A Horsetail is any plant of the genus Equisetum; the single surviving genus of a large group of primitive vascular plants. It is named the, "horsetail" because the stalk resembles a horse's tail. The name Equisetum comes from the Latin roots equus, meaning, "horse" and seta, meaning, "bristle." It doesn't make flowers but produces spores like the fern.
The horsetail grows to about 18 inches high. It is dark-green with a hollow, jointed or segmented stems usually 1/4 to 1/2 inches thick with no true leaves. Horsetails have whorls of small scale-like leaves around the stem that is green and it uses photosynthesis to gain energy. Stems may be singular or have whorls of branches. Only single stems produce the cone-shaped spore producing body at the tip. Horsetail stems contain silicon crystals embedded in its tissue. This gritty texture gives it the common name of "scouring rush".
Horsetails are a very common plant grown almost anywhere where water is plentiful, but can be found in rather hot climates such as Australia and cold climates such as the arctic. Horsetail is found throughout parts of Europe, Asia, the Middle East, and North America.
A long time ago, the Romans used it for cleaning equipment.