An Aromatic Sauna for Pollinators
In very early spring, the first pollinators emerge when most plants still lie hidden under snow and soil. For such pollinators, plants capable of flowering in the cold are essential for survival. Among these is the skunk cabbage (Symplo-carpus foetidus), a plant native to eastern North America. In the first weeks of March, honey bees can be seen in the park gathering pollen from skunk cabbages poking from snow-covered mud banks bordering Swan Lake.
Skunk cabbage belongs to a small group of extraordinary and fascinating plants capable of thermogenesis – the ability to generate heat. Skunk cabbages produce heat through cellular respiration, breaking down starches stored in their roots. They can generate pockets of heated air around them that average 36 degrees above air temperature. In early spring, skunk cabbages melt snow and thaw soil gathered around their roots. As a result, they are able to emerge and bloom far earlier than most other spring plants.
Skunk cabbage flowers appear before the plant's leaves do. As shown at right, the blossoms of skunk cabbage are striking -- pale yellow flowers arrange themselves in a grid along on a 3-to-6-inch spongey spherical stem known as a spadix. The spadix is greenish yellow or purple and encased within a protective mottled-purple hood called a spathe. Unlike the protective buds of many flowers, the spathes of skunk cabbage never fall away – each plant's flowers remain hidden from the time they first blossom until they fade. The flowers do not produce nectar but are rich in pollen.
Skunk cabbage has a second notable quality – the plant emits an odor described as "a musky scent" by some authorities and as "the rotten smell of carrion" by others. The smell earns the plant the name skunk cabbage. (Its Latin name, Symplocarpus foetidus, means “foul-smelling connected fruits”). The malodorous scent serves to attract early spring pollinators, as does the heated interior of the spathe. (If you stick your finger inside the spathe, you may notice that it is much warmer than the surrounding air.) Bees, flies and stoneflies can be seen disappearing into the cavernous hoods of the spathes, where the insects linger in the aromatic sauna within, raising their body temperatures and partaking of the hidden flowers.
Skunk cabbage’s fetid smell is directed specifically at scavengers responsible for clearing the forest of carrion. These essential members of the food chain, such as the bright green bottle fly shown in the photo strip at right, like the foul odor and enter skunk cabbage spathes to feast -- thus aiding in the plant's pollination. Notably, skunk cabbages also possess the ability to vary their scent, mimicking at least three other odors -- those of turnip, apple and garlic -- in order to attract other pollinators such as honey bees.
After skunk cabbage blooms, the spathes turn dark and wilt, and bright yellow-green leaves emerge. Each new leaf is tightly rolled and holds within its roll another emerging leaf. This method of unfurling may be what earned this plant its French name, Tabac du Diable, or "Devil's Tobacco". The leaves look a little like a rolled cigar.
Skunk cabbage grows in shaded swampy terrain where few other plants flourish. Once the plants' leaves appear, they grow straight upward and then spread outward, in a way a reminiscent of cabbage. By the end of spring, the leaves can be quite large, up to one foot wide and three feet long. The plants grow in vast groups, carpeting the edges of brooks and marshy areas in rich green.
Leafed-out skunk cabbages create a micro-ecosystem in which an astonishingly wide variety of animals flourish -- salamanders, snapping turtles, garter snakes, birds and insects seek refuge amid skunk cabbage leaves. Emerald-green tiger beetles and mosquito-hunting dragonflies, are common denizens of marshy areas where skunk cabbages proliferate in the park.
Despite the appellation “cabbage,” this interesting plant is toxic if ingested. The leaves contain water-insoluble calcium oxalate and can cause a painful burning sensation in the mouth. As a result, few animals feed on skunk cabbages, and the plants' luxurious leaves tend to remain intact and healthy through mid-summer. The plants are not toxic to birds or reptiles, however. Round black seeds from the pollinated flowers fall into the swamp, where they are eaten by small birds and ducks. Snapping turtles occasionally chew on skunk cabbage leaves.
Skunk cabbages have a third extraordinary trait. They have contractile roots, that is, roots that contract after descending into the ground. This pulls the plants' stems earthward, so that they grow downward instead of up. With each passing year, a skunk cabbage reaches more deeply into the soil. From the central rhizome -- which in old plants can be as much as one-foot thick -- numerous roots that look like long, wrinkled fingers extend into the depths.
In July, skunk cabbages seem to disappear abruptly from the park -- the leaves darken and dissolve mysteriously into the muck. The plant, however, continues to grow, its roots fingering downward and anchoring it more deeply in the swamp.
The micro-habitat in which skunk cabbage flourishes is home to diverse species of fauna.
Here, a garter snake searches for frogs in swampy terrain carpeted with skunk cabbage.
A yellow skunk cabbage spadix inside a spathe
PHOTO CREDITS: All photos and text © Copyright 2014-2015 Paula Sharp and Ross Eatman, unless otherwise noted. All rights reserved. If you wish to use any of the photographs here for educational or other purposes, please read permissions page.
REFERENCES: For a comprehensive list of references used in compiling this guide, click here: