By Dr. David Wartinbee, for the Redoubt Reporter
During the first couple weeks of June, most Alaska gardeners are getting their gardens planted. Of course, there is much discussion about when to plant particular species, and it depends on who is doing the planting and the microclimate where one is working.
Despite the variations in planting times, one thing many gardeners in Alaska will agree on is that Equisetum, or horsetail, is the worst weed in the garden.
It seems to come up before anything else and it grows until things are about to freeze. The gardener in my family has muttered many curses on the ancestry of these species while weeding.
Speaking of ancestry, Equisetum plants have been around for hundreds of millions of years, and often show up in Carboniferous period coal deposits. Organisms that have survived that long have evolved some pretty good methods of reproducing and coping with the environment, despite the constant extractions by aggressive gardeners.
Equisetum get its name from Equus (horse) and seta (tail), hence the common name “horsetail.” They are also known as scour rush because they often have minute siliceous bumps on the outer stems. When I was a Boy Scout, we were taught that a bunch of horsetail stems would polish the inside of our cooking kits. You will be surprised just how abrasive the stems can be and how clean a metal pot gets with a little elbow grease.
Some skilled craftspeople still use the stems as a fine abrasive polish because of the minute silicate crystals. Musicians playing reed instruments have long used Equisetum stems for the abrasive qualities in fine-tuning, or honing, their reeds.
There are a variety of different species of Equisetum in Alaska and throughout the world. Each species seems to have its own growth pattern and a variety of structures, like minute leaves or the presence or absence of side branches.
The most common means of reproduction used by Equisetum is vegetative rhizomes. They are 100 times more abundant than the upright stems. They are known to grow more than 6 feet into the soil, which explains why pulling out a stem doesn’t seem to stop the plant’s return. These rhizomes have the ability to work their way through normally inhospitable soils. As an example, after the Katmai eruption in 1912 and the Mount St. Helens eruption in 1980, Equisetum plants were the first to recolonize the heavy deposits of volcanic tephra.
Another means of reproduction used by Equisetum is sexual and is similar to the complicated reproduction of ferns. Some stems, called fertile stems, produce spores from a conelike structure, called a strobilus. The released spores have minute structures called elaters that change shape with varying humidity, and apparently help disperse them.
From a germinating spore comes the haploid gametophyte that has the ability to produce spermlike cells as well as egglike cells in a structure called an archegonium. The sperm require water to swim to the egg cell, and that explains why Equisetum is so often found in moist soils.
When these two cells combine, they form an embryo that develops into the sporophyte stage. We almost never get to see the gametophyte stage, since it is only 0.5 millimeters to 2 millimeters in length. However, we do see the sporophyte stems that erupt from any soil around the garden. The spore-forming strobilus sit on top of the sporophyte stage. There are also nonfertile sporophyte stems that photosynthesize sugars for growth of the deeply hidden rhizomes.
Equisetum is eaten by a number of Alaska’s big game animals. Surveys of black bear plant usage found that Equisetum is the 10th most important food source for them early in the spring. Brown bears are also known to eat this plant even though the nutritive value is relatively low. However, early in the spring when there isn’t much to eat, even low-nutrition food is better than nothing. Moose are also known to use Equisetum as a food source throughout the summer.
Humans have used Equisetum for hundreds of years for a variety of reasons. Some cultures consume the early shoots in a similar way to bears in the spring. It has also received various claims of its use for specific ailments. Some very early authors claim that a tea works as a diuretic, and the stems supposedly somehow function as a bleeding astringent.
More modern sources caution about these uses because the plant does contain the enzyme thiaminase that breaks down thiamin (B vitamins). In fact, a diet of more than 20 percent Equisetum will make horses very sick because of this enzyme. After ingesting too much Equisetum, horses can experience a variety of life-threatening cardiac and coordination problems.
The deep-living rhizomes of Equisetum have made it is almost impossible to remove them from our gardens. Some gardeners joke that the center of the Earth must be full of Equisetum rhizomes, and that is why they come back so quickly.
As I help the family gardener pull weeds around the house, I try to remember that these plants have earned their place in the garden by being here hundreds of millions of years before any humans walked the Earth. If their ability to populate so many different and harsh habitats is any indication, they will probably still be here long after we are gone.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.