“We can in fact only define a weed, mutatis mutandis, in terms of the well-known definition of dirt – as matter out of place. What we call a weed is in fact merely a plant growing where we do not want it.”
-E.J. Salisbury, The Living Garden (1935)
“What is a weed? A plant whose virtues have not yet been discovered.”
-Ralph Waldo Emerson, Fortune of the Republic (1878)
Ah yes, the lowly horsetail. A weed, some say, an eyesore proliferating in roadside ditches and untended yards. Who hasn’t seen this Plain Jane of a plant, cropping up alongside urban trails or thrust inexorably through the asphalt? Who hasn’t yielded to that primal urge, upon finding a stand of horsetail in the forest, to grab a stick and whack their brittle stems to bits? It’s only natural. People love to hate the horsetail. It’s an interesting antipathy, though—one that makes less sense the more one scrutinizes it.
Horsetails are an ancient lineage. The twenty or so extant species constitute the only living genus of Equisetopsida, a diverse class of plants dominant during the Carboniferous Period, 350 million years ago. Characterized by having roots, stems, and leaves but no flowers or seeds, these plants, in their myriad forms, filled out entire forests throughout the Paleozoic. Some, like Calamites, grew to a hundred feet or more. Others such as Sphenophyllum were slender and vine-like. Horsetails and their ilk—along with ferns and club mosses—reached their peak during the warm, swampy eons of the Carboniferous, but as the climate 290 million years ago increasingly dried out, these wet-adapted plants died off en masse. Their remains, molded by heat, pressure, and geologic time, became the coal seams and oil fields we humans are so intractably reliant upon today. It’s through the largesse of those lowly plants that humans have lived so lavishly. They died for our whims. And of the Equisetopsida, horsetails are all that’s left.
Good news is, they’re everywhere. Horsetails grow on every continent except Antarctica, ranging in height from a foot or so for the temperate species to more than twenty feet for the giant horsetail of Central and South America. They reproduce sexually with spores or asexually through rhizomes underground—the former working better in swampy areas, the latter best suited for terrestrial expansion. Horsetails have hollow, segmented stalks ringed by small, chlorophyll-free leaves; the stalks themselves are photosynthetic, and in some species sprout whorls of thin branches to better capture sunlight. These stalks are ridged and hardened with silica—the common name “scourbrush” refers to this quality, as, historically, people from numerous cultures have used horsetail like a biodegradable Brillo pad, cleaning dishes, scrubbing tins and even polishing wood.
Horsetails couldn’t have made it all this way if they weren’t hardy little things. Herbicides that prohibit leaf growth have little effect on them, because the leaves don’t contribute to growth. So-called “contact” herbicides also don’t work, because although the stalks may die away, the perennial rhizomes lie safe beneath the soil. Attempts to rototill tend to chop up and redistribute these rhizomes, whereupon each piece puts down new roots and sprouts again. One study in Quebec found that even after hoeing a plot sixteen consecutive times, the horsetail rebounded with equal vigor. It is indomitable, this plant, simply ineradicable. One gets the sense that to take on horsetail is to engage in a losing battle. Nature itself doesn’t have a handy solution. Most horsetails are toxic to animals when eaten in quantity, though humans can get away with eating tender shoots and the spore-bearing bodies—called strobili—if they’re careful. Like cockroaches and plastic bags and chlorofluorocarbons in the atmosphere, horsetails are in it for the long haul, and will persist even as we scour other life forms from the face of the earth.
So why begrudge them their fortitude? Horsetails are relics, deserving of respect and at least a little humble appreciation. They’ve been on this planet far longer than us—far longer than most species, in fact. And besides, if you can’t beat them, at least try to learn something useful in the process: Even the weeds have stories to tell.