Deniz Armani/Caltech, (INSET) Tobias Kippenberg/Caltech

Nature's oven.
Skunk cabbage uses a simple mathematical formula to keep itself warm.

The Zen of Skunk Cabbage

Skunk cabbage shares more than a healthy stink with its warm-blooded namesake: like skunks, people, and other animals, the plant produces body heat. Now, a clever mathematical analysis has shown that this rancid relative of the lily may have a beautifully simple thermostat.

Skunk cabbage (Symplocarpus foetidus) is widespread in the woods of northeastern North America and Asia. In the United States and Canada, it's derided as a smelly swamp dweller, but in Japan the cabbage is thought to resemble a monk in meditation and is called 'Zazensou', or 'Zen plant'. Researchers realized in the 1970s that skunk cabbage maintained a constant body temperature even in sub-zero weather (the only other plant known to do this is the Asian sacred lotus), and it was obvious that skunk cabbage's furnace was its spadix, or central stalk. But tracking the plant's temperature over time gave wobbly, chaotic data that looked too complicated to analyze. No one could figure out how it knew when to crank up the heat.

In the November issue of Physical Review E, Takanori Ito and Kikukatsu Ito, both of Iwate University in Morioka, Japan, show a way to simplify the problem. They borrowed a technique other researchers had developed to tease out the important variables in complex phenomena such as ecosystems or weather patterns. First, they tracked the spadix temperatures of two wild populations of skunk cabbage over time and compared them to the air temperature. After making sure the fluctuations were not just random noise, the team determined that the plant used only two or three pieces of information, or variables, to regulate its internal temperature. That meant the plant's thermostat had to follow a fairly simple rule, perhaps like the oven in your kitchen. If a high-end oven gets too hot, it turns itself off; it may also track how fast its temperature is rising or falling and the temperature of the kitchen outside, making adjustments accordingly.

"I think this is a neat little paper," says James Elsner, a meteorologist at Florida State University who specializes in chaotic systems analysis. "The way they've done it, they've been careful, and they've used the right tools." Ito and Ito are pleased with their results, but they're hot to trot with the bigger question: figuring out, on the molecular level, what the two variables used by skunk cabbage really are.

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