Equisetum hyemale affine
Horsetail family (Equisetaceae)
Description: This native perennial plant is unbranched and 2-4' tall. It consists of a single central stem with multiple overlapping joints; the diameter of this stem spans up to ¾" across. The stems of Scouring Rush are green, olive-green, or dark green, rough in texture, and evergreen; they are usually erect. The joints that make up the central stem are individually several inches long; the upper joints are shorter than the lower joints. Each joint has about 10-40 fine ridges along its length. At the apex of each joint, there is an appressed ring-like sheath up to 1" long, from which the next joint develops. Except at its upper and lower rims, this sheath can be whitish grey, brown, or black; it is always black along the rim of its base, while its upper rim terminates in up to 40 tiny black teeth. These teeth are deciduous and often break off the stem. The interior cavity is quite large and spans at least one-half the diameter of a joint. Each fertile stem terminates in a spore-bearing cone up to 2" long on a short stalk. This cone is variably colored and usually pointed at the top. Infertile stems are very similar to fertile stems, except they lack spore-bearing cones. Secondary stems (branchlets) are rarely produced. The cones release their spores from late spring to mid-summer; they wither away later in the year. The root system consists of extensive rhizomes with fibrous secondary roots. This plant often forms dense colonies; sometimes these colonies can be quite large in size.
Cultivation: The preference is full sun, wet to moist conditions, and soil that is mucky, gravelly, or sandy. However, drier conditions and other kinds of soil are tolerated. This plant can spread aggressively, especially where the soil is poorly drained. It has few problems with pests and disease.
Range & Habitat: Scouring Rush is a common plant that occurs in every county of Illinois (see Distribution Map). Habitats include swales in black soil prairies and sand prairies, low-lying areas along rivers and ponds, marshes, roadside ditches, pastures, and gravelly railroad embankments (including the gravel ballast). This plant is found in both degraded and higher quality habitats; the typical variety of this species occurs in Eurasia.
Faunal Associations: Scouring Rush provides excellent cover for various kinds of wildlife, including wetland birds, small mammals, and insects. Because the tough stems have coarse fibers and silica deposits, they are not bothered by mammalian herbivores. The food value of this species to most kinds of wildlife is low.
Photographic Location: A low-lying area along a pond in Champaign, Illinois. The spore-bearing cone in the lower photograph is starting to wither away.
Comments: This is the largest Equisetum sp. (Horsetail) in Illinois; it is somewhat unusual in having evergreen stems. I am always impressed by the large dense colonies that are often formed by the stems of this plant. These tough stems were used to scour pots, pans, and floors during pioneer days, hence the common name. However, the Scouring Rush is not a rush, but a horsetail. The horsetails are closely related to ferns and both were common during the Carboniferous period (280-345 million years ago), when tree-sized horsetails and ferns occurred. The coal deposits of Illinois were formed in large part from the ancestral plants of today's horsetails and ferns. Scouring Rush can be distinguished from other horsetails in the state by its large size, rough unbranched stems, and pointed cones. While there is some variability across local populations, this species is usually easy to identify. However, sometimes it forms sterile hybrids with other horsetails. When this occurs, it is possible to confuse the hybrid with one of the parent species.