The Equisetaceae are an ancient group of plants. Those with branched stems are kown as horsetails; those with unbranched stems are known as scouring rushes.
Sterile Stems: to 50 cm, mostly erect but sometimes partly decumbent, green; rough surface with 12 or more ridges
Nodes: ~ 5 cm apart; sheathes widening upward, about as long as wide, light brown at base, dark brown at top; teeth dark, narrow, often adhering to one another in pairs, deciduous
Branches: horizontal or up-swept, solid, rough; lowest branch usually as long or longer than upper branches; 3-4 sided; sheathes light brown at base, dark brown at top; 3-4 sharp-tipped black teeth; first internode of branch is always longer than the sheath of the node from which it arises.
Cavity: central cavity small, ~ 1/4 to 1/3 diameter of the stem; vallecular canals large
Fertile Stem: to 15 cm, erect, straw-colored, succulent, soon withers; may have stubby whorled branches; sheaths large with large dark teeth
Cone: 2-3 cm long, on long stem, blunt tipped
Habitat: grows in a wide variety of habitats from dry sand banks to moist semi-shaded woodlands
Similar Species: It is most likely to be confused with Equisetum pratense, Meadiw Horsetail. The characters overlap somewhat: (1) E. arvense usually has stouter and rougher branches, but when growing in the shade they may be somewhat thinner; (2) E. arvense usually has more upswept branches, but when growing in the shade they may be more horizontal; (3) the first internode of the lateral branches is usually longer in E. arvense than in E. pratense. Although at first it may seem difficult to differentiate between these species, if one uses all of the characters it is usually easy to determine the identity of a specimen.