I am most interested in plants which play a role in the life cycle of butterflies, either as larval hosts or nectar sources, but there are some plants which fascinate me in their own right. Skunk Cabbage is one of those plants. I enjoy seeking it out because it is one of the first, if not the first, of our native plants to bloom in the spring. It signals to me the end of winter, and if winter is waning, can butterflies be far behind? A wetland denizen, Skunk Cabbage occurs in soils with high organic content and ground water seeping at or near the surface. It is far more common in northern Indiana, but there are a few places near where we live in southern Indiana where it can be found. Sandy and I visited one of those places—in western Owen County—last Saturday. The gradual warming over the past several days combined with Saturday’s unseasonably warm 72-degree temperature and sunny skies, made us optimistic that some might be up and beginning to bloom. As we walked through the woods towards the seep, we began to notice tips of leaves and spathes beginning to push up through the dead leaves of the forest floor. When we arrived at the main seep, Sandy soon found a few plants whose spathes had pushed all the way up and were beginning to bloom. We were certainly early—there were only a few plants actually blooming—but within a few weeks the entire area around the seeps will probably be littered with hundreds of Skunk Cabbage hoods. Spring is definitely on the way!
Skunk Cabbage (Symplocarpus foetidus) is a member of the Arum (Araceae) family, which also includes the much more common Jack-in-the-Pulpit, a wildflower of our woodlands. Most Arums, including Skunk Cabbage, have very small flowers located on a tubular or globular-shaped spadix that is partially enclosed by a hood, or spathe. The spathes of Skunk Cabbage are about 3 to 5 inches tall and a beautiful mottled reddish-brown and green. As the spathe emerges from the ground and spreads open, the flowers begin to open on the spadix. The flowers smell faintly of carrion (or skunk, or garlic, or a combination of all three, depending on your nose). They are pollinated by a number of insects attracted to carrion and rotting vegetation, including Flesh Flies (Sarcophagidae) and Blow Flies (Calliphoridae). As the bloom season progresses, Skunk Cabbage is also pollinated by early-flying Honey Bees (Apis mellifera).
Skunk Cabbage is an extraordinary plant. The mottled spathe and later, their large leaves, give them a unique tropical look (the Arums are indeed a tropical family—Philodendrons, the popular house plants, and Caladiums, the summer annual with brightly colored leaves—are also Arums), but what truly sets Skunk Cabbage apart is its ability to produce heat. Many Arums produce heat when they bloom, but this is usually, especially among tropical Arums, a brief period of a day or two. Skunk Cabbage maintains its heat production during the plant’s comparatively lengthy blooming period of a few weeks or more. As the spathe Is pushed up, the plant begins to produce heat within the spathe—and maintains it at a near constant and very cozy 72 degrees. The heat inside the spathe is sufficient to melt snow and ice around the spathe, allowing the plant to begin blooming in late winter or very early spring, even if there is snow still on the ground. The “tropical” environment created within the spathe protects the flowers from inclement weather, and the flowers are further protected by the fleshy quality of the spathe, which is thicker than other Arums, and contain numerous air spaces—similar to styrofoam—which help insulate the spadix and its delicate flowers.
The remarkable heat output of Skunk Cabbage is achieved through respiration by its spadix. As oxygen is consumed during respiration, nutrients are broken down within the plant (probably the starches stored in the roots) and heat is given off. To maintain the near constant temperature within the spathe, the rate of respiration and oxygen consumption increases as the air temperature outside the spathe falls. This fluctuation in respiration is similar to a warm-blooded animal which maintains its interior at a near constant temperature regardless of the outside temperature. In an article published in Natural History, Roger Knutson noted that the Skunk Cabbage’s rate of respiration was nearly equal to a small shrew or hummingbird and that the plant was ‘behaving more like a skunk than a cabbage.’ [To learn more about this remarkable plant and its heat production, see Roger M. Knutson, 1979. “Plants in Heat.” Natural History, 88(3): 42-47, and Craig Holdredge, 2000. “Skunk Cabbage (Symplocarpus foetidus).” In Context, 4(12-18)].
As the flowers age, the leaves, which first appear as a spear-point adjacent to the spathe, unfold into large, cabbage-like leaves up to 2 feet long. The spathe withers away beneath the leaves, and the spadix and pollinated flowers form a blackened, brain-like mass containing the seeds. This mass decomposes and releases the seeds close to the parent plant. In August or September, the leaves wither away and reveal the tips of next spring’s spathes just above the ground, waiting for the coming of spring. On October 31, 1857, Henry David Thoreau observed these waiting buds and wrote in his Journal:
“If you are afflicted with melancholy at this season, go to the swamp and see the brave spears of skunk cabbage buds already advanced toward a new year. Their gravestones are not bespoken yet. Who shall be sexton to them? Is it the winter of their discontent? Do they seem to have lain down to die, despairing of skunk cabbage-dom? “Up & at ‘em,” “Give it to ‘em,” “Excelsior,” “Put it through”—these are their mottoes. Mortal human creatures must take a little respite in this fall of the year; their spirits do flag a little. There is a little questioning of destiny, and thinking to go like cowards to where the “weary shall be at rest.” But not so with the skunk-cabbage. Its withered leaves fall and are transfixed by a rising bud. Winter and death are ignored; the circle of life is complete. Are these false prophets? Is it a lie or a vain boast underneath the skunk-cabbage bud pushing it upward and lifting the dead leaves with it? They rest with spears advanced; they rest to shoot! I say it is good for me to be here, slumping in the mud, a trap covered with withered leaves. See those green cabbage buds lifting the dry leaves in that watery and muddy place. There is no can’t nor cant to them. They see over the brow of winter’s hill. They see another summer ahead.”