Garrett McAuliffe

Nearly 2000 years ago, the Roman naturalist Pliny gave common horsetail its botanical name, Equisetum arvense. But the story of this peculiar plant stretches back hundreds of millions of years, before roots, seeds and leaves evolved, to a time when plants were just beginning to get a feel for life on land.

Imagine these delicate, hollow, green tubes the size of fir trees, reaching heights up to 100 feet in the steamy, oxygen-rich swampland of the late Paleozoic era. Today’s miniature versions, rarely rising above one’s knees, are considered a living fossil—the last relict of a once-dominant family of flora.

As with their ancient ancestors, modern horsetails prefer it damp, clustering along the margins of marshes and stream banks, and looking a bit like asparagus when young. The stems grow in segments, one telescoping into the next, tapering in size as they reach the apex, with needle-like branches arranged in whorls at each segment’s node. Fertile stalks end in a cone-like catkin called a strobilus, which ripens and bursts by midsummer, releasing millions of microscopic green spores into the air. The growth pattern of the stem is so regular that horsetail is said to have inspired Scottish mathematician John Napier’s discovery of logarithms in the 17th century.

Spread across much of the globe, species of horsetail have been used broadly by humans for millennia. These plants seek mineral-rich soils and are uniquely capable of absorbing silicates and certain precious metals into their tissue. With age, stems become coated with coarse strands of silica, a rare element in living things. Traditionally, dried horsetail was used to scour metal, particularly pewter, and polish wooden tools. Natives of the Pacific Northwest ate the young shoots raw, used the plant to make a soft-green dye, and fashioned whistles from its stalks to call on local spirits.

The plant’s ability to absorb minerals also piqued a more acquisitive interest. Miners during the gold rush believed that these plants and others signaled the presence of gold. More recently, Canadian prospectors have sought out gold deposits by analyzing the ashes of burnt horsetail.

As with many plants, horsetail also claims a prime position in the history of medicine. The barren stems have been used as an herbal remedy dating back to ancient Greece—administered as a tincture to heal internal wounds and as a poultice to stop bleeding. Herbalists more recently have trumpeted its use as a diuretic, and for strengthening nails and hair. Today dried horsetail is sold in herb shops and ascribed a number of immunological benefits. Few studies have looked into the medicinal effect in humans, but Europe’s version of the FDA recently ruled that certain species of horsetail have strong antioxidant properties and may inhibit cancer cell growth.

To harvest, pick the tiny green stalks in early spring while the branches still point upwards. Though its texture deters use as a potherb, it can be boiled for a mineral-rich tea—to drink, use as a hair conditioner, or spray in your garden to repel aphids.