crocuses are up, you can find one of the very earliest flowers spearing up in swampy areas: the skunk cabbage, homeliest of names, humble in habitat, foul smelling. Before its leaves ever unfurl in a little snow cave of its own melting, the burgundy-sheathed flower generates heat, burning stored starch and running its cellular machinery as a furnace, sacrificing power for warmth, like we do when our muscles shiver rather than contract.
The flower’s anatomy is all named: the spathe, the spadix, and the words as I read them transport me in memory. At first I think it must be to the dissection lab in veterinary school, learning the words for every part of a dog, but the memory is more ancient than that still. It’s of serving at the altar as a child, learning the parts of the church, of the priest’s robes: the narthex, the nave, the alb and chasuble. An Asian relative of our skunk cabbage is known as zazensou, the Zen flower, for its resemblance to a monk (sou) with his cowled robe drawn up, meditating (zazen). The spadix, which is the knob-headed bundle of petalless flowers, is the part of the plant that emanates heat. This would seem a fine adaptation for a cold-climate plant, but in fact it’s a trick many members of the arum family know, and most of them live in the tropics.
The fever these plants run, therefore, didn’t evolve for melting snow, and many hypotheses have been put forward as to what advantage such a skill might confer. The flowers are pollinated by insects, and the heated spadix may better diffuse its carrion-scented perfumes on air warmed above the ambient temperature. Or maybe the heat merely encourages the insects to stay longer once they find the flower, invigorated by the warmth, crawling more enthusiastically over the stamens, picking up and depositing more pollen. Or maybe the pocket of warm air completes the illusion begun with the smell of decomposition by simulating the heat given off by a rotting animal body drawing flies.
There are plenty of examples in plants and animals of freeze tolerance or freeze avoidance — stored sugars, other molecules that keep ice from forming — but what skunk cabbage is doing is more complex. The flowers don’t generate heat at a constant rate, but in response to the air temperature around them. They modulate their metabolism to maintain a consistent body temperature, something like a mammal or a bird, using more oxygen and starch on colder days to strive for this set point. The temperature control is well coordinated through the two weeks or so that the female reproductive structures are developing. The male portions of the flower mature later, avoiding self-pollination, and at that point the thermostat breaks down and the flower’s temperature is no longer so tightly regulated.
What is it that requires such careful thermoregulation in the flower? Studies of insect visits to the plants show surprisingly few. Occasional bees, a fly here and there. In a late winter landscape where so little is flowering, we might expect the skunk cabbage to draw hordes of potential pollinators, but that does not seem to be what the heat production is about. Its adaptive function, if there is only one, is still unknown. In the late winter swamps, in the cupped hands of the spathe, the skunk cabbage holds its holy mysteries.