See text Equisetum (/ˌɛkwɪˈsiːtəm/; horsetail) is the only living genus in Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.

The pattern of spacing of nodes in horsetails, wherein those toward the apex of the shoot are increasingly close together, is said to have inspired John Napier to invent logarithms.

The latter name refers to the rush-like appearance of the plants and to the fact that the stems are coated with abrasive silicates, making them useful for scouring (cleaning) metal items such as cooking pots or drinking mugs, particularly those made of tin.

Equisetum hyemale, rough horsetail, is still boiled and then dried in Japan to be used for the final polishing process on woodcraft to produce a smooth finish.

However, it has recently been recognised that horsetail microphylls are probably not ancestral as in lycophytes (clubmosses and relatives), but rather derived adaptations, evolved by reduction of megaphylls.

In many species the cone-bearing shoots are unbranched, and in some (e.g. E. arvense, field horsetail) they are non-photosynthetic, produced early in spring.

[12] The crude cell extracts of all Equisetum species tested contain mixed-linkage glucan : xyloglucan endotransglucosylase (MXE) activity.

In addition, the cell walls of all Equisetum species tested contain mixed-linkage glucan (MLG), a polysaccharide which, until recently, was thought to be confined to the Poales.

The presence of MXE activity in Equisetum suggests that they have evolved MLG along with some mechanism of cell wall modification.

[20][21] Silicified remains of Equisetum thermale from the Late Jurassic of Argentina exhibit all the morphological characters of modern members of the genus.

[21] E. bogotense E. palustre E. pratense E. telmateia E. braunii E. sylvaticum E. diffusum E. fluviatile E. arvense E. scirpoides E. variegatum E. ramosissimum E. hyemale E. praealtum E. laevigatum E. myriochaetum E. giganteum E. bogotense E. pratense E. palustre E. sylvaticum E. × fontqueri E. telmateia E. arvense E. × litorale E. × dycei E. fluviatile E. scirpoides E. variegatum E. ramosissimum E. hyemale E. × trachyodon E. giganteum E. × schaffneri E. myriochaetum E. × ferrissii E. laevigatum The genus Equisetum as a whole, while concentrated in the non-tropical northern hemisphere, is near-cosmopolitan, being absent naturally only from Antarctica, Australia, New Zealand, and the islands of the Pacific Ocean.

[26][9] Northern North America (Canada and the northernmost United States), also has nine species (E. arvense, E. fluviatile, E. laevigatum, E. palustre, E. praealtum, E. pratense, E. scirpoides, E. sylvaticum, and E. variegatum).

The fertile stems bearing strobili of some species can be cooked and eaten like asparagus[34] (a dish called tsukushi (土筆) in Japan[35][failed verification]).

[39] If eaten over a long enough period of time, some species of horsetail can be poisonous to grazing animals, including horses.

[44] Analysis of the scratch marks on hadrosaur teeth is consistent with grazing on hard plants like horsetails.