| Equisetum arvense|
Horsetails and scouring-rushes are plants of the genus Equisetum, the only genus in the family Equisetaceae, in the order Equisetales, in the class Sphenopsida, sometimes placed in its own division, Sphenophyta, or in the division Tracheophyta or Archeophyta. They are considered fern allies.
These are plants without leaves, but with hollow, jointed, ascending stems that may or may not have side-branches radiating out from the nodes, depending on species.
Usually, the name horsetail is applied to the branching species, while the name scouring-rush is applied to the unbranched species. The name horsetail arose because it was thought that the stalk resembled a horse's tail; the name Equisetum means "horse hair". The name scouring-rush refers both to its rush-like appearance and to the fact that the stems accumulate silica and have been used for scouring dishes.
The spore is borne in cone-like structures at the tips of the stalks.
Most plants in this genus prefer sandy soils.
Horsetails are considered a difficult weed by many British gardeners, because they tend to reappear after being pulled out of a garden.