Horsetail family (Equisetaceae)
Description: This native perennial plant produces fertile and infertile shoots that are deciduous. Each fertile shoot is unbranched and about 4-6" tall. It has a central stalk that is light brown to brown and about ¼" across in diameter. This stalk terminates in a spore-bearing cone up to 1" long; the cone is oblongoid in shape and rounded at the top. The surface of the cone is mostly brown, but it is covered with spore-bearing tubercles that have black and white markings. The fertile shoots develop during mid-spring, but soon wither away after the cones have released their spores. The infertile (or vegetative) shoots have a very different appearance. They develop during late spring and persist until the fall. The infertile shoots are ½2' tall; they have whorls of branchlets along at least the upper half of their stems. The stems and branchlets of these shoots are slender and green. Each central stem consists of several joints; at the apex of each joint (except the uppermost), there is a short sheath with 3-4 teeth along its upper rim. This sheath is appressed to slightly spreading and green to brown. The base of the next joint develops from this sheath. Each joint is terete with 10-14 ridges along its length; sometimes there are more or fewer ridges. Initially, the branchlets are similar to the central stems, except they are much smaller in size. Later, they become almost as long as the stems. At this stage, the infertile shoots resemble small conifers because of the long needle-like branchlets. The branchlets have joints with sheaths like the stems, but there are only 3-4 teeth along the upper rim of each sheath. Usually, these branchlets are unbranched, but sometimes they produce secondary branchlets. An infertile shoot may produce a small infertile cone at its apex, but this is very unusual. Both the stems and branchlets of Common Horsetail are mostly solid. The root system consists of long rhizomes and secondary fibrous roots. This plant often forms colonies.
Cultivation: The preference is full or partial sun and moist to mesic conditions. Different kinds of soil are readily tolerated, including those containing sand, gravel, and fertile loam. This plant spreads readily by its rhizomes and can be very aggressive. It is possible to eliminate a vegetative colony by spreading a black plastic sheet across the entire area where it occurs. This sheet should remain in place for at least a year.
Range & Habitat: Common Horsetail is found in every county of Illinois and is quite common (see Distribution Map). Habitats include savannas, sandy savannas, black soil prairies, sand prairies, gravel prairies, dolomite prairies, thickets, fens, seeps, ditches, roadsides, areas along railroads (including the gravel ballast), old fields, and waste areas. This plant is often found in degraded areas and is rather weedy; however, it also occurs in higher quality habitats, especially where the soil is rather sandy or gravelly.
Faunal Associations: Where it occurs in dense colonies, Common Horsetail provides cover for small mammals and birds. The coarse stems are not often eaten by mammalian herbivores because of their silica deposits; these stems are also somewhat toxic because thiamin-deficiency can result if they are eaten by the same animals. Overall, the ecological value of this plant to wildlife is low.
Photographic Location: The photograph of the infertile shoot was taken near a railroad in Urbana, Illinois, while the photograph of the fertile shoot was taken at the webmaster's apartment complex in the same city.
Comments: This odd little plant is the most common and weedy horsetail in Illinois. The cone-bearing fertile shoots resemble brown mushrooms (something like the morel mushroom), while the infertile shoots look like small conifers during the summer. Few people realize that both types of shoots are produced from the rhizomes of the same plant. Common Horsetail differs from other horsetails by its brown fertile shoots, which lack chlorophyll. Other Equisetum spp. (Horsetails) in Illinois produce green fertile shoots that are similar to infertile shoots in appearance. The whorled branchlets of Common Horsetail can become almost as long as the central stem they are produced in great abundance and often obscure the central stem's visibility by the beginning of summer. Other Horsetails produce branchlets that are much shorter than their stems, or they produce no branchlets at all. There are other technical differences between Common Horsetail and other Horsetails, but it is usually easy to identify in the field.