Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Skunk cabbage in snow © Gregory K. Scott

A biochemical reaction generates enough heat to melt surrounding snow, giving skunk cabbage a jump on the growing season.
© Gregory K. Scott

February 2010

Winter heat in the hood

Skunk cabbage gets growing right through the snow.

Anita Carpenter

Winter reluctantly releases its grip on Wisconsin's swampy, shaded wetlands. In early March, the rich earth, still snow-covered and frozen, is an inhospitable environment for any growing plant, let alone a flowering one. Yet one plant defies the season. The wine red flowers of skunk cabbage poke through several inches of snow and are thriving, blooming and attracting early flying insects.

You have to seek out skunk cabbage (Symplocarpus foetidus) for it is not a dramatic "here I am, look at me" kind of plant. Its large leaves that are so obvious in June have yet to unfurl and its uniquely shaped, earth-toned flowers hug the ground. Once you find them, they are unmistakable and worth a closer look.

Unlike typical flowers with colorful petals and sepals, skunk cabbage produces a spiral, sculpted hood called a spathe. This is really a single, highly modified leaf, which wraps around itself. Enclosed in the five inch hood and visible through its narrow side opening is a spherical, yellowish head of tightly packed individual flowers, called a spadix. The flowers have no petals but have four inconspicuous yellow sepals. When they bloom, the stamens grow up between and above the sepals to release pale yellow pollen. Then a female style grows out from the middle of each flower, ready to accept the pollen that is delivered by insects.

How can skunk cabbage grow in frozen soil and blossom in cold weather when others can't? It produces its own heat and creates a warm microhabitat where it can grow. When the springtime temperatures first start to rise above 32 degrees F, the spadix begins to oxidize starches that were stored all winter in the roots. A by-product of this biochemical reaction is heat; hot enough to thaw the immediate area surrounding the plant and encourage the hood to grow and open. The plant warms and retains heat in the space inside the hood that has a thick, spongy texture and acts as a good insulator.

Although the surrounding ambient air temperatures fluctuate, the spadix adjusts its respiration rate to maintain a fairly constant 70 degrees within the hood. For about two weeks, the internal toasty temperature keeps the spadix from freezing and enables the sensitive reproductive structures to develop and blossom. The heat also vaporizes foul-smelling substances that attract pollinators like flies, beetles and honey bees.

After pollination is complete, the hood slowly disintegrates. The spadix bends over and grows along the ground. By mid-June, the mature red fruiting heads, now two inches in diameter, contain round, berry-like fruits, each with a single half-inch diameter seed inside.

Observant flower watchers will notice a green, cigar-like leaf bud nestled next to the hood. In March, this bud bides its time waiting for warmer days. When the spadix tips over, the tightly rolled leaf bud starts to grow. From late April into May, bright green leaves unfurl and expand into large tobacco or rhubarb-sized leaves. Most people become aware of this plant when its leaves are large and showy in May. Crush a leaf and you'll appreciate how the plant earned its name.

By late June into July the watery leaves sort of dissolve and disappear. By August, the mature fruiting heads start to fall apart and the fruits on the ground are eaten, decompose or may germinate in the fall or spring. Skunk cabbage is a perennial, and individual plants may live a decade or more. Newly sprouted plants take at least seven years to produce their first flowers. In late autumn, you may see the next year's leaf buds and hoods already poking above ground but unopened. They will wait until late winter to make their own heat and reclaim the distinction as Wisconsin's earliest flowering native species.

Anita Carpenter gets an early start on her flower gazing every winter, her favorite season.