Our Window on Nature

This country is not only peopled by immigrants, but it’s vegetated by them as well. A high percentage of the plants you see when traveling across the North American continent are actually non-natives.

The seeds of these first exotics, as they’re called, arrived right along with the explorers and colonists. Some were intentional imports; others weren’t. Grasses such as timothy, crabgrass, and ryegrass were used to feed cattle. Wild parsley and chickory were used for food, while foxglove, coltsfoot, and tansy served medicinal purposes. Other plants were brought for their beauty, in an effort to ease the loneliness of life in a new land.

A couple of centuries later, botanist J.M. Fogg found that 14 percent of the plants listed in Gray’s Manual of Botany - more than 1,000 species in all - were introduced.

Not all of these non-native species came as invited guests, of course. Many crossed the ocean attached to the clothes of the colonists or to the fur of their animals. In his book North With The Spring, naturalist Edwin Way Teale points out an example of how it can happen.

Botanists wondered why several European plants should be found only in two widely separated areas on the east and west coasts of South America. The explanation lay in the habit of early colonists sailing to Australia with their sheep. “They stopped (on the east coast) to let the animals graze before rounding Cape Horn, then stopped again to pasture them on the west coast before starting the long voyage over the Pacific.” The sheep left behind a legacy of seeds that had dropped out of their woolly coats. And since weeds they’d been in the old country, weeds they became in the new.

An even greater source of weed species in America was the tons and tons of soil carried in British ships and dumped along east coast harbors. It wasn’t that early settlers needed English soil for crops and gardens, but that ship owners used dirt as ballast. Waste soil filled the ship’s holds on the trip over; fine southern cotton filled them on the trip back. From that dirt ballast, hundreds of new plant species were introduced into this country. Mighty pests from little seeds grow.

Since by definition a weed is any plant growing where you wish it weren’t, all introduced species probably qualify as weeds somewhere - but many also provide beauty, in or out of the flower bed. Many of the flowers and herbs that escaped over the garden wall naturalized among the native wildflowers without crowding out their hosts. Some became eyesores and a few real budgetbusters. Before we go into individual species, let’s consider how the offspring of these immigrant seeds spread clear across the continent.

Man is the primary reason. As early settlers cleared the forest for fields, they created what is called “disturbed ground” - an arena where sun-loving weeds and domestic seeds could compete favorably with native species. Nature played a role in clearing land, due to windstorms, fire, and flood, but man was ever the major factor.

Once they had a toehold, the exotics were fruitful, multiplied, and went out to conquer the earth. Here, too, man played a role, with the aid of the wind.

Some species have evolved special adaptations that allow their seeds to take advantage of the force of winds. Just cast your memory back to your childhood fascination with dandelions (a non-native to these shores). Each seed carries its own private parachute. Nature provides the means, while man provides the open spaces in which seeds can collect.

The artificial winds of railroads and highways do their part in seed dispersal. Clouds of seeds swirl down the right-of-way, energized by each passing truck or railroad car. Every season more seeds are carried into the interior, until they reach every square inch of hospitable soil. The country has never had as uniform a plant life as it has now, all due to the homogenizing effect of man and his methods of high-speed transportation.

Is this all to the bad or to the good? That depends upon the plant. The foxglove, the ox-eye daisy, the day lily, and the daffodil all readily escape from cultivation and slip off into the countryside. Can anyone say we aren’t better off for their presence? But what if the plants spread into an area where endangered native species are having difficulty surviving? Are we willing to pay the price of their beauty?

And then there is the common mullein. Today you see its golden paintbrush flower head from Atlantic shores to California’s Sacramento Valley. The colonists brought it over for practical reasons, as a part of their pharmacopeia. Pioneers couldn’t run down to the corner drugstore for cough drops, so they drank mullein tea. Then they bound up their sore throats with the woolly leaves. Considering the scratchy texture of those leaves, we suspect that they got well mostly in self-defense. Today’s cold sufferers don’t need mullein, but the plant can never be eradicated.

Japanese honeysuckle certainly qualifies as a beautiful plant. It’s also the bane of farmers, hayfever sufferers, and people concerned with its spread through areas that once teemed with natural vegetation. How can well-mannered natives compete with a vine capable of traveling more than 45 feet in only one growing season?

And what about kudzu, a vine capable of growing a foot a day? The U.S. Department of Agriculture has to share the blame for this one, since they encouraged southern farmers to plant it in the first place. Today it’s out of control - invading farms, surrounding trees, devouring fences and barns like some nightmare from a science fiction movie.

Even trees become pestiferous. The tree-that-grows-in-Brooklyn, alias stinkweed, alias tree-of-heaven, grows happily among tenements and urban litter. It does even better in the country. Nice in the city - nasty everywhere else.

Clearly our exotic plant life is a mixed blessing. So we might as well go on enjoying the beauty of the wildflowers and cursing the invasiveness of the pests - because there’s certainly no relief in sight. These foreign flora, like the humans that brought them and facilitated their spread, are quite definitely on this continent to stay.