Horsetail is a perennial, rush-like herb found in all parts of the world except New Zealand and Australia. Common along stream banks and in moist woods and meadows, the plant appears in two distinct phases, one fertile, the other sterile. In the fertile first stage, which occurs in early spring, the plant grows from 10 to 20 centimeters in height, with brownish, tubular stalks that resemble asparagus. Small flower spikes occur at the tops of the stalks. In the second, sterile stage, horsetail grows whorls of slender, jointed branches, up to a half meter in height. The stems from the second phase are used for health purposes.
Horsetail contains high concentrations of silica, along with a saponin known as equisetonin and several flavone glycosides.
The daily dosage for horsetail approved by Commission E is 6 grams of fresh or dried stems, or equivalent preparations. The herb has no known side effects at this dosage range.