There are those who plead eloquently for the healing virtues of the "dull and flowerless weed" known as horsetail. Equisetum arvense L. (family Equisetaceae) is technically a pteridophyte and thus is more closely related to the ferns than to the flowering plants. Horsetail is a rushlike perennial with hollow, jointed stems and scalelike leaves, reproducing by means of spores, not seeds. The stems contain large amounts of silica and silicic acids (5 to 8 percent) that account for its use as a metal polisher and its synonym of souring rush. Several closely related species of Equisetum are similar to E. arvense in appearance and use. Another commonly used species is E. hymale L.