Every morning when I brush my teeth, I peer out of our bathroom window near Waterloo, Belgium, to admire our bushy Senecio Inaequidens (SI for short); I had heard it’s controversial, but until now I knew not why! An attractive plant, sporting dozens of golden blooms from May to December, SI is commonly called South African ragwort, because it hails from the northern part of South Africa at altitudes of 1,400 to 2,800 meters. Frost-tolerant and sun-loving, SI is especially primed to continue its northeastern migration as rising climes fuel its reproductive success. Apparently, each little plant can produce 29,000 achenes, tiny seeds carried by wind and pollinated by insects. Seeds lying dormant in the soil can survive thirty to forty years. Since the 1970s, a combination of westerly winds originating in Liège have dispersed SI further eastward, along railways and highways into Germany. So long as sunlight is plentiful, it thrives in gravelly or sandy soil, growing alongside herbaceous vegetation and among young shrubs, though never in dense thickets nor near shade trees.

Once again, Germans have good reason to blame Belgians for this scourge. SI was first noticed in Belgium in 1922, so it is a true neophyte, whereas most invasive plants are archaeophytes (they arrived before 1500). Traveling from South Africa to Mazamet (France) in bales of sheep’s wool, SI seeds later invaded Liège, Calais, Bremen, and Verona—all cities hosting wool-processing facilities used for carding or trade. Working its way across Europe, SI landed in Scotland (1928), France (1934), the Netherlands (1939), Italy (1947), Denmark (1988), Berlin (1993), and, to everyone’s surprise, eventually Norway (1995).

The reason why some consider SI a problem is that it is poisonous to neighboring plants and some animals. Although only one caterpillar eats it, sixty-two phytophagous insects have been observed feeding on it in Berlin. Few, however, consider it an actual threat to indigenous species. Elsewhere, SI has been known to infiltrate wheat fields and pastures, thus risking human exposure to toxic cereal and milk consumption. It has been known to poison horses. Resistant to herbicides, SI is encouraged by mowing, leading seeds to be spread farther. Luckily, employing biocontrol with aphids and beetles seems to be effective. I propose here that the reason why SI wasn’t known in Berlin until 1993, but then suddenly became ubiquitous, is that so many buildings were knocked down after the wall fell, thus reducing shade and creating plenty of ruderal sites where SI could take root.

Unless SI is found growing in fields hosting cereals, cows, or horses, I recommend that human beings learn to appreciate this lovely flowering bush. Rather than rip out every invasive species, we ought to accept that ecosystems are complex. Moreover, any goal toward achieving biodiversity ought to include invasive species, whose disappearance at this point might result in unintended consequences, exacerbating species loss. Life is in a precarious balance, even if such relationships are not ideal. Even though the French call weeds mauvais herbes, not all weeds are necessarily bad, and most serve irreplaceable functions. For example, the ubiquitous dandelions are not only an edible resource, but their deep roots prevent soil erosion.