Editing Equisetum

{{Short description|Genus of vascular plants}}
{{Redirect|Horsetail|other uses|Horse tail (disambiguation)}}
{{Automatic taxobox
| fossil_range = {{fossilrange|Pliensbachian|Present|Early Jurassic–present}}
| image = Equisetum telmateia, Ireland 1 - Ragnhild & Neil Crawford.jpg
| image_caption = Vegetative stems of ''[[Equisetum telmateia]]'' (great horsetail), showing whorls of branches and the tiny dark-tipped leaves
| taxon = Equisetum
| authority = [[Carl Linnaeus|L.]]
| type_species = ''[[Equisetum arvense]]''
| type_species_authority = [[Carl Linnaeus|L.]]
| subdivision_ranks = [[Species]]
| subdivision = See text
| synonyms = 
*''Allostelites'' <small>Börner</small>
*''Hippochaete'' <small>Milde</small>
| synonyms_ref = <ref name=powo>{{cite web |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30002112-2 |title=''Equisetum'' L. |author=<!--Not stated--> |date=2024 |website=Plants of the World Online |publisher=Board of Trustees of the Royal Botanic Gardens, Kew |access-date=15 September 2024 }}</ref>
}}

'''''Equisetum''''' ({{IPAc-en|ˌ|ɛ|k|w|ᵻ|ˈ|s|iː|t|əm}}; '''horsetail''') is the only living [[genus]] in [[Equisetaceae]], a [[family (biology)|family]] of [[vascular plant]]s that reproduce by [[spore]]s rather than seeds.<ref>{{cite book |last1=Dunmire |first1=John R. |last2=Williamson |first2=Joseph F. |editor1-last=Brenzel |editor1-first=Kathleen N. |title=Western Garden Book |date=1995 |publisher=Sunset |location=Menlo Park, CA |isbn=0376038500 |pages=274, 606 |url=https://archive.org/details/sunsetwesterngar00suns |chapter=EQUISETUM hyemale |url-access=registration}}</ref>

''Equisetum'' is a "[[living fossil]]", the only living genus of the entire [[class (biology)|subclass]] [[Equisetidae]], which for over 100 million years was much more diverse and dominated the [[understorey]] of late [[Paleozoic]] forests. Some equisetids were large [[tree]]s reaching to {{cvt|30|m|ft|0}} tall.<ref>{{cite web |url=http://www.fiu.edu/~chusb001/GiantEquisetum/Intro_Equisetum.html |publisher=[[Florida International University]] |title=An Introduction to the Genus ''Equisetum'' and the Class Sphenopsida as a whole |access-date=2009-07-22 |url-status=dead |archive-url=https://web.archive.org/web/20090714050011/http://www.fiu.edu/~chusb001/GiantEquisetum/Intro_Equisetum.html |archive-date=2009-07-14 }}</ref> The genus ''[[Calamites]]'' of the family [[Calamitaceae]], for example, is abundant in [[coal]] deposits from the [[Carboniferous]] period. 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 [[logarithm]]s.<ref>{{cite magazine |last1=Sacks |first1=Oliver |date=25 July 2011 |title=Hunting Horsetails |url=https://www.newyorker.com/magazine/2011/08/01/hunting-horsetails |department=The Talk of the Town: Field Trip |magazine=[[The New Yorker]] |issue=11 August 2011}}</ref> Modern horsetails first appeared during the [[Jurassic]] period.

A superficially similar but entirely unrelated [[flowering plant]] genus, mare's tail (''[[Hippuris]]''), is occasionally referred to as "horsetail", and adding to confusion, the name "mare's tail" is sometimes applied to ''Equisetum''.<ref>{{cite OED|Equisetum}}</ref>

==Etymology==
{{More citations needed|section|date=August 2018}}
The name "horsetail", often used for the entire group, arose because the branched species somewhat resemble a [[horse]]'s tail. Similarly, the [[Binomial nomenclature|scientific name]] ''Equisetum'' is derived from the [[Latin]] {{lang|la|equus}} ('horse') + {{lang|la|seta}} ('bristle').<ref>{{cite book |page= 283 |title= Florida Ethnobotany |author= Daniel F. Austin |edition=illustrated |publisher= CRC Press |year= 2004 |isbn= 9780203491881}}</ref>

Other names include '''candock''' for branching species, '''marestail''', '''puzzlegrass''', and '''snake grass''' or '''scouring-rush''' for unbranched or sparsely branched species. The latter name refers to the [[Juncus|rush]]-like appearance of the plants and to the fact that the stems are coated with abrasive [[silicate]]s, 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 [[Woodworking|woodcraft]] to produce a smooth finish.<ref name=Husby>{{cite journal |first=C |last=Husby |date=2013 |title=Biology and functional ecology of ''Equisetum'' with emphasis on the giant horsetails |journal=Botanical Review |volume=79 |issue=2 |pages=147–177 |doi=10.1007/s12229-012-9113-4 |bibcode=2013BotRv..79..147H |s2cid=15414705 }}</ref> In [[German language|German]], the corresponding name is {{lang|de|Zinnkraut}} ('tin-herb'). In [[Spanish language|Spanish]]-speaking countries, these plants are known as {{lang|es|cola de caballo}} ('horsetail').

==Description==
[[File:Equisetum arvense 001.JPG|right|thumb|''[[Equisetum arvense]]'' (field horsetail)]]
''Equisetum'' [[Leaf|leaves]] are greatly reduced and usually non-[[Photosynthesis|photosynthetic]]. They contain a single, non-branching [[vascular bundle|vascular trace]], which is the defining feature of [[microphyll]]s. However, it has recently been recognised that horsetail microphylls are probably not ancestral as in [[lycophyte]]s (clubmosses and relatives), but rather derived [[adaptation]]s, evolved by reduction of [[wikt:megaphyll|megaphylls]].<ref>{{cite journal |last=Rutishauser |first=R |s2cid=4658142 |title=Polymerous leaf whorls in vascular plants: Developmental morphology and fuzziness of organ identities |journal=International Journal of Plant Sciences |volume=160 |issue=S6 |pages=S81–S103 |date=November 1999 |pmid=10572024 |doi=10.1086/314221|bibcode=1999IJPlS.160S..81R }}</ref>

The leaves of horsetails are arranged in [[Whorl (botany)|whorls]] fused into [[node (botany)|nodal]] sheaths. The stems are usually green and photosynthetic, and are distinctive in being hollow, jointed and ridged (with sometimes 3 but usually 6–40&nbsp;ridges). There may or may not be whorls of branches at the nodes.<ref name = Streeter>Streeter D, Hart-Davies C, Hardcastle A, Cole F, Harper L. 2009. ''Collins Flower Guide''. Harper Collins {{ISBN|9-78-000718389-0}}</ref> Unusually, the branches often emerge below the leaves in an internode, and grow from buds between their bases.

[[Image:Horsetail vegeative stem.JPG|120px|thumb|Vegetative stem:<br/>B = branch in whorl<br/>I = internode<br/>L = leaves<br/>N = node]]
[[Image:Equisetum braunii (strobilus), Portland, Oregon.jpg|thumb|Strobilus of ''[[Equisetum braunii]]'', terminal on an unbranched stem]]
[[Image:Microscopic view of Equisetum in Japan one 20thmm graduation.jpg|thumb|Microscopic view of ''[[Equisetum hyemale]]'' (rough horsetail) (2-1-0-1-2 is one [[millimetre]] with {{frac|1|20}}th [[graduation (scale)|graduation]]).<br/>The small white protuberances are accumulated [[silicate]]s on [[Cell (biology)|cell]]s.]]

===Spores===
The [[spore]]s are borne under [[sporangiophore]]s in [[strobilus|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. ''[[Equisetum arvense|E.&nbsp;arvense]]'', field horsetail) they are non-photosynthetic, produced early in spring. In some other species (e.g. ''[[Equisetum palustre|E.&nbsp;palustre]]'', marsh horsetail) they are very similar to sterile shoots, photosynthetic and with whorls of branches.<ref name=Stace>{{cite book|last=Stace|first=C. A.|author-link = Stace, C. A.|year=2019|title=New Flora of the British Isles|edition=Fourth|publisher=C & M Floristics|location = Middlewood Green, Suffolk, U.K.| isbn=978-1-5272-2630-2}}</ref>{{rp|12–15}}

Horsetails are mostly [[Spore|homosporous]], though in the field horsetail, smaller spores give rise to male [[Prothallus|prothalli]]. The spores have four [[elater]]s that act as moisture-sensitive springs, assisting spore dispersal through crawling and hopping motions after the [[Sporangium|sporangia]] have split open longitudinally.<ref>{{cite news |last1=Gill |first1=Victoria |title=Horsetail plant spores use 'legs' to walk and jump |url=https://www.bbc.com/news/science-environment-24025365 |work=[[BBC News]] |date=11 September 2013}}</ref> They are photosynthetic and have a lifespan that is usually two weeks at most, but will germinate immediately under humid conditions and develop into a [[gametophyte]].<ref>{{cite journal | pmc=4469821 | date=2015 | last1=Zhao | first1=Q. | last2=Gao | first2=J. | last3=Suo | first3=J. | last4=Chen | first4=S. | last5=Wang | first5=T. | last6=Dai | first6=S. | title=Cytological and proteomic analyses of horsetail (Equisetum arvense L.) spore germination | journal=Frontiers in Plant Science | volume=6 | page=441 | doi=10.3389/fpls.2015.00441 | doi-access=free | pmid=26136760 | bibcode=2015FrPS....6..441Z }}</ref>

===Cell walls ===
The crude cell extracts of all ''Equisetum'' species tested contain [[mixed-linkage glucan : xyloglucan endotransglucosylase]] (MXE) activity.<ref>{{Cite journal | last1 = Fry | first1 = S. C. | last2 = Mohler | first2 = K. E. | last3 = Nesselrode | first3 = B. H. W. A. | last4 = Frankov | first4 = L. | title = Mixed-linkage -glucan:xyloglucan endotransglucosylase, a novel wall-remodelling enzyme from ''Equisetum'' (horsetails) and charophytic algae | doi = 10.1111/j.1365-313X.2008.03504.x | journal = The Plant Journal | volume = 55 | issue = 2 | pages = 240–252 | year = 2008 | pmid = 18397375| doi-access = free }}</ref> 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]].<ref>{{cite journal|pmid=18393951 | doi=10.1111/j.1469-8137.2008.02435.x|title=Mixed-linkage (1→3,1→4)-β-d-glucan is a major hemicellulose of ''Equisetum'' (horsetail) cell walls|year=2008|last1=Fry|first1=Stephen C.|last2=Nesselrode|first2=Bertram H. W. A.|last3=Miller|first3=Janice G.|last4=Mewburn|first4=Ben R.|journal=New Phytologist|volume=179|pages=104–15|issue=1|doi-access=free| bibcode=2008NewPh.179..104F}}</ref><ref>{{cite journal|pmid=18284587 | doi=10.1111/j.1365-313X.2008.03453.x|title=Mixed-linkage (1→3),(1→4)-β-d-glucan is not unique to the Poales and is an abundant component of ''Equisetum arvense'' cell walls|year=2008|last1=Sørensen|first1=Iben|last2=Pettolino|first2=Filomena A.|last3=Wilson|first3=Sarah M.|last4=Doblin|first4=Monika S.|last5=Johansen|first5=Bo|last6=Bacic|first6=Antony|last7=Willats|first7=William G. T.|journal=The Plant Journal|volume=54|issue=3|pages=510–21|doi-access=free}}</ref> 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. Non-''Equisetum'' land plants tested lack detectable MXE activity. An observed negative correlation between [[Xyloglucan endotransglucosylase|XET]] activity and cell age led to the suggestion that XET is catalysing endotransglycosylation in controlled wall-loosening during cell expansion.<ref>{{cite journal|last1=Simmons|first1=Thomas J.|last2=Fry|first2=Stephen C. |url=http://www.biochemj.org/content/474/7/1055|title=Bonds broken & formed during the mixed-linkage glucan: xyloglucan endotransglucosylase reaction catalysed by Equisetum hetero-trans-β-glucanase|date=2017|journal= Biochemical Journal|doi=10.1042/BCJ20160935|pmc=5341106|pmid=28108640|volume=474|issue=7|pages=1055–1070|access-date=2019-07-17}}</ref> 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.{{citation needed|date=August 2016}}

==Taxonomy==
===Species===
Currently, 18 species of ''Equisetum'' are accepted by [[Plants of the World Online]].<ref name=powo/> The living members are divided into three distinct lineages, which are usually treated as [[Subgenus|subgenera]]. The name of the type subgenus, ''Equisetum'', means "horse hair" in [[Latin]], while the name of the other large subgenus, ''Hippochaete'', means "horse hair" in [[Ancient Greek|Greek]]. [[Hybrid (biology)|Hybrid]]s are common, but hybridization has only been recorded between members of the same subgenus.<ref>{{Cite web
|url=http://www.btinternet.com/~pigott/equisetum/taxonsum.html|title=Summary of ''Equisetum'' Taxonomy|last=Pigott|first=Anthony|date=4 October 2001|website=National Collection of Equisetum|archive-url=https://web.archive.org/web/20121021201939/http://www.btinternet.com/~pigott/equisetum/taxonsum.html|archive-date=21 October 2012|url-status=dead|access-date=17 June 2013}}</ref>

Two ''Equisetum'' plants are sold under the names ''Equisetum japonicum'' (barred horsetail) and ''Equisetum camtschatcense'' (Kamchatka horsetail). These are both types of ''E.&nbsp;hyemale'' var. ''hyemale'', although they may also be listed as separate varieties of ''E.&nbsp;hyemale''.<ref>{{cite book |last1=Trounce |first1=Bob |last2=Hanson |first2=Cindy |last3=Lloyd |first3=Sandy |last4=Iaconis |first4=Linda |last5=Thorp |first5=John |title=Horsetails - ''Equisetum'' species |url=https://profiles.ala.org.au/opus/weeds-australia/profile/Equisetum%20spp. |website=WeedsAustralia |publisher=[[Atlas of Living Australia]], Centre for Invasive Species Solutions |format=PDF |date=2003 |isbn=1-920932-24-0 |access-date=2021-08-26 |archive-date=2021-08-26 |archive-url=https://web.archive.org/web/20210826185746/https://profiles.ala.org.au/opus/weeds-australia/profile/Equisetum%20spp. |url-status=dead }}</ref>{{Citation needed|date=October 2016}}

[[Image:Equisetum hyemale 02 by Line1.jpg|thumb|right|''[[Equisetum hyemale]]'' (rough horsetail) in [[Parc floral de Paris]]]]

=== Evolutionary history ===
The oldest remains of modern horsetails of the genus ''Equisetum'' first appear in the Early Jurassic, represented by ''[[Equisetum dimorphum]]'' from the Early Jurassic of Patagonia<ref>{{Cite journal|last1=Elgorriaga|first1=Andrés|last2=Escapa|first2=Ignacio H.|last3=Bomfleur|first3=Benjamin|last4=Cúneo|first4=Rubén|last5=Ottone|first5=Eduardo G.|date=February 2015|title=Reconstruction and Phylogenetic Significance of a New Equisetum Linnaeus Species from the Lower Jurassic of Cerro Bayo (Chubut Province, Argentina)|url=http://www.bioone.org/doi/10.5710/AMGH.15.09.2014.2758|journal=Ameghiniana|language=en|volume=52|issue=1|pages=135–152|doi=10.5710/AMGH.15.09.2014.2758|bibcode=2015Amegh..52..135E |issn=0002-7014|s2cid=6134534|hdl=11336/66623|hdl-access=free}}</ref> and ''[[Equisetum laterale]]'' from the Early-Middle Jurassic of Australia.<ref>Gould, R. E. 1968. Morphology of ''Equisetum laterale'' Phillips, 1829, and ''E. bryanii'' sp. nov. from the Mesozoic of south‐eastern Queensland. Australian Journal of Botany 16: 153–176.</ref><ref name="Elgorriaga-2018">{{Cite journal|last1=Elgorriaga|first1=Andrés|last2=Escapa|first2=Ignacio H.|last3=Rothwell|first3=Gar W.|last4=Tomescu|first4=Alexandru M. F.|last5=Rubén Cúneo|first5=N.|date=August 2018|title=Origin of Equisetum : Evolution of horsetails (Equisetales) within the major euphyllophyte clade Sphenopsida|journal=American Journal of Botany|language=en|volume=105|issue=8|pages=1286–1303|doi=10.1002/ajb2.1125|pmid=30025163|doi-access=free}}</ref> [[Petrifaction|Silicified]] remains of ''[[Equisetum thermale]]'' from the Late Jurassic of Argentina exhibit all the morphological characters of modern members of the genus.<ref>{{Cite journal|last1=Channing|first1=Alan|last2=Zamuner|first2=Alba|last3=Edwards|first3=Dianne|last4=Guido|first4=Diego|date=2011|title=Equisetum thermale sp. nov. (Equisetales) from the Jurassic San Agustín hot spring deposit, Patagonia: Anatomy, paleoecology, and inferred paleoecophysiology|journal=American Journal of Botany|language=en|volume=98|issue=4|pages=680–697|doi=10.3732/ajb.1000211|issn=1537-2197|pmid=21613167|doi-access=free|bibcode=2011AmJB...98..680C |hdl=11336/95234|hdl-access=free}}</ref> The estimated split between ''[[Equisetum bogotense]]'' and all other living ''Equisetum'' is estimated to have occurred no later than the Early Jurassic.<ref name="Elgorriaga-2018" />

====Subgenus ''Paramochaete''====
* {{txil|Equisetum bogotense|[[Carl Sigismund Kunth|Kunth]]}} – Andean horsetail; upland [[South America]] up to [[Costa Rica]]; includes ''E.&nbsp;rinihuense'', sometimes treated as a separate species. Previously included in subg. ''Equisetum'', but Christenhusz ''et al.'' (2019)<ref name="Christenhusz2019" /> transfer this here, as ''E.&nbsp;bogotense'' appears to be sister to all the remaining species in the genus.

====Subgenus ''Equisetum''====
* {{txil|Equisetum arvense|[[Carl Linnaeus|L.]]}} – field horsetail or common horsetail; circumboreal down through temperate zones
* {{txil|Equisetum braunii|[[Carl August Julius Milde|Milde]]}} – northern giant horsetail, syn. ''E. telmateia'' subsp. ''braunii'' (Milde) Hauke.; west coast of North America
* {{txil|Equisetum diffusum|[[David Don|D.Don]]}} – Himalayan horsetail; Himalayan India and China and adjacent nations above about {{convert|450|m}}
* {{txil|Equisetum fluviatile|L.}} – water horsetail; circumboreal down through temperate zones
* {{txil|Equisetum palustre|L.}} – marsh horsetail; circumboreal down through temperate zones
* {{txil|Equisetum pratense|[[Jakob Friedrich Ehrhart|Ehrh.]]}} – shady horsetail, meadow horsetail, shade horsetail; circumboreal except for tundra down through cool temperate zones
* {{txil|Equisetum sylvaticum|L.}} – wood horsetail; circumboreal down through cool temperate zones, more restricted in east Asia
* {{txil|Equisetum telmateia|Ehrh.}} – great horsetail; Europe to Asia Minor and north Africa. The former North American subspecies ''Equisetum telmateia'' subsp. ''braunii'' (Milde) Hauke is now treated as a separate species {{tx|Equisetum braunii|Milde}}<ref name="Christenhusz2019" /><ref name=powo/>
[[Image:Equisetum ramosissimum, Slavičín, Czech Republic.jpg|thumb|right|''[[Equisetum ramosissimum]]'' in the Czech Republic]]

====Subgenus ''Hippochaete''====
* {{txil|Equisetum giganteum|L.}} – southern giant horsetail or giant horsetail; temperate to tropical South America and Central America north to southern Mexico
* {{txil|Equisetum hyemale|L.}} – rough horsetail; most of non-tropical Old World. The former North American subspecies ''Equisetum hyemale'' subsp. ''affine'' <small>(Engelm.) A.A.Eat.</small> is now treated as a separate species {{tx|Equisetum praealtum|Raf.}}<ref name="Christenhusz2019" /><ref name=powo/>
* {{txil|Equisetum laevigatum|A.Braun}} – smooth horsetail, smooth scouringrush; western 3/4 of North America down into northwestern Mexico; also sometimes known as ''Equisetum kansanum''
* {{txil|Equisetum myriochaetum|[[Diederich Franz Leonhard von Schlechtendal|Schltdl.]] & [[Adelbert von Chamisso|Cham.]]}} – Mexican giant horsetail; from central Mexico south to Peru
* {{txil|Equisetum praealtum|[[Constantine Samuel Rafinesque|Raf.]]}} – scouringrush horsetail, syn. ''E. hyemale'' subsp. ''affine'' <small>(Engelm.) A.A.Eat.</small>; temperate North America
* {{txil|Equisetum ramosissimum|[[René Louiche Desfontaines|Desf.]]}} (including ''[[Equisetum debile|E.&nbsp;debile]]'') – branched horsetail; Asia, Europe, Africa, southwest Pacific islands
* {{txil|Equisetum scirpoides|[[André Michaux|Michx.]]}} – dwarf horsetail, dwarf scouringrush; northern (cool temperate) zones worldwide
* {{txil|Equisetum variegatum|[[Schleich.]] ex [[George Heinrich Weber|Weber]] & [[Charles Mohr (botanist)|Mohr]]}} – variegated horsetail, variegated scouringrush; northern (cool temperate) zones worldwide, except for northeasternmost Asia
* {{txil|Equisetum xylochaetum|[[Georg Heinrich Mettenius|Mett.]]}} – Atacama Desert giant horsetail; southern Peru, northern Chile

====Unplaced to subgenus====
*{{extinct}}''[[Equisetum dimorphum]]'' – [[Early Jurassic]], Argentina
*{{extinct}}''[[Equisetum laterale]] –'' Early to [[Middle Jurassic]], Australia
*{{extinct}}''[[Equisetum thermale]]'' – Middle to [[Late Jurassic]], Argentina
*{{extinct}}''[[Equisetum similkamense]]'' – [[Ypresian]], British Columbia

===Named hybrids===
[[Image:Equisetum x moorei3.JPG|thumb|right|[[Equisetum × moorei|''Equisetum'' × ''moorei'']] (''[[Equisetum hyemale|E.&nbsp;hyemale]]'' × ''[[Equisetum ramosissimum|E.&nbsp;ramosissiumum]]'')]]

====Hybrids between species in subgenus ''Equisetum''====
* [[Equisetum × bowmanii|''Equisetum'' × ''bowmanii'']] {{small|[[Christopher Nigel Page|C.N.Page]]}} (''Equisetum sylvaticum'' × ''Equisetum telmateia'')
* [[Equisetum × dycei|''Equisetum'' × ''dycei'']] {{small|C.N.Page}} (''Equisetum fluviatile'' × ''Equisetum palustre'')
* [[Equisetum × font-queri|''Equisetum'' × ''font-queri'']] {{small|[[Werner Rothmaler|Rothm.]]}} (''Equisetum palustre'' × ''Equisetum telmateia'')
* [[Equisetum × litorale|''Equisetum'' × ''litorale'']] {{small|Kühlew ex [[Franz Josef Ruprecht|Rupr.]]}} (''Equisetum arvense'' × ''Equisetum fluviatile'')
* [[Equisetum × mchaffieae|''Equisetum'' × ''mchaffieae'']] {{small|C.N.Page}} (''Equisetum fluviatile'' × ''Equisetum pratense'')
* [[Equisetum × mildeanum|''Equisetum'' × ''mildeanum'']] {{small|Rothm.}} (''Equisetum pratense'' × ''Equisetum sylvaticum'')
* [[Equisetum × robertsii|''Equisetum'' × ''robertsii'']] {{small|Dines}} (''Equisetum arvense'' × ''Equisetum telmateia'')
* [[Equisetum × rothmaleri|''Equisetum'' × ''rothmaleri'']] {{small|C.N.Page}} (''Equisetum arvense'' × ''Equisetum palustre'')
* [[Equisetum × willmotii|''Equisetum'' × ''willmotii'']] {{small|C.N.Page}} (''Equisetum fluviatile'' × ''Equisetum telmateia'')

====Hybrids between species in subgenus ''Hippochaete''====
* [[Equisetum × ferrissii|''Equisetum'' × ''ferrissii'']] {{small|[[Willard Nelson Clute|Clute]]}} (''Equisetum hyemale'' × ''Equisetum laevigatum'')
* [[Equisetum × moorei|''Equisetum'' × ''moorei'']] {{small|[[Edward Newman (entomologist)|Newman]]}} (''Equisetum hyemale'' × ''Equisetum ramosissimum'')
* [[Equisetum × nelsonii|''Equisetum'' × ''nelsonii'']] {{small|([[Alvah Augustus Eaton|A.A.Eaton]]) Schaffn.}} (''Equisetum laevigatum'' × ''Equisetum variegatum'')
* [[Equisetum × schaffneri|''Equisetum'' × ''schaffneri'']] {{small|Milde}} (''Equisetum giganteum'' × ''Equisetum myriochaetum'')
* [[Equisetum × trachyodon|''Equisetum'' × ''trachyodon'']] {{small|(A.Braun) W.D.J.Koch}} (''Equisetum hyemale'' × ''Equisetum variegatum'')

===Phylogeny===
{| class="wikitable"
|-
! colspan=1 |Christenhusz ''et al.'' 2019<ref name="Christenhusz2019">{{cite journal |last1=Christenhusz |first1=Maarten J M |last2=Bangiolo |first2=Lois |last3=Chase |first3=Mark W |last4=Fay |first4=Michael F |last5=Husby |first5=Chad |last6=Witkus |first6=Marika |last7=Viruel |first7=Juan |title=Phylogenetics, classification and typification of extant horsetails (''Equisetum'', Equisetaceae) |journal=Botanical Journal of the Linnean Society |date=April 2019 |volume=189 |issue=4 |pages=311–352 |doi=10.1093/botlinnean/boz002}}</ref> 
! colspan=1 |Nitta et al. 2022<ref>{{cite journal |last1=Nitta |first1=Joel H. |last2=Schuettpelz |first2=Eric |last3=Ramírez-Barahona |first3=Santiago |last4=Iwasaki |first4=Wataru |display-authors=et al. |year=2022 |title=An Open and Continuously Updated Fern Tree of Life |journal=Frontiers in Plant Science |volume=13 |issue= |page= 909768| doi=10.3389/fpls.2022.909768 |pmid= 36092417|pmc= 9449725|bibcode= 2022FrPS...1309768N|doi-access=free}}</ref> and Fern Tree of life<ref>{{cite web|last1= |first1= |last2= |display-authors=et al. |year=2024 |title=Tree viewer: interactive visualization of FTOL |url=https://fernphy.github.io/viewer.html |version=FTOL v1.7.0 [GenBank release 261] |access-date=1 May 2025}}</ref>
|- 
| style="vertical-align:top|
{{Clade | style=font-size:90%;line-height:80%
|label1=''Equisetum''
|1={{clade
  |1={{clade
  |label1=(''Paramochaete'')
  |1=[[Equisetum bogotense|''E. bogotense'']]
     }}
  |2={{clade
    |label1=(''Equisetum'')
    |1={{clade
      |1={{clade
        |1=[[Equisetum palustre|''E. palustre'']]
        |2=[[Equisetum pratense|''E. pratense'']]
         }}
      |2={{clade
        |1={{clade
          |1=[[Equisetum telmateia|''E. telmateia'']]
          |2=[[Equisetum braunii|''E. braunii'']]
           }}
        |2={{clade
          |1=[[Equisetum sylvaticum|''E. sylvaticum'']]
          |2={{clade
            |1={{clade
              |1=[[Equisetum diffusum|''E. diffusum'']]
              |2=[[Equisetum fluviatile|''E. fluviatile'']]
               }}
            |2=[[Equisetum arvense|''E. arvense'']]
             }}
           }}
         }}
       }}
    |label2=(''Hippochaete'')
    |2={{clade
      |1=[[Equisetum scirpoides|''E. scirpoides'']]
      |2={{clade
        |1=[[Equisetum variegatum|''E. variegatum'']]
        |2={{clade
          |1={{clade
            |1=[[Equisetum ramosissimum|''E. ramosissimum'']]
            |2={{clade
              |1=[[Equisetum hyemale|''E. hyemale'']]
              |2=[[Equisetum praealtum|''E. praealtum'']]
               }}
             }}
          |2={{clade
            |1={{clade
              |1=[[Equisetum laevigatum|''E. laevigatum'']]
              |2=[[Equisetum myriochaetum|''E. myriochaetum'']]
               }}
            |2=[[Equisetum giganteum|''E. giganteum'']]
             }}
           }}
         }}
       }}
     }}
   }}
}}
|
{{Clade | style=font-size:90%;line-height:80%
|label1=''Equisetum''
|1={{clade
  |1={{clade
  |label1=(''Paramochaete'')
  |1=''[[Equisetum bogotense|E. bogotense]]''
     }}
  |2={{clade
    |label1=(''Equisetum'')
    |1={{clade
      |1={{clade
        |1=''[[Equisetum × fontqueri|E. × fontqueri]]''
        |2=''[[Equisetum telmateia|E. telmateia]]''
         }}
      |2={{clade
        |1=''[[Equisetum pratense|E. pratense]]''
        |2={{clade
          |1=''[[Equisetum palustre|E. palustre]]''
          |2={{clade
            |1={{clade
              |1=''[[Equisetum × dycei|E. × dycei]]''
              |2=''[[Equisetum fluviatile|E. fluviatile]]''
               }}
            |2={{clade
              |1=''[[Equisetum arvense|E. arvense]]''
              |2={{clade
                |1=''[[Equisetum × litorale|E. × litorale]]''
                |2=''[[Equisetum sylvaticum|E. sylvaticum]]''
                 }}
               }}
             }}
           }}
         }}
       }}
    |label2=(''Hippochaete'')
    |2={{clade
      |1={{clade
        |1=''[[Equisetum giganteum|E. giganteum]]''
        |2=''[[Equisetum × schaffneri|E. × schaffneri]]''
          }}
      |2={{clade
        |1={{clade
          |1=''[[Equisetum myriochaetum|E. myriochaetum]]''
          |2={{clade
            |1=''[[Equisetum × ferrissii|E. × ferrissii]]''
            |2=''[[Equisetum laevigatum|E. laevigatum]]''
             }}
           }}
        |2={{clade
          |1={{clade
            |1=''[[Equisetum scirpoides|E. scirpoides]]''
            |2=''[[Equisetum ramosissimum|E. ramosissimum]]''
             }}
          |2={{clade
            |1=''[[Equisetum variegatum|E. variegatum]]''
            |2={{clade
              |1=''[[Equisetum hyemale|E. hyemale]]''
              |2=''[[Equisetum × trachyodon|E. × trachyodon]]''
               }}
             }}
           }}
         }}
       }}
     }}
   }}
}}
|}

==Distribution and ecology==
The genus ''Equisetum'' as a whole, while concentrated in the non-tropical northern hemisphere, is near-[[cosmopolitan distribution|cosmopolitan]], being absent naturally only from [[Antarctica]], [[Australia]], [[New Zealand]], and the islands of the [[Pacific Ocean]]. They are most common in northern Europe, with ten species (''E.&nbsp;arvense'', ''E.&nbsp;fluviatile'', ''E.&nbsp;hyemale'', ''E.&nbsp;palustre'', ''E.&nbsp;pratense'', ''E.&nbsp;ramosissimum'', ''E.&nbsp;scirpoides'', ''E.&nbsp;sylvaticum'', ''E.&nbsp;telmateia'', and ''E.&nbsp;variegatum''); [[Great Britain]] has nine of these species, missing only ''E.&nbsp;scirpoides'' of the European list.<ref name="Fitter">{{cite book |last1=Fitter |first1=Richard |last2=Fitter |first2=Alastair |last3=Farrer |first3=Anne |title=Collins Guide to the Grasses, Sedges, Rushes and Ferns of Britain and Northern Europe |date=1984 |publisher=Collins |location=London |isbn=0-00-219136-9 |pages=188–191}}</ref><ref name = Streeter/> Northern North America (Canada and the northernmost United States), also has nine species (''E.&nbsp;arvense'', ''E.&nbsp;fluviatile'', ''E.&nbsp;laevigatum'', ''E.&nbsp;palustre'', ''E.&nbsp;praealtum'', ''E.&nbsp;pratense'', ''E.&nbsp;scirpoides'', ''E.&nbsp;sylvaticum'', and ''E.&nbsp;variegatum''). Only five (''E.&nbsp;bogotense'', ''E.&nbsp;giganteum'', ''E.&nbsp;myriochaetum'', ''E.&nbsp;ramosissimum'', and ''E.&nbsp;xylochaetum'') of the eighteen species are known to be native south of the Equator.

They are [[perennial plant]]s, [[Herbaceous plant|herbaceous]] and dying back in winter in most temperate species, or [[evergreen]] as most tropical species and the temperate species ''[[Equisetum hyemale|E.&nbsp;hyemale]]'' (rough horsetail), ''[[Equisetum ramosissimum|E.&nbsp;ramosissimum]]'' (branched horsetail), ''[[Equisetum scirpoides|E.&nbsp;scirpoides]]'' (dwarf horsetail) and ''[[Equisetum variegatum|E.&nbsp;variegatum]]'' (variegated horsetail). They typically grow 20&nbsp;cm–1.5&nbsp;m (8&nbsp;in–5&nbsp;ft) tall, though the subtropical "giant horsetails" are recorded to grow as high as {{cvt|5|m|ft|0}} (''[[Equisetum giganteum|E.&nbsp;giganteum]]'', southern giant horsetail) or {{cvt|8|m|ft|0}} (''[[Equisetum myriochaetum|E.&nbsp;myriochaetum]]'', Mexican giant horsetail), and allegedly even more.<ref>{{cite web |last1=Husby |first1=Chad E. |title=How large are the giant horsetails? |url=http://www.fiu.edu/~chusb001/GiantEquisetum/HowLarge.html |website=The Giant Horsetails |access-date=20 November 2008 |archive-url=https://web.archive.org/web/20040411005228/http://www.fiu.edu/~chusb001/GiantEquisetum/HowLarge.html |archive-date=11 April 2004 |date=2003}}</ref>

One species, ''[[Equisetum fluviatile]]'', is an emergent [[Aquatic plant|aquatic]], rooted in water with shoots growing into the air. The stalks arise from [[rhizome]]s that are deep underground and difficult to dig out. Field horsetail (''[[Equisetum arvense|E.&nbsp;arvense]]'') can be a nuisance [[weed]], readily regrowing from the rhizome after being pulled out. It is unaffected by many [[herbicide]]s designed to kill [[Spermatophyte|seed plants]].<ref>{{cite web|url=https://oregonstate.edu/dept/nursery-weeds/weedspeciespage/horsetail/Equisetum_arvense_horsetail.html|title=Horsetail - 'Equisetum arvense'|date=2003|first=James|last=Altland|access-date=2019-07-17|website=oregonstate.edu|archive-date=2018-11-14|archive-url=https://web.archive.org/web/20181114181423/http://oregonstate.edu/dept/nursery-weeds/weedspeciespage/horsetail/Equisetum_arvense_horsetail.html|url-status=dead}}</ref>{{citation needed|date=August 2016}} Since the stems have a waxy coat, the plant is resistant to contact weedkillers like glyphosate.<ref>{{cite web|title=Control Horse or Mare's Tail - Equisetum Arvense|url=https://www.allotment-garden.org/gardening-information/weed-control/control-horse-mares-tail-equisetum-arvense/|department=Controlling Horsetail with Contact Herbicides|date=2016|website=allotment-garden.org|access-date=2019-07-17}}</ref> However, as ''E.&nbsp;arvense'' prefers an acid soil, [[Agricultural lime|lime]] may be used to assist in eradication efforts to bring the [[soil pH]] to 7 or 8.<ref>{{cite web |last1=Kress |first1=Henriette |title=Getting rid of horsetail |url=https://www.henriettes-herb.com/blog/getting-rid-horsetail.html |website=Henriette's Herbal Homepage |access-date=19 May 2010 |date=7 April 2005}}</ref> Members of the genus have been declared noxious weeds in [[Australia]] and in the US state of [[Oregon]].<ref name=aus>{{cite book|title=Noxious weeds of Australia|url=https://books.google.com/books?id=sRCrNAQQrpwC&q=Equisetum%20australia&pg=PA14|publisher=CSIRO Publishing |year=2001|page=14|author1=William Thomas Parsons |author2=Eric George Cuthbertson |isbn=978-0-643-06514-7}}</ref><ref>{{cite web|title=''Equisetum telmateia'' Ehrh. giant horsetail|url=http://plants.usda.gov/java/profile?symbol=EQTE|publisher=[[USDA]]|access-date=2010-05-18}}</ref>

All the ''Equisetum'' are classed as "unwanted organisms" in [[New Zealand]] and are listed on the [[National Pest Plant Accord]].<ref>{{cite web|title=National Pest Plant Accord|url=http://www.rnzih.org.nz/pages/accord.pdf|date=2001|website=rnzih.org.nz|access-date=2019-07-17}}</ref>

==Consumption==
People have regularly consumed horsetails. The fertile stems bearing strobili of some species can be cooked and eaten like asparagus<ref>{{cite web |title=Equisetum (PFAF Plant Database) |url=https://pfaf.org/user/Plant.aspx?LatinName=Equisetum |website=Plants For A Future}}</ref> (a dish called {{nihongo||土筆|tsukushi}} in [[Japan]]<ref>{{cite book |last1=Ashkenazi |first1=Michael |last2=Jacob |first2=Jeanne |title=Food culture in Japan |date=2003 |publisher=Greenwood Press |location=Westport, CT |isbn=0-313-32438-7}}</ref>{{Failed verification|date=August 2021}}). Indigenous nations across [[Pacific Northwest|Cascadia]] consume and use horsetails in a variety of ways, with the [[Squamish people|Squamish]] calling them ''sx̱ém'x̱em'' and the [[List of Lushootseed-speaking peoples|Lushootseed]] using ''gʷəɫik'', or horsetail roots, for cedar root baskets.<ref>{{cite book |last1=Turner |first1=Nancy J. |title=Ancient Pathways, Ancestral Knowledge. Ethnobotany and Ecological Wisdom of Indigenous Peoples of Northwestern North America |date=2014 |publisher=McGill-Queen’s University Press |isbn=978-0773543805 |url=https://dspace.library.uvic.ca/bitstream/handle/1828/5091/Appendix%202B%20%20UVicSpace%20Indigenous%20names%20of%20native%20species_BIG.pdf |chapter=Appendix 2B. Names of Native Plant Species in Indigenous Languages of Northwestern North America}}</ref><ref>{{cite book |last1=Gunther |first1=Erna |title=Ethnobotany of western Washington: the knowledge and use of indigenous plants by Native Americans |date=1973 |publisher=University of Washington Press |location=Seattle, WA |isbn=9780295952581 |edition=Revised}}</ref><ref>{{cite web |last1=Hartford |first1=Robin |title=Is Field Horsetail Edible? |url=https://www.eatweeds.co.uk/field-horsetail-edible |website=Eatweeds|date=25 March 2017 }}</ref> The young plants are eaten cooked or raw, but considerable care must be taken.<ref name=drugs/>

If eaten over a long enough period of time, some species of horsetail can be [[poison]]ous to grazing animals, including [[List of plants poisonous to equines|horses]].<ref>{{cite book |last1=Israelsen |first1=Clark E. |last2=McKendrick |first2=Scott S. |last3=Bagley |first3=Clell V. |title=Poisonous Plants and Equine |date=2010 |publisher=[[Utah State University]] |location=Logan, UT |page=6 |edition=Revised |url=https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1117&context=extension_curall}}</ref> The toxicity appears to be due to [[thiaminase]], which can cause thiamin (vitamin B1) deficiency.<ref name="drugs">{{cite web|title=Horsetail|url=https://www.drugs.com/npp/horsetail.html|publisher=Drugs.com|access-date=19 August 2018|date=11 June 2018}}</ref><ref name=NIH/><ref name=Henderson>{{cite journal |vauthors=Henderson JA, Evans EV, McIntosh RA |title=The antithiamine action of ''Equisetum'' |journal=Journal of the American Veterinary Medical Association |volume=120 |issue=903 |pages=375–8 |date=June 1952 |pmid=14927511}}</ref><ref name=Fabre>{{cite journal|last1=Fabre|first1=B|last2=Geay |first2=B. |last3=Beaufils |first3=P. |title=Thiaminase activity in ''Equisetum arvense'' and its extracts.|journal=Plant Med Phytother|year=1993|volume=26|pages=190–7}}</ref>

''Equisetum'' species may have been a common food for herbivorous dinosaurs.  With studies showing that horsetails are nutritionally of high quality, it is assumed that horsetails were an important component of herbivorous dinosaur diets.<ref>{{cite web |author1=University of Bonn |author1-link=University of Bonn |title=How Did Huge Dinosaurs Find Enough Food? Did Bacteria Aid Their Digestion? |url=https://www.sciencedaily.com/releases/2008/02/080206105443.htm |website=ScienceDaily |date=12 February 2018}}</ref> Analysis of the scratch marks on hadrosaur teeth is consistent with grazing on hard plants like horsetails.<ref name=WillBarrPurn09>{{Citation |last1=Williams |first1=Vincent S. |last2=Barrett |first2=Paul M. |last3=Purnell |first3=Mark A. |date=2009 |title=Quantitative analysis of dental microwear in hadrosaurid dinosaurs, and the implications for hypotheses of jaw mechanics and feeding |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=27 |pages=11194–11199 |doi=10.1073/pnas.0812631106 |doi-access=free |pmid=19564603 |name-list-style=amp |pmc=2708679 |bibcode=2009PNAS..10611194W }}</ref>

==Folk medicine and safety concerns==
Extracts and other preparations of ''E.&nbsp;arvense'' have served as [[traditional medicine|herbal remedies]], with records dating over centuries.<ref name=drugs/><ref name="NIH">{{cite web |url=https://www.nlm.nih.gov/medlineplus/druginfo/natural/843.html|title=Horsetail|publisher=MedlinePlus, US National Library of Medicine, National Institutes of Health|date=8 December 2017|access-date=14 November 2013}}</ref><ref name="sarris">{{cite journal|pmc=5295114|year=2017|last1=Dragos|first1=D|title=Phytomedicine in Joint Disorders|journal=Nutrients|volume=9|issue=1|pages=70|last2=Gilca|first2=M|last3=Gaman|first3=L|last4=Vlad|first4=A|last5=Iosif|first5=L|last6=Stoian|first6=I|last7=Lupescu|first7=O|doi=10.3390/nu9010070|pmid=28275210|doi-access=free}}</ref> In 2009, the [[European Food Safety Authority]] concluded there was no evidence for the supposed [[health claim|health effects]] of ''E.&nbsp;arvense'', such as for invigoration, weight control, skincare, hair health or bone health.<ref name ="efsa">{{Cite journal|title=Scientific opinion on the substantiation of health claims related to ''Equisetum arvense'' L. and invigoration of the body (ID 2437), maintenance of skin (ID 2438), maintenance of hair (ID 2438), maintenance of bone (ID 2439), and maintenance or achievement of a normal body weight (ID 2783) pursuant to Article 13 of Regulation (EC) No 1924/2006|journal=EFSA Journal|volume=7|issue=10|pages=1289|publisher=[[European Food Safety Authority]]|doi=10.2903/j.efsa.2009.1289|year=2009|doi-access=free}}</ref> {{As of|2018}}, there is insufficient scientific evidence for its effectiveness as a medicine to treat any human condition.<ref name=drugs/><ref name=sarris/><ref name=efsa/>

''E.&nbsp;arvense'' contains [[thiaminase]], which metabolizes the [[B vitamins|B vitamin]], [[thiamine]], potentially causing [[thiamine deficiency]] and associated [[hepatotoxicity|liver damage]], if taken chronically.<ref name=drugs/><ref name=NIH/> Horsetail might produce a [[diuresis|diuretic effect]].<ref name=drugs/><ref name=NIH/> Further, its safety for oral consumption has not been sufficiently evaluated and it may be [[toxicity|toxic]], especially to children and pregnant women.<ref name=drugs/>

==See also==
* [[List of plants poisonous to equines]]
{{Clear}}

==References==
{{Reflist|2}}

==Further reading==
* {{cite journal |last1=Husby |first1=Chad E. |last2=Walkowiak |first2=Radosław J. |editor1-last=Zawada |editor1-first=Beth |title=An Introduction to the Genus ''Equisetum'' (Horsetail) and the Class Equisetopsida (Sphenopsida) as a whole |journal=IEA Paper |date=2012 |url=https://internationalequisetologicalassociation.yolasite.com/resources/IEA-Paper-2012.pdf |publisher=International Equisetological Association}}
* {{cite journal |last1=Weber |first1=Reinhard |title=''Equisetites aequecaliginosus'' sp. nov., ein Riesenschachtelhalm aus der spättriassischen Formation Santa Clara, Sonora, Mexiko |journal=Revue de Paléobiologie |date=June 2005 |volume=24 |issue=1 |pages=331–364 |url=https://www.ville-ge.ch/mhng/paleo/paleo-pdf/24-1/pal-24-1-16.pdf |trans-title=''Equisetites aequecaliginosus'' sp. nov., a giant horsetail from the late Triassic Santa Clara Formation, Sonora, Mexico |publisher=[[Natural History Museum of Geneva|Muséum d'histoire naturelle]] |location=Geneva, Switzerland |language=de,en |issn=1661-5468 |archive-url=https://web.archive.org/web/20160327011716/http://www.ville-ge.ch/mhng/paleo/paleo-pdf/24-1/pal-24-1-16.pdf |archive-date=27 March 2016 |access-date=26 August 2021 |url-status=live }}
* {{cite web | last=Teichman | first=Rachel | title=The Ancient (Native) Horsetail: Sometimes Unwelcomed, Always Fascinating! – SSISC | website=SSISC – [[Sea to Sky (disambiguation)|Sea to Sky]] Invasive Species Council | date=2021-08-03 | url=http://ssisc.ca/horsetail | access-date=2021-08-06}}

==External links==
{{Commons category|Equisetum}}
* [http://tolweb.org/Equisetum/33130/ ''Equisetum''] at the Tree of Life Web Project
* [http://equisetum.org/ National Collection of ''Equisetum'']
* [http://internationalequisetologicalassociation.yolasite.com/ International Equisetological Association]
* {{Cite EB1911|wstitle=Horsetail|short=x}}

{{Plant classification}}
{{Fern classification}}
{{Taxonbar|from=Q28114}}
{{Authority control}}
[[Category:Equisetum| ]]
[[Category:Fern genera]]
[[Category:Medicinal plants]]
[[Category:Extant Middle Jurassic first appearances]]
[[Category:Callovian first appearances]]
[[Category:Callovian genus first appearances]]
[[Category:Taxa named by Carl Linnaeus]]