Horsetail , the name of plants of the genus equisetum (Lat. equus, a horse, and seta, a bristle), which belongs to the great series of cryptogamous or flowerless plants. They have rush-like, hollow, jointed stems, with toothed sheaths at the joints, and terminated by a sort of cone of shield-shaped scales; the spore cases or parts concerned in reproduction are attached to the under side of these scales; each spore has attached to it four long elastic filaments, which coil closely around it when moist, and uncoil when dry; these motions, which may be induced at will by breathing upon the spores, render them interesting ob-. jects for the microscope. The cuticle of these plants abounds so largely in silex that some are used in polishing; hence scouring rush is the common name for some species. The most common or field horsetail, E. arvense, is a plant of wide distribution, it being found in every continent and from the Arctic zone to Africa; this species is of interest chiefly as it is alleged to be poisonous to cattle. Like some others, it produces two sorts of stems; the fertile ones, which appear in very early spring, especially in moist places, are 4 to 10 in. high, simple, succulent, of a light brown color with black sheaths, and wither soon after the spores are discharged.
The barren stems appear later, and are green and ribbed, appearing quite unlike the others; they bear numerous generally simple branches at each node, and have so much the appearance of a young seedling pine-tree that in some localities the plant is called low pine and ground pine. The plant is very generally regarded by farmers as poisonous to animals, but in this, as in other cases of plants reputed to be injurious, it is very difficult to procure positive evidence. It would seem to be quite certain that the dried plant is not poisonous, as it is often cut with the grass when mown for hay, and we have known hay largely mixed with horsetail to be fed without injury. The sterile stem of this is also annual. There are several perennial-stemmed species, the largest of which, E. robustum, 3 to 6 ft. high, grows along the western rivers.
Common Horsetail (Equisetum arvense) - Scales and Spores, and Barren and Fertile Stems.