It may have escaped your notice, but spring has begun. Skunk cabbages officially kicked off the vernal season two or three weeks ago. Spring is also under way for the 70 sandhill cranes that passed through Calumet Park a week ago. And it is under way for killdeer, redwings, and grackles. The juncos that spent the winter here have begun to sing as they prepare to return to their breeding grounds in the north woods.
If you pay attention spring in Chicago can drive you crazy. Forget about temperature and windchill; just think about how long it takes for the whole drama to unfold. This is a four-month season. It is already under way and won't be over until the middle of June. In the meantime we shiver and wait for the first field sparrow and the first spring beauty. And way off in the future--almost two months from now--the wood warblers. The trees will open when the warblers arrive. If it isn't too cold.
We are now in the early--or duck--phase of the drama. It's a good time to get a real feel for the effects of windchill by standing on the lakefront for long periods scanning the waves for redheads and shovelers and clouds of mergansers.
The sight of a skunk cabbage can help you through these times. On days when everything else in the landscape is lying low, skunk cabbages are in full and glorious bloom, attracting pollinating flies and carrion beetles to their flowers. They can bloom in February because they generate their own heat. The outside temperature can be 10 degrees Fahrenheit, or 30 degrees, or 50 degrees. Inside the purple cowl that protects the flower cluster it's always a pleasant 72.
Skunk cabbages are aroids, members of the Araceae, a mostly tropical family with some unusual habits. The flowering parts of aroids consist of a cowl, called a spathe, that shelters a generally long, slender, and very phallic spadix. Many small flowers grow on the spadix. The Sumatran Amorphophallus titanum has a spadix up to six feet tall. Like the skunk cabbage, it caters to insects with low tastes. To attract them, it emits an almost overpowering odor that has been described as a combination of burnt sugar and rotting fish. Some of the volatile chemicals released by various aroids have been analyzed and named. The names are descriptive: skatole, for example, or--my own favorite--cadaverine.
Jack-in-the-pulpit is the only other aroid native to our part of the world. The pulpit is the spathe; Jack is the spadix. The inner side of the top of the spathe is often brownish purple in our local jack-in-the-pulpits, and the spathes of skunk cabbages are a similar hue. Brownish purple is a color that lures insects that feed on decay.
Jack-in-the-pulpits undergo frequent sex changes. Small plants produce male flowers, but if a male plant enjoys a really good year it will produce female flowers the following spring. After a bad year it will go back to being male. The energy demands on females are much greater than they are on males. Males produce only pollen. Females produce seeds and fruits as well. It takes a big, healthy plant with lots of stored energy to take on the task of being female.
Jack-in-the-pulpit flowers are pollinated by tiny fungus gnats. The gnats fly into the male flowers, gather some pollen, and then discover they are trapped. The walls of the spathe are so smooth they can't climb them, and the chamber is so small they can't fly. The only way out is through a small opening at the bottom of the spathe.
If the gnats find their way out and travel to a female flower (jill-in-the-pulpit), they deposit their pollen--and then discover that female flowers have no exit. By the end of the flowering season female flowers are half full of gnat corpses.
This system of pollination has serious drawbacks. The gnats get no reward for pollinating the flowers. They are apparently lured into the flowers by scents and colors that remind them of the sort of fungi they prefer for egg-laying sites. Any gnat that completes an actual pollen transfer dies without offspring. The only gnats that successfully reproduce are those that stay away from jack-in-the-pulpits. In other words, jack-in-the-pulpit plants are exerting selection pressure on these essential fungus gnats, the effect of which is to reduce the number of gnats available for pollination. Many jack-in-the-pulpit flowers produce few seeds, and it could be that generations of murdered pollinators are coming back to haunt them.
The environment in a skunk cabbage is far more benign. A considerable assortment of creatures make use of the warmth inside the spathe. Honeybees don't fly well when the air temperature gets below about 65 degrees. But they have been observed visiting skunk cabbages when temperatures were as low as 42 degrees. Their strategy is to sit on the spadix--where the heat is--until they are warm enough to make the flight to the next plant.
Predators live in the spathe too. At least one species of spider apparently uses the spathe as a place to meet members of the opposite sex. This spider may get the jump on other species by mating in this uniquely warm place in a very cold environment.
Skunk cabbages generate heat the same way we do: by burning large amounts of food. There are other plants--including other aroids--that respire fast enough to raise their temperature, but these high-energy states are maintained for only a few hours. In the skunk cabbage these warm times can go on for as long as a month. At peak levels the spadix is consuming oxygen and burning food at about the same rate as a shrew or a hummingbird. At that rate the plant can sustain temperatures as much as 60 degrees above the surrounding air. The heat is sufficient to melt snow around the plant and to thaw frozen ground.
Pack snow or ice around the spathe, and the temperature inside will start to drop. The decline will continue for about an hour before rising to earlier levels. The time lag probably represents the time it takes a hormonelike chemical to diffuse through the plant and signal the roots to pump more fuel to the spadix. What we have here is a warm-blooded plant, a creature with its own furnace and its own thermostat.
The massive amounts of energy needed to fuel this unique creature are stored in a thick underground stem that may be a foot long and several inches thick. Hundreds of smaller roots grow down into the soil from the upper part of this underground stem. Each fall these smaller roots shorten in unison, pulling the plant down into the soil. The downward movement is about equal to the annual increase in the length of the underground stem, perhaps half an inch. It can keep growing forever and always stay underground. The skunk cabbage is a warm-blooded plant that moves.
The number of calories in that thick underground stem might make the skunk cabbage worth eating. Other aroids--such as the taro root, widely eaten in Polynesia--do provide food for humans. However, there are problems, starting with that foul odor. An uninjured skunk cabbage actually has a faintly sweet odor. But if you injure the plant an odor described as a disgusting combination of skunk, rotting meat, and garlic will fill the air. This would not improve your appetite.
And then there are those crystals of calcium oxalate in the plant juice. Most aroids contain these tiny sharp crystals called raphides. If you eat them you get an intense burning sensation inside your mouth. Dieffenbachia, the common houseplant, is an aroid. One of its common names is dumbcane. If you lick the cut-off end of a dieffenbachia stem, the raphides of calcium oxalate will cause your tongue to swell enough to prevent you from talking. The effect can last for days and in some cases the swelling gets so large it cuts off the breathing passages and you die.
According to some sources, you can render skunk cabbage odorless and fairly harmless by boiling it in several changes of water. Or you can take the Menominee approach and use small amounts--smell and all--as a seasoning. Or you can forget the gastronomic possibilities of the plant and just enjoy the sight of something brownish purple growing in the cold days of early Chicago springtime.