I enjoy walking (almost every day) in the forests and fields near Hoenheim (Hœnheim), France, which is near Strasbourg. These forests and fields are in the Rhine River plain, not in the mountains. These areas have been disturbed by human civilization for thousands of years.
But as I walk through them, I have a feeling that I have already been here. That is because the forests of Alsace have many of the same herbaceous species as North America—that is to say, weeds. Hundreds of years of commerce and industry have led to a nearly uniform set of weedy plants in the two places. You probably already knew that, but I will give you some specific examples—as a matter of fact, sixty-one of them.
The trees are usually the same genera (oaks, poplars, willows, etc.) but not the same species. For example, cottonwoods (Populus deltoides) are along nearly all rivers in eastern North America, while in Europe it is Populus nigra, the black poplar. America and France both have willows along the rivers, but not the same species—for example, the gray willow (Salix cinerea) is found here but not in America. Some of the “weedy” trees are the same (such as tree of heaven, Ailanthus altissima, and the empress tree, Paulownia tomentosa) but this is unusual.
The most common pattern is for weedy species to originate in the Old World and then invade America. But there are some notable exceptions. The ragweeds (Ambrosia) and amaranth (Amaranthus) evolved in America before invading Europe. The best tree example is the black locust tree (Robinia pseudoacacia) which the French call robinier. Unlike most weedy species, this one evolved in America and then invaded Europe, escaping from the garden of the American collection of the French botanist Jean Robin.
Another plant that is really abundant in our forests, especially beside the Ill River, is Parthenocissus quinquefolia, or Virginia creeper. As the name might suggest, it is native to the eastern deciduous forests of North America. But it is, in some places in France, the dominant understory plant.
But there is one understory vine I have never seen in France, nor heard that it has gone wild in France: Toxicodendron radicans, the poison ivy. One website said that the “sumac vénéneux” has been found in a couple of places in France. But it stands nearly alone as an American weed that has not spread in Europe. We can walk with confidence through the undergrowth, being cautious of the abundant nettles (our own species) but not fearing poison ivy.
Occasionally, some abundant herbaceous species in France (such as the nettles just mentioned) are different from their relatives in America; for example, the clematis known as old-man’s-beard, or clématite des haies, is different from the wild species of clematis I saw in Oklahoma. But my list includes 59 species of weeds (plus two trees) found in both France and America. I made a list and scanned it so I could include it in this blog essay if you would like to look at it.
No wonder I felt right at home when I started walking in the woods after moving to France.
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