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Title: Horsetails  
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Subject: Meristem, Foreland, Fossil Detectives
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"Horsetail" redirects here. For other uses, see Horse tail (disambiguation).
Temporal range: Callovian [1] to Recent
"Candocks" of the Great Horsetail (Equisetum telmateia telmateia), showing whorls of branches and the tiny dark-tipped leaves
Scientific classification
Kingdom: Plantae
Division: Pteridophyta
Class: Equisetopsida
Order: Equisetales
Family: Equisetaceae
Genus: Equisetum

see text

Equisetum (/ˌɛkwɨˈstəm/; horsetail, snake grass, puzzlegrass) is the only living genus in Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.[2]

Equisetum is a "living fossil" as it is the only living genus of the entire class Equisetopsida, which for over one hundred million years was much more diverse and dominated the understory of late Paleozoic forests. Some Equisetopsida were large trees reaching to 30 meters tall.[3] The genus Calamites of the family Calamitaceae, for example, is abundant in coal deposits from the Carboniferous period.

A superficially similar but entirely unrelated flowering plant genus, mare's tail (Hippuris), is occasionally misidentified as "horsetail".

It has been suggested that the pattern of spacing of nodes in horsetails, wherein those toward the apex of the shoot are increasingly close together, inspired John Napier to discover logarithms.[4]


The name "horsetail", often used for the entire group, arose because the branched species somewhat resemble a horse's tail. Similarly, the scientific name Equisetum derives from the Latin equus ("horse") + seta ("bristle").

Other names include candock for branching individuals, and snake grass or scouring-rush for unbranched or sparsely branched individuals. The latter name refers to the rush-like appearance 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. In German, the corresponding name is Zinnkraut ("tin-herb"). Rough horsetail E. hyemale is still boiled and then dried in Japan, to be used for the final polishing process on woodcraft to produce a smoother finish than any sandpaper.

Distribution, ecology and uses

The genus Equisetum is near-cosmopolitan, being absent only from Antarctica, though they are not known to be native to Australia, New Zealand nor the islands of the Pacific. They are perennial plants, either herbaceous and dying back in winter as most temperate species, or evergreen as most tropical species and the temperate species rough horsetail (E. hyemale), branched horsetail (E. ramosissimum), dwarf horsetail (E. scirpoides) and variegated horsetail (E. variegatum). They typically grow 0.2-1.5 m tall, though the "giant horsetails" are recorded to grow as high as 2.5 m (northern giant horsetail, E. telmateia), 5 m (southern giant horsetail, E. giganteum) or 8 m (Mexican giant horsetail, E. myriochaetum), and allegedly even more.[5]

Many species in this genus prefer wet sandy soils, though some are semi-aquatic and others are adapted to wet clay soils. The stalks arise from rhizomes that are deep underground and almost impossible to dig out. The field horsetail (E. arvense) can be a nuisance weed, readily regrowing from the rhizome after being pulled out. It is also unaffected by many herbicides designed to kill seed plants. However, as E. arvense prefers an acid soil, lime may be used to assist in eradication efforts to bring the soil pH to 7 or 8.[6] Members of the genus have been declared noxious weeds in Australia and in the US state of Oregon.[7][8]

All the Equisetum are classed as "unwanted organisms" in New Zealand and are listed on the National Pest Plant Accord.

If eaten over a long enough period of time, some species of horsetail can be poisonous to grazing animals, including horses.[9] The toxicity appears to be due to thiaminase enzymes, which can cause thiamine deficiency.[10][11][12][13] People have regularly consumed horsetails. The young plants are eaten cooked or raw, but considerable care must be taken.[14] For example, the fertile stems bearing strobili of some species are cooked and eaten like asparagus (a dish called tsukushi[15]) in Japan.[16] The people of ancient Rome would eat meadow horsetail in a similar manner, but they also used it to make tea as well as a thickening powder.[17] Indians of the North American Pacific Northwest eat the young shoots of this plant raw.[18] The plants are used as a dye and give a soft green colour. An extract is often used to provide silica for supplementation. Horsetail was often used by Indians to polish wooden tools. Equisetum species are often used to analyze gold concentrations in an area due to their ability to take up the metal when it is in a solution.[17]


In these plants the leaves are greatly reduced and usually non-photosynthetic. They contain a single, non-branching vascular trace, which is the defining feature of microphylls. However, it has recently been recognised that horsetail microphylls are probably not ancestral as in Lycopodiophyta (clubmosses and relatives), but rather derived adaptations, evolved by reduction of megaphylls.[19] They are, therefore, sometimes actually referred to as megaphylls to reflect this homology.

The leaves of horsetails are arranged in whorls fused into nodal sheaths. The stems are green and photosynthetic, and are distinctive in being hollow, jointed and ridged (with sometimes 3 but usually 6-40 ridges). There may or may not be whorls of branches at the nodes.


The spores are borne under sporangiophores in strobili, cone-like structures at the tips of some of the stems. In many species the cone-bearing shoots are unbranched, and in some (e.g. field horsetail, E. arvense) they are non-photosynthetic, produced early in spring separately from photosynthetic, sterile shoots. In some other species (e.g. marsh horsetail, E. palustre) they are very similar to sterile shoots, photosynthetic and with whorls of branches.

Horsetails are mostly homosporous, though in the field horsetail smaller spores give rise to male prothalli. The spores have four elaters that act as moisture-sensitive springs, assisting spore dispersal after the sporangia have split open longitudinally.



The living members of the genus Equisetum are divided into two distinct lineages, which are usually treated as subgenera. Hybrids are common, but hybridization has only been recorded between members of the same subgenus.[20]

In addition, there are numerous ill-determined populations. One of them, the Kamchatka Horsetail (Equisetum camtschatcense),[verification needed] is an ornamental forming imposing stands of these archaic plants.

Subgenus Equisetum
  • Template:Tx – Field Horsetail, Common Horsetail or Giant Horsetail
  • Template:Tx – Andean Horsetail or Giant Horsetail
  • Template:Tx – Himalayan Horsetail
  • Template:Tx – Water Horsetail
  • Template:Tx – Marsh Horsetail
  • Template:Tx – Meadow Horsetail, Shade Horsetail, Shady Horsetail
  • Template:Tx – Wood Horsetail
  • Template:Tx – Great Horsetail, Northern Giant Horsetail
Subgenus Hippochaete
  • Template:Tx – Southern Giant Horsetail or Giant Horsetail
  • Template:Tx – Mexican Giant Horsetail or Giant Horsetail
  • Template:Tx – Rough Horsetail, Scouringrush Horsetail
  • Template:Tx – Smooth Horsetail
  • Template:Tx – Branched Horsetail
  • Template:Tx – Dwarf Horsetail
  • Template:Tx – Variegated Horsetail
unplaced to subgenus

Named hybrids

Hybrids between species in subgenus Equisetum
  • Template:Tx (Equisetum sylvaticum × Equisetum telmateia)
  • Template:Tx (Equisetum fluviatile × Equisetum palustre)
  • Template:Tx (Equisetum palustre × Equisetum telmateia)
  • Template:Tx (Equisetum arvense × Equisetum fluviatile)
  • Template:Tx (Equisetum fluviatile × Equisetum pratense)
  • Template:Tx (Equisetum pratense × Equisetum sylvaticum)
  • Template:Tx (Equisetum arvense × Equisetum telmateia)
  • Template:Tx (Equisetum arvense × Equisetum palustre)
  • Template:Tx (Equisetum fluviatile × Equisetum telmateia)
Hybrids between species in subgenus Hippochaete
  • Template:Tx (Equisetum hyemale × Equisetum laevigatum)
  • Template:Tx (Equisetum hyemale × Equisetum ramosissimum)
  • Template:Tx (Equisetum laevigatum × Equisetum variegatum)
  • Template:Tx (Equisetum giganteum × Equisetum myriochaetum)
  • Template:Tx (Equisetum hyemale × Equisetum variegatum)

Equisetum cell walls

The crude cell extracts of all Equisetum species tested contain mixed-linkage glucan : Xyloglucan endotransglucosylase (MXE) activity.[21] This is a novel enzyme and is not known to occur in any other plants. 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.[22][23] The evolutionary distance between Equisetum and the Poales suggests that each evolved MLG independently. The presence of MXE activity in Equisetum suggests that they have evolved MLG along with some mechanism of cell wall modification. The lack of MXE in the Poales suggests that there it must play some other, currently unknown, role. Due to the correlation between MXE activity and cell age, MXE has been proposed to promote the cessation of cell expansion.

Medicinal uses

The plant has a long history of medicinal uses, although modern sources include cautions with regard to its use.[14] In 2009 the European Food Safety Authority issued a report assessing health claims (invigoration, weight control, and skin, hair, and bone health) for Equisetum arvense L., concluding that none could be substantiated.[24]

See also


Further reading

  • Walkowiak, Radoslaw (2008): IEA – Taxonomy. Version of 2008-10-04. Retrieved 2011-11-07.
  • Pryer, K.M.; Schuettpelz, E.; Wolf, P.G.; Schneider, H.; Smith, A.R. & Cranfill, R. (2004): Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences. PDF fulltext
  • expand by hand
  • Weber, Reinhard (2005): Equisetites aequecaliginosus sp. nov., ein Riesenschachtelhalm aus der spättriassischen Formation Santa Clara, Sonora, Mexiko [Equisetites aequecaliginosus sp. nov., a tall horsetail from the Late Triassic Santa Clara Formation, Sonora, Mexico]. Revue de Paléobiologie 24(1): 331-364 [German with English abstract]. PDf fulltext

External links

  • at the Tree of Life Web Project
  • The Wonderful World of Equisetum
  • International Equisetological Association
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