Equisetum

{{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 scientific name Equisetum is derived from the Latin {{lang|la|equus}} ('horse') + {{lang|la|seta}} ('bristle').{{cite book |page= 283 |title= Florida Ethnobotany |author= Daniel F. Austin |edition=illustrated |publisher= CRC Press |year= 2004 |isbn= 9780203491881}}

Other names include candock for branching species, puzzlegrass, and snake grass or scouring-rush for unbranched or sparsely branched species. 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.{{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 }} In German, the corresponding name is {{lang|de|Zinnkraut}} ('tin-herb'). In Spanish-speaking countries, these plants are known as {{lang|es|cola de caballo}} ('horsetail').

File:Equisetum arvense 001.JPG (field horsetail)]]

Equisetum 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 lycophytes (clubmosses and relatives), but rather derived adaptations, evolved by reduction of megaphylls.{{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 }}

The leaves of horsetails are arranged in whorls fused into 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 ridges). There may or may not be whorls of branches at the nodes.Streeter D, Hart-Davies C, Hardcastle A, Cole F, Harper L. 2009. Collins Flower Guide. Harper Collins {{ISBN|9-78-000718389-0}} Unusually, the branches often emerge below the leaves in an internode, and grow from buds between their bases.

Image:Horsetail vegeative stem.JPG

Image:Equisetum braunii (strobilus), Portland, Oregon.jpg, terminal on an unbranched stem]]

Image:Microscopic view of Equisetum in Japan one 20thmm graduation.jpg (rough horsetail) (2-1-0-1-2 is one millimetre with {{frac|1|20}}th graduation).
The small white protuberances are accumulated silicates on cells.]]

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. E. arvense, field horsetail) they are non-photosynthetic, produced early in spring. In some other species (e.g. E. palustre, marsh horsetail) they are very similar to sterile shoots, photosynthetic and with whorls of branches.{{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}}{{rp|12–15}}

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 through crawling and hopping motions after the sporangia have split open longitudinally.{{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}} 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.{{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 }}

The crude cell extracts of all Equisetum species tested contain mixed-linkage glucan : xyloglucan endotransglucosylase (MXE) activity.{{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 }} 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.{{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}}{{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}} 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 XET activity and cell age led to the suggestion that XET is catalysing endotransglycosylation in controlled wall-loosening during cell expansion.{{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}} 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}}

Currently, 18 species of Equisetum are accepted by Plants of the World Online. The living members are divided into three distinct lineages, which are usually treated as 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 Greek. Hybrids are common, but hybridization has only been recorded between members of the same subgenus.{{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}}

Two Equisetum plants are sold under the names Equisetum japonicum (barred horsetail) and Equisetum camtschatcense (Kamchatka horsetail). These are both types of E. hyemale var. hyemale, although they may also be listed as separate varieties of E. hyemale.{{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 }}{{Citation needed|date=October 2016}}

Image:Equisetum hyemale 02 by Line1.jpg (rough horsetail) in Parc floral de Paris]]

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{{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}} and Equisetum laterale from the Early-Middle Jurassic of Australia.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.{{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}} Silicified remains of Equisetum thermale from the Late Jurassic of Argentina exhibit all the morphological characters of modern members of the genus.{{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}} The estimated split between Equisetum bogotense and all other living Equisetum is estimated to have occurred no later than the Early Jurassic.

• {{txil|Equisetum bogotense|Kunth}} – Andean horsetail; upland South America up to Costa Rica; includes E. rinihuense, sometimes treated as a separate species. Previously included in subg. Equisetum, but Christenhusz et al. (2019) transfer this here, as E. bogotense appears to be sister to all the remaining species in the genus.

• {{txil|Equisetum arvense|L.}} – field horsetail or common horsetail; circumboreal down through temperate zones
• {{txil|Equisetum braunii|Milde}} – northern giant horsetail, syn. E. telmateia subsp. braunii (Milde) Hauke.; west coast of North America
• {{txil|Equisetum diffusum|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|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}}

Image:Equisetum ramosissimum, Slavičín, Czech Republic.jpg in the Czech Republic]]

• {{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 (Engelm.) A.A.Eat. is now treated as a separate species {{tx|Equisetum praealtum|Raf.}}
• {{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|Schltdl. & Cham.}} – Mexican giant horsetail; from central Mexico south to Peru
• {{txil|Equisetum praealtum|Raf.}} – scouringrush horsetail, syn. E. hyemale subsp. affine (Engelm.) A.A.Eat.; temperate North America
• {{txil|Equisetum ramosissimum|Desf.}} (including E. debile) – branched horsetail; Asia, Europe, Africa, southwest Pacific islands
• {{txil|Equisetum scirpoides|Michx.}} – dwarf horsetail, dwarf scouringrush; northern (cool temperate) zones worldwide
• {{txil|Equisetum variegatum|Schleich. ex Weber & Mohr}} – variegated horsetail, variegated scouringrush; northern (cool temperate) zones worldwide, except for northeasternmost Asia
• {{txil|Equisetum xylochaetum|Mett.}} – Atacama Desert giant horsetail; southern Peru, northern Chile

• {{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

Image:Equisetum x moorei3.JPG (E. hyemale × E. ramosissiumum)]]

• Equisetum × bowmanii {{small|C.N.Page}} (Equisetum sylvaticum × Equisetum telmateia)
• Equisetum × dycei {{small|C.N.Page}} (Equisetum fluviatile × Equisetum palustre)
• Equisetum × font-queri {{small|Rothm.}} (Equisetum palustre × Equisetum telmateia)
• Equisetum × litorale {{small|Kühlew ex Rupr.}} (Equisetum arvense × Equisetum fluviatile)
• Equisetum × mchaffieae {{small|C.N.Page}} (Equisetum fluviatile × Equisetum pratense)
• Equisetum × mildeanum {{small|Rothm.}} (Equisetum pratense × Equisetum sylvaticum)
• Equisetum × robertsii {{small|Dines}} (Equisetum arvense × Equisetum telmateia)
• Equisetum × rothmaleri {{small|C.N.Page}} (Equisetum arvense × Equisetum palustre)
• Equisetum × willmotii {{small|C.N.Page}} (Equisetum fluviatile × Equisetum telmateia)

• Equisetum × ferrissii {{small|Clute}} (Equisetum hyemale × Equisetum laevigatum)
• Equisetum × moorei {{small|Newman}} (Equisetum hyemale × Equisetum ramosissimum)
• Equisetum × nelsonii {{small|(A.A.Eaton) Schaffn.}} (Equisetum laevigatum × Equisetum variegatum)
• Equisetum × schaffneri {{small|Milde}} (Equisetum giganteum × Equisetum myriochaetum)
• Equisetum × trachyodon {{small|(A.Braun) W.D.J.Koch}} (Equisetum hyemale × Equisetum variegatum)

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. They are most common in northern Europe, with ten species (E. arvense, E. fluviatile, E. hyemale, E. palustre, E. pratense, E. ramosissimum, E. scirpoides, E. sylvaticum, E. telmateia, and E. variegatum); Great Britain has nine of these species, missing only E. scirpoides of the European list.{{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}} 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). Only five (E. bogotense, E. giganteum, E. myriochaetum, E. ramosissimum, and E. xylochaetum) of the eighteen species are known to be native south of the Equator.

They are perennial plants, herbaceous and dying back in winter in most temperate species, or evergreen as most tropical species and the temperate species E. hyemale (rough horsetail), E. ramosissimum (branched horsetail), E. scirpoides (dwarf horsetail) and E. variegatum (variegated horsetail). They typically grow 20 cm–1.5 m (8 in–5 ft) tall, though the subtropical "giant horsetails" are recorded to grow as high as {{cvt|5|m|ft|0}} (E. giganteum, southern giant horsetail) or {{cvt|8|m|ft|0}} (E. myriochaetum, Mexican giant horsetail), and allegedly even more.{{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}}

One species, Equisetum fluviatile, is an emergent aquatic, rooted in water with shoots growing into the air. The stalks arise from rhizomes that are deep underground and difficult to dig out. Field horsetail (E. arvense) can be a nuisance weed, readily regrowing from the rhizome after being pulled out. It is unaffected by many herbicides designed to kill seed plants.{{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}}{{citation needed|date=August 2016}} Since the stems have a waxy coat, the plant is resistant to contact weedkillers like glyphosate.{{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}} 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.{{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}} Members of the genus have been declared noxious weeds in Australia and in the US state of Oregon.{{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}}{{cite web|title=Equisetum telmateia Ehrh. giant horsetail|url=http://plants.usda.gov/java/profile?symbol=EQTE|publisher=USDA|access-date=2010-05-18}}

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

People have regularly consumed horsetails. The fertile stems bearing strobili of some species can be cooked and eaten like asparagus{{cite web |title=Equisetum (PFAF Plant Database) |url=https://pfaf.org/user/Plant.aspx?LatinName=Equisetum |website=Plants For A Future}} (a dish called {{nihongo||土筆|tsukushi}} in Japan{{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}}{{Failed verification|date=August 2021}}). Indigenous nations across Cascadia consume and use horsetails in a variety of ways, with the Squamish calling them sx̱ém'x̱em and the Lushootseed using gʷəɫik, or horsetail roots, for cedar root baskets.{{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}}{{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}}{{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 }} The young plants are eaten cooked or raw, but considerable care must be taken.

If eaten over a long enough period of time, some species of horsetail can be poisonous to grazing animals, including horses.{{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}} The toxicity appears to be due to thiaminase, which can cause thiamin (vitamin B1) deficiency.{{cite web|title=Horsetail|url=https://www.drugs.com/npp/horsetail.html|publisher=Drugs.com|access-date=19 August 2018|date=11 June 2018}}{{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}}{{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}}

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.{{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}} Analysis of the scratch marks on hadrosaur teeth is consistent with grazing on hard plants like horsetails.{{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 }}

Extracts and other preparations of E. arvense have served as herbal remedies, with records dating over centuries.{{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}}{{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}} In 2009, the European Food Safety Authority concluded there was no evidence for the supposed health effects of E. arvense, such as for invigoration, weight control, skincare, hair health or bone health.{{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}} {{As of|2018}}, there is insufficient scientific evidence for its effectiveness as a medicine to treat any human condition.

E. arvense contains thiaminase, which metabolizes the B vitamin, thiamine, potentially causing thiamine deficiency and associated liver damage, if taken chronically. Horsetail might produce a diuretic effect. Further, its safety for oral consumption has not been sufficiently evaluated and it may be toxic, especially to children and pregnant women.

• List of plants poisonous to equines

{{Clear}}

{{Reflist|2}}

• {{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=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 Invasive Species Council | date=2021-08-03 | url=http://ssisc.ca/horsetail | access-date=2021-08-06}}

{{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: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