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Horsetail: The Abrasive, Prehistoric Cool Kid

By Kathleen M Hale, Western Reserve Herb Society

horsetail 1Now appearing, ready for its close up, one of The Herb Society of America’s two Notable Native Plants of 2019, and a plant that is a living fossil: horsetail or Equisetum. Sharks get called living fossils a lot. So do marsupials, like possums and wombats. It definitely carries with it a sense of being strange, but cool.

Fossils are the remains or impression of prehistoric organisms preserved in petrified form or as a mold or cast in rock. A “living fossil” is just something that’s really, really old.  And alive, of course. The term was first used in 1859 by Charles Darwin in his “On the Origin of Species.” Living fossils have remained in evolutionary stasis — remaining much the same — since the time of now-petrified critters, long extinct.

Horsetail is the only surviving genus of the class Equisetopsia.  Horsetail might be said to have had its peak back in the late Paleozoic era, when members of its family were prolific.  But its characteristic growth pattern (with the nodes along its shoot growing increasingly close together the closer they grow to the end) inspired the invention of logarithms.  That’s pretty relevant. The 17th century Scottish mathematician John Napier found the pattern suggestive of exponential notation.  I’m not sure he ever said so.  But the claim is frequently made by plant people.

Horsetail, also known as snakeweed, horse bristle, scouring rush or puzzle weed, thrives in zones 3 to 11, grows up to four-feet tall and likes to have its feet wet.  It grows in clusters of segmented reed-like stems, and can regenerate even if cut down to the ground. Horsetail rhizomes spread readily. In fact, Horsetail relies entirely on these rhizomes to propagate, bearing neither flowers nor seeds.  In some places, horsetail grows as a valued aquatic or semiaquatic plant. In other places, like Oregon and New Zealand, it is considered invasive.

horsetail 2

If you find yourself with a patch of horsetail run amok, you can do it in by raising the soil pH.  It is an acid-loving plant, and a little lime should do the trick. Some people try vinegar.  But you know better. It might be best, if you decide to plant horsetail in a swampy part of your garden, to restrain its spread by planting it in a sunken container.

The stem of horsetail is coated with microscopic white silicates.  These have been useful in polishing and smoothing both metal and paper. Horsetails have also been used to clean woodwinds as a reed scraper.

Horsetail has been employed in a number of medicinal preparations, particularly as a diuretic. It is unwise to ingest it.  Horsetail has proven toxic to grazing animals, because of the presence of thiaminase, which can cause thiamin (vitamin B1) deficiency. This can also make it especially dangerous to people with a thiamin deficiency, a common problem for those with alcoholism. Since horsetail also contains trace amounts of nicotine, it can trigger a reaction for those sensitive to nicotine. There is a persistent belief that horsetail preparations can, when applied topically, help grow hair and nails. But there is no proof of its efficacy.

So venerate horsetail for its age, honor it for its mathematical complexity, and respect its ability to make itself at home in a big way.  But, as always, treat it with respect.