Backyard Biology

Nature stories from my backyard and beyond

Nature Stories
skunk cabbage

Warm-Blooded Plant?

Friday, April 8, 2011

When I was young, I loved facts. Once you learned a fact, it was always there for you. It was like money in the bank, ready to be withdrawn and used whenever needed. You always knew it’s capabilities. A dollar was a dollar, no matter what you wanted to buy. You could always rely on it. Same with a fact. If you needed a bit of information, a fact was always there for you.

As I grew older, I learned about inflation. A dollar, while still useful for buying things, can’t always be relied on to purchase everything I thought it could. A dollar is not worth what it used to be. Same with facts. As I grow older, I find that my facts, while still useful in many instances, can also suffer from inflation. As my knowledge of the world grows I find that some facts just aren’t worth what they used to be.

One fact I learned at a young age was the difference between warm-blooded and cold-blooded creatures. According to one of my first biology textbooks, warm-blooded animals have a mechanism to keep their internal temperature warm and cold-blooded animals take on the temperature of their surroundings. Birds and mammals were warm-blooded while all other animals were cold-blooded. Here was a fact I could take to the bank and withdraw whenever I needed it. Until fact inflation set in!

The more I learned about the natural world, the more exceptions to this fact came my way. For instance, many insects such as bees and moths can -for a time - maintain a temperature quite a bit warmer than their surroundings, sort of like warm-blooded animals. Conversely, the temperature of some birds and mammals will drop when they are not active, sort of like cold-blooded animals. So much for my facts.

At least there is one fact I can rely on. Plants are cold-blooded. Who ever heard of a warm-blooded plant. Plants don’t even have blood.
Well, it turns out some plants can generate their own heat, just like warm-blooded animals. One of these plants lives right in my back yard. It is the Skunk Cabbage.

Skunk cabbage is most known for its smell. Break a leaf and it smells like a skunk - hence the name. It is the earliest plant to flower in the woods behind my house. I have even found it pushing up through the ice and snow as early as February. Although the flower - technically called a spadix with a surrounding leaf called a spathe - is not much to look at, it is still surprising to see it in bloom under these conditions. skunk cabbage flowerHow is it that the plant is able to do this? By looking at the plant, it is clear to see that the ice and snow have not been pushed aside by the growing plant, but melted around the plant as it grows. The plant must be warmer than its surroundings. It must be generating its own heat.

A flower, of course, is the plant’s reproductive organ. Its purpose is to produce seeds that will lead to the next generation of plants. And that is the purpose of the skunk cabbage spadix. When it first blooms, it is a female flower, producing a stigma containing the egg. When the stigma is done blooming, the plant now becomes a male flower, with the anthers producing and releasing pollen. Now the trick is to get the pollen from the anther of one flower to the stigma of another, later blooming flower. This is the job of early flying insects. A number of insects have been found inside the spathe of the skunk cabbage, including numerous types of flies.

When I think of insects being attracted to flowers, I think of the sweet-smelling nectar that plants use to lure in the insects. Obviously this is not the tactic used by the skunk cabbage. Its odor is more like a skunk, or even of rotting meat. For a plant that blooms so much earlier than any other flower, this seems to make sense to me. This early in the year, there are no sweet-smelling plants to attract insects. Insects that key into these sweet smells would find little to nothing to support them, so they would not be out this early. However, there may very well be some putrid smells available, as any animal that has died during the long cold winter may have started to rot as the days get warmer. It is likely, therefore, that early flying insects will be attracted to this odor - indicating a possible food source.

So the skunk cabbage produces its foul odor to attract pollinators. To be effective in luring in insects, it must get the word out. It must advertise. The shape of the spathe and the heat produced by the plant help accomplish this. As the air inside the spathe heats up, it rises and exits the top of the flower, drawing in cooler air at the bottom of the flower. This warm air exiting the plant carries the odor with it. With a number of plants in one area all releasing their odor, the area is soon permeated with a slightly skunky smell -- a sure lure to any fly looking for a meal.

By generating its own heat, the skunk cabbage is able to emerge while the ground is still frozen and to attract the early flying insects. Studies done by R.M. Knudson in the 1970’s shows that the skunk cabbage can raise its temperature an average of over 30 degrees above the surrounding air. My own experiments show a much more modest increase (see Nature Activities Skunk Cabbage Temperature). Whatever the temperature difference, it seems that the skunk cabbage is a warm-blooded plant. And that’s a fact you can take to the bank. For now.