Iowa wildflower Wednesday: Celebrating skunk cabbage

Luther College Associate Professor Beth Lynch educates the Bleeding Heartland community about a rare early spring wildflower. For those who missed it, I highly recommend her post about witch hazel from last October. -promoted by desmoinesdem

One weekend in early April the tourists showed up in town. They were thicker than flies around here. I’ll admit that most of them were here for a new beer release at one of the local breweries, but I also spotted some wild plant tourists tromping around the woods in search of skunk cabbage.

Skunk cabbage is not the first plant to bloom each spring. That award almost always goes to the silver maple trees. And, it is certainly not as cute as the pussy willow buds. So, why are the tourists coming to see skunk cabbage in the mucky swamps around northeastern Iowa?

Skunk cabbage lives in cold, water-logged seepage wetlands, an unpleasant habitat on the damp chilly days of late-winter. These little wetlands occur where groundwater seeps out of hillsides, forming mucky areas that provide essential habitat for skunk cabbage, bright yellow marsh marigolds, and a diverse assemblage of less charismatic but intriguing native wetland species.

In March and April, the skunk cabbage plants are still mostly underground – a massive root firmly anchors the plants in the muck. Only the flowering structures are showing, and let me tell you that the flowers of the skunk cabbage are not classic beauties. Look down at your muddy feet, and all you will see is a mottled brownish cone poking through last year’s rotting leaves and the last of the winter snow.

Skunk cabbage is related to Jack-in-the-pulpit, a woodland wildflower common throughout Iowa. In both species, the flowers are very small and inconspicuous. They tightly cluster along a thick stalk (called the spadix) that is completely hidden underneath a hood (a modified leaf called a spathe).

The hooded flowers of skunk cabbage blend in with the surroundings at this time of year, so you have to look pretty hard to find them. Later in the spring, the huge, bright green, skunky-smelling leaves emerge from underground. As the leaves unfurl and form big floppy cabbages, the plants become much easier to see and, in my opinion, much more attractive than the early spring flowers.

So what, then, is the allure of the skunk cabbage, a plant with drab flowers and skunky leaves? If I were an insect, I might tell you that the reason I seek out skunk cabbage is for warmth. Skunk cabbage is one of a very small number of plant species that can generate its own body heat, a trick called thermogenesis. In fact, not only do the plants generate body heat by metabolizing carbohydrates stored in their massive roots, but they can regulate their temperature, generating more heat as the air temperature gets colder. Through February and March when outside temperatures can dip well below freezing, inside the spathe the plant keeps its flowers at a cozy room temperature (about 68° F).

While botanists have been able to describe how skunk cabbage regulates its body temperature, they still aren’t sure why the plants exhibit this unusual and metabolically expensive behavior. Possible explanations include protecting the flowers from frost damage or attracting pollinators to the flowers, either by enhancing their skunky odor or by providing a warm shelter. To this point, no one has put these ideas to a serious test, but there is very little evidence that potential pollinators visit plants during the period when pollination is required for their reproduction.

It might just be that cold late-winter temperatures inhibit another critical step in plant sex. When a flower is pollinated this means that pollen is transferred to the stigma of the plant. After pollination, the sperm cells still need to get from the pollen grain to the egg cell located deep within the tissue of a flower. This occurs through the growth of a pollen tube that delivers the sperm to the egg cells. Researchers studying an Asian sister species to our skunk cabbage found that when early spring temperatures are too cold, the pollen tube won’t grow. In this species, fertilization (transfer of the sperm to the egg), not pollination, is the critical step requiring the plant to generate heat when outdoor temperatures are too cold.

Why skunk cabbage flowers so early in the spring is a whole other question and no easier to answer. But, searching for these early spring wildflowers certainly provides a terrific excuse to get out in the woods, and I am happy to that skunk cabbage tourism is thriving in my neck of woods!

Reddish-brown flowering structure (spathe with spadix hidden inside) and young leaves emerging from a skunk cabbage plant in northeastern Iowa: