The Carlisle Mosquito Online

Friday, May 14, 2010


Field Horsetail


Before Brillo, there were Horsetails. (Photo by Kay Fairweather)

Horsetails are the only surviving members of an ancient order of plants, the Equisetales. They are older even than the Ginkgo tree which is often referred to as a living fossil. Ginkgo fossils date back to the Permian period (around 300 to 250 million years ago) while Horsetail fossils date to the Carboniferous period (around 360 – 300 million years ago). Horsetail and Ginkgo, along with ferns and clubmosses, existed prior to the flowering plants which didn’t start to appear until the beginning of the Jurassic period around 200 million years ago. Back in Paleozoic times, the heyday of the Horsetails, there were forests of tall horsetail trees. Of 30 species throughout the world today, the tallest is in South America and reaches about 32 feet.

Name: Field Horsetail is Equisetum arvense and is the most common of the ten Horsetail species that occur in the northeastern U.S. Other names for Horsetails are scouring rush, horse pipes, joint grass, bottlebrush, foxtail, pinetop, and snake grass. The genus name is from the Latin “equus” meaning horse and “seta” meaning bristle. The species name is from the Latin “arvum” meaning field.

Where seen: There is a large patch of Horsetail along the edge of the Foss Farm field where it abuts the Great Meadows National Wildlife Refuge. The patch is many yards long and extends several feet back into the woods. There is also a long narrow strip alongside one of the ditches at the Cranberry Bog. Field Horsetail can grow just about anywhere but prefers damp, sandy places with partial shade.

Distinguishing characteristics: Field Horsetail, like other Horsetails, has two forms; the fertile one which bears a “cone” or strobilus, and the sterile one. At Foss Farm I found mostly the sterile form. Each stem is no more than two-feet tall, is longitudinally grooved, and hollow. It has distinctive nodes which give it a kind of bamboo appearance. At each node there is a little whorl of teeth that clasp the stem. The tiny scale-like teeth are actually the only leaves on the plant. The thin green things that also grow in whorls and look like long skinny leaves are branches. A close look will show they have their own nodes and little whorls of teeth. Stems and branches are both capable of photosynthesis. The fertile form has a shorter stem, only about six inches long, a single spore-bearing strobilus at the tip, and is very short-lived. This stem which has no chlorophyll, is flesh colored,

Life cycle: Each tiny spore has an outer coat that splits into four strips which stay attached at a single point. These strips are highly responsive to moisture. The spores are dispersed as the strips twist and curl in reaction to the humidity level, but the spores don’t fly off alone. The strips allow them to latch onto other spores thereby increasing the chance they will land in proximity to others of their kind. This is important because the spores germinate into tiny male or female plants (gametophytes) which need one another to create the fertilized egg which will grow into a new horsetail plant (sporophyte). Gametophyte development is relatively rare. Horsetails spread mostly by asexual reproduction from their creeping underground rhizomes.

Uses: Horsetails stems have a high amount of silica. If you fold a stem or two into a little bunch you can use it as an abrasive. Pioneers, Native Americans and campers are reputed to have used horsetail to polish objects and to scour cooking pots, leading to the common name of Scouring Rush. (I have a small scouring animal who rushes to clean any pan that goes on the floor. This suits us both better than harvesting Horsetail.)

As a source of food for animals, its greatest fan seems to be the grizzly bear. In Yellowstone, it ranked in the top ten summer food items consumed by grizzlies. It can be toxic to horses where it acts as a scouring agent of a different kind, and large amounts can be fatal. The plant has played many roles in folk medicine including external application to cuts and sores (it has some antibiotic properties) and internally as a diuretic. Horsetail yields a dye and has been used to color clothing and porcupine quills.

References: Peterson Field Guide to Ferns by Boughton Cobb; Reader’s Digest Magic and Medicine of Plants; US Forest Service website at

Submissions and ideas for the Biodiversity Corner are encouraged on any species that occurs in the wild and was seen in Carlisle. Send a note, a photo, or the whole column to If you have a mystery species, send that too.∆

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