A stinky, ancient, mysterious plant…and a bear’s spring laxative!

by Ellie Nowels

Skunk cabbage  (Symplocarpus foetidus), also known as Clumpfoot Cabbage, Swamp Lantern, or Polecat Weed is one of the earliest flowers to emerge in the spring. Skunk Cabbage is a very ancient plant, and may have existed in near its present form as far back as the Cretaceous Period (between 145.5 and 65.5 million years ago).

This perennial herb appears as early as mid or late February, often emerging in damp wooded areas even while surrounded by standing snow.

Skunk cabbage in the snow

It can do this because it belongs to a small group of plants that raise their temperature higher than the surrounding air. The process is called thermogenesis, and it involves mitochondria generating heat as part of cellular respiration. Fueled by energy stored in the plant’s modified underground stem (called a rhizome), skunk cabbage can maintain temperatures of over 50 degrees within the spathe (the leaflike bract that encloses the flower cluster or spadix) even as external air temperatures drop below freezing. It produces warmth over a period of 12-14 days, remaining on average 36° F above the outside air temperature, day or night.

Why does skunk cabbage produce heat? Despite several studies of this phenomenon, the answer is unclear. Production of heat may be necessary to allow skunk cabbage to grow and flower in a rather inhospitable environment. By flowering well before most other plants, skunk cabbage may be able to take advantage of any insects that are active at this time of year, with the heat performing the additional function of spreading the plant’s pungent aroma, attracting insect pollinators. The smell has been compared to rotting flesh, and the mottled purple spathe looks a bit like meat. The combination attracts carrion flies which are among the very few pollinators in early spring when the skunk cabbage first emerges. (author’s note: I’ve visited skunk cabbage patches several times and barely notice any smell. But I’m not a carrion fly).

Skunk cabbage spathe showing the spadix (flower cluster)

Reproduction
Skunk cabbage reproduces by seed, not by horizontal rhizomes as other members of the Arum family. Pollinators are attracted to the smell and enter the spathe, where they are drawn to the region of female flowers at the bottom to fertilize them. Only after this occurs do the male flowers near the top open to drop pollen on the insects, which then spread it to other plants; it’s all timed to prevent self-pollination.

Skunk cabbage flowers are all female when the spathe first opens. These later become pollen-producing male flowers, with flowers at the top of the spadix transitioning first. Heat production peaks during the female phase, declining as the flowers age and begin to produce pollen.

How pollination happens is still a bit of a mystery. Some sources say that while flies have been documented at skunk cabbage flowers, it’s not clear if they successfully pollinate the plants. While honey bees visit, it’s considered unlikely that they act as effective pollinators, since they tend not to visit skunk cabbage’s nectarless female flowers and may not even make contact with the spadix itself, instead collecting pollen that has fallen to the base of the spathe. According to Illinois Wildflowers website, “The flowers are pollinated by flesh flies (Sarcophagidae), carrion flies (Calliphoridae), and various gnats.”

Medicinal use and a laxative for bears
Skunk cabbage produces the chemical calcium oxalate that is considered toxic and can cause a burning sensation when ingested. However, it was widely used by Native Americans in small doses and after the leaves had been dried sufficiently to reduce the toxicity. They used it as a poultice to heal skin wounds and inhaled the vapors from crushed leaves to cure headaches. Early colonists considered it a contraceptive, believing that one tablespoon three times a day for three weeks would cause sterility. It was listed in the United States Pharmacopoeia from 1820 to 1882 and was used as a treatment for a wide variety of ailments including asthma, epilepsy, spasmodic coughs, and rheumatism.

Because of the toxic calcium oxalate, it’s generally considered inedible. However, after they emerge from hibernation in the spring, hungry black bears and snapping turtles will eat the foliage. Black bears may consume large quantities of the buds and leaves when other food is low; the plant is sometimes known as Bearweed because of this. It also provides an important laxative function that helps bears “become unplugged” in the spring.

Skunk cabbage spathe showing the spadix flower cluster

Fruit
When skunk cabbage’s flowers have been pollinated, the fruits begin to grow. The flower head swells and develops into a fruit head. The spathe withers and dies, and the stalk that carries the fruit head elongates, growing along the surface of the ground. By mid-June the fruit heads are roundish balls, about two inches in diameter. They usually have the deep, wine-red color of the spathe. The fruit heads house numerous round, berry-like fruits, each containing one seed. In August the fruit head falls apart. The fruits lie on the ground — to be eaten, to decompose, or to germinate (either in the fall or next spring).

Structure
The skunk cabbage has a well-established root system that consists of a vertical rhizome that can extend up to 2 feet into the ground with a mass of roots radiating in all directions. The roots are unusual in that they have circumferential ridges at regular intervals that contract to pull the plant down into the ground every spring so that the stems and leaves stay at ground level. The root structures are virtually indestructible, and can be hundreds of years old.

Skunk cabbage leaves

When the spathe emerges out of the ground, there is often the tip of a large bud next to it, sticking an inch or two out of the ground. Only when the spathe slowly begins to wilt does this tightly-packed bud of leaves begin to grow. The bright green leaves unfold in a spiraling pattern. Each leaf is rolled in upon itself and at the same time enwraps the next leaf. The largest leaves reach three, occasionally four feet in length, peaking in mid-May. The leaf stalks are thick, but also easy to crush. By mid-June  the leaves of skunk cabbage begin to decay. They don’t dry up and fall onto the ground to become part of the leaf litter; instead the leaves get small holes in them, begin to hang down, and parts turn black and somewhat slimy. Essentially the leaves dissolve and are gone by late July or early August. Since the leaves are mostly water, there are no woody fibers to leave on the ground.

The rootstock or rhizome, a thick roundish stem, still remains; and it’s very difficult to dig a plant out of the ground. There is no taproot. The roots have virtually no branches until near their tips, where they turn into many small, fibrous rootlets. They are now storing starch for next year’s heat-generating emergence in early spring.

Sources:

https://www.natureinstitute.org/article/craig-holdrege/skunk-cabbage

https://hikersnotebook.blog/flora/other-plants/skunk-cabbage/

https://jimmccormac.blogspot.com/search/label/skunk-cabbage

https://www.nwf.org/Educational-Resources/Wildlife-Guide/Plants-and-Fungi/Skunk-Cabbage

https://www.marylandbiodiversity.com/species/1660

https://sites.tufts.edu/pollinators/2020/02/turning-up-the-heat-strange-and-stinky-skunk-cabbage/

https://www.facebook.com/watch?v=1849679595835017