If you were wading along the paths of Marblehead’s open spaces in your hip-boots 350 million years ago, you’d be enjoying the shade of huge horsetail trees along the path.  Look up!  The horsetails during this period of earth’s history were around 90 feet tall.  They were so common that they were considered the most frequent plants in the forest understory around the world.

Fast forward to today – without the hip-boots – and you won’t find forests of towering horsetails along the trails now.  From being one of the most prevalent plants on earth, horsetails have declined to be only one genus of about 20 species, although they do grow in large quantities on every continent except Antarctica.

Horsetails, also called equisetums, don’t look like any other plants around.  Field equisetums, the most common kind that we see around Marblehead, grow about 5-24 inches tall and have hollow, jointed, ridged stems, with black points above white bands around each node.  These white bands are the leaves that fuse together.  The nodes also send out odd fluffy-looking soft green bristles, which are actually branches.  Both stem and branches – but not the leaves – produce food for the plant through photosynthesis.

Horsetails skip the flower-and-seed business that most plants invest so much time and energy in.  Each horsetail plant is topped with a cone-shaped tip.  The earliest horsetails to come up in spring are grey or tan, about 6 inches tall, and produce fertile spores in the top cones. Later in the season the more common green horsetails appear, each topped with a cone which produces sterile spores. Fertile cones have unique structures to help spread spores.  There are 4 little ribbon-like wings stuck to the bottom of each spore.   In wet weather the ribbons pick up moisture, twist around the spore, and stick the spores close to the cone.  In dry weather, the ribbons dry and uncurl, the spores dry, and the wind has a better chance of blowing dry spores to their next home.

Spores are not the main way horsetails spread however, since they don’t usually find enough moisture to germinate and grow. Horsetails mainly spread through their rhizomes underground, which are tough and grow very deep.  How deep?  Ohio Weedguide says field horsetail rhizomes can grow as deep as 20 feet and horizontally as long as 330 feet.  If even a fragment of rhizome is left after digging out the plant, it will grow again.  This, along with horsetails’ resistance to herbicides that kill seed-producing weeds and their poisonous effect on cows and horses, lead horsetails to be considered a noxious weed in Australia and Oregon, and an “unwanted organism” in New Zealand.

Horsetails were not always considered a nuisance.  They have been used throughout history in Europe and Asia to scour and polish metals.  In Japan, horsetails were boiled then dried, and used in the final sanding for woodworking since they are finer than sandpapers. Both polishing and sanding are possible since silicates make up more than 50% of the plants’ dry material. Earlier cultures also used horsetails as a diuretic, to help heal joint diseases, urinary tract disorders, gout, and hemorrhage.  Current medicine has not been able to substantiate any of these claims.

One more interesting fact about horsetails, for math and science buffs: John Napier got interested in the pattern of spacing between horsetail stem nodes (spacing decreases as you get closer to the top) and used it as the basis for inventing logarithms in 1614.

Look along the trails in Steer Swamp for horsetail colonies near swampy areas.