Temporal range: Callovian  to Recent
|"Candocks" of the Great Horsetail (Equisetum telmateia telmateia), showing whorls of branches and the tiny dark-tipped leaves|
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. The genus Calamites of the family Calamitaceae, for example, is abundant in coal deposits from the Carboniferous period.
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.
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. Members of the genus have been declared noxious weeds in Australia and in the US state of Oregon.
If eaten over a long enough period of time, some species of horsetail can be poisonous to grazing animals, including horses. The toxicity appears to be due to thiaminase enzymes, which can cause thiamine (vitamin B1) deficiency. People have regularly consumed horsetails. The young plants are eaten cooked or raw, but considerable care must be taken. For example, the fertile stems bearing strobili of some species are cooked and eaten like asparagus (a dish called tsukushi) in Japan. 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. Indians of the North American Pacific Northwest eat the young shoots of this plant raw. 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.
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. 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.
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
- Equisetum arvense L. – Field Horsetail, Common Horsetail or Giant Horsetail
- Equisetum bogotense Kunth – Andean Horsetail or Giant Horsetail
- Equisetum diffusum L. – Himalayan Horsetail
- Equisetum fluviatile L. – Water Horsetail
- Equisetum palustre L. – Marsh Horsetail
- Equisetum pratense Ehrh. – Meadow Horsetail, Shade Horsetail, Shady Horsetail
- Equisetum sylvaticum L. – Wood Horsetail
- Equisetum telmateia Ehrh. – Great Horsetail, Northern Giant Horsetail
- Subgenus Hippochaete
- Equisetum giganteum L. – Southern Giant Horsetail or Giant Horsetail
- Equisetum myriochaetum Schltdl. & Cham. – Mexican Giant Horsetail or Giant Horsetail
- Equisetum hyemale L. – Rough Horsetail, Scouringrush Horsetail
- Equisetum laevigatum A. Braun – Smooth Horsetail
- Equisetum ramosissimum Desf. – Branched Horsetail
- Equisetum scirpoides Michx. – Dwarf Horsetail
- Equisetum variegatum Schleich. ex Weber & Mohr – Variegated Horsetail
- unplaced to subgenus
- Hybrids between species in subgenus Equisetum
- Equisetum × bowmanii C.N.Page (Equisetum sylvaticum × Equisetum telmateia)
- Equisetum × dycei C.N.Page (Equisetum fluviatile × Equisetum palustre)
- Equisetum × font-queri Rothm. (Equisetum palustre × Equisetum telmateia)
- Equisetum × litorale Kühlew ex Rupr. (Equisetum arvense × Equisetum fluviatile)
- Equisetum × mchaffieae C.N.Page (Equisetum fluviatile × Equisetum pratense)
- Equisetum × mildeanum Rothm. (Equisetum pratense × Equisetum sylvaticum)
- Equisetum × robertsii Dines (Equisetum arvense × Equisetum telmateia)
- Equisetum × rothmaleri C.N.Page (Equisetum arvense × Equisetum palustre)
- Equisetum × willmotii C.N.Page (Equisetum fluviatile × Equisetum telmateia)
- Hybrids between species in subgenus Hippochaete
- Equisetum × ferrissii Clute (Equisetum hyemale × Equisetum laevigatum)
- Equisetum × moorei Newman (Equisetum hyemale × Equisetum ramosissimum)
- Equisetum × nelsonii (A.A.Eaton) Schaffn. (Equisetum laevigatum × Equisetum variegatum)
- Equisetum × schaffneri Milde (Equisetum giganteum × Equisetum myriochaetum)
- Equisetum × trachydon A.Braun (Equisetum hyemale × Equisetum variegatum)
Equisetum cell walls
The crude cell extracts of all Equisetum species tested contain mixed-linkage glucan : Xyloglucan endotransglucosylase (MXE) activity. 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. 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.
The plant has a long history of medicinal uses, although modern sources include cautions with regard to its use. 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.
These plants have a high content of thiaminase, which may induce edema and may cause lack of limb coordination, possibly even Falling, slow heart-rate or cardiac irregularity. It is mentioned in the fifth edition of the national pharmacopoeia of Argentina that response to treatment with thiamin is effective. Since horsetail contains traces of nicotine, it is not recommended for young children
There is insufficient evidence of its effectiveness as a medicine, but taken orally Equisetum giganteum is widely used in South America as a diuretic to reduce swelling caused by excess fluid retention and for urinary infections, bladder and kidney disorders. It also contains silicon which is why it is sometimes suggested as appropriate for sufferers from brittle bone disorders 
Dosage is a matter of conjecture, but dried herb capsules of 300 mg are sometimes recommended to be taken 3 times per day. More commonly it is prepared as an infusion whose content can only be guessed – one tablespoonful or half an ounce (c. 10g - 15g) of dried herbs mixed with 5 cup-fulls (c. 1 litre) of boiling water and when cool, drunk as tea or used as a compress
The best time to collect horsetail grass, to produce medicinal tea, compress or store for later usuage, is during the midsummer. You can use the collected shoots of the horsetail grass fresh or dried.
- "Equisetum thermale sp. nov. (Equisetales) from the Jurassic San Agustín hot spring deposit, Patagonia: anatomy, paleoecology, and inferred paleoecophysiology". American Journal of Botany 98 (4): 680–97. April 2011. doi:10.3732/ajb.1000211. PMID 21613167.
- Sunset Western Garden Book, 1995:606–607
- "An Introduction to the Genus Equisetum and the Class Sphenopsida as a whole". Florida International University. Retrieved 2009-07-22.
- Sacks, Oliver (August 2011). "Field Trip: Hunting Horsetails". The New Yorker.
- Husby, Chad E. (2003): How large are the giant horsetails? Version of 2003-03-19. Retrieved 2008-11-20.
- Kress, Henriette, Getting rid of horsetail, Henriette's Herbal Homepage, April 7th, 2005. Retrieved May 19, 2010.
- William Thomas Parsons, Eric George Cuthbertson (2001). Noxious weeds of Australia. CSIRO Publishing. p. 14. ISBN 978-0-643-06514-7.
- "Equisetum telmateia Ehrh. giant horsetail". USDA. Retrieved 2010-05-18.
- Israelsen, Clark E.; McKendrick, Scott S. & Bagley, Clell V. (2006): Poisonous Plants and Equine. PDF fulltext
- Henderson, JA; Evans EV, McIntosh RA. (June 1952). "The antithiamine action of Equisetum.". J Am Vet Med Assoc. 120 (903): 375–8. PMID 14927511. Retrieved 3 February 2013.
- Fabre, B; Geay B, Beaufils P. (1993). "Thiaminase activity in equisetum arvense and its extracts.". Plant Med Phytother 26: 190–7.
- "Horsetail". National Library of Medicine. Retrieved 3 February 2013.
- Pohl, Richard (1955). "Toxicity of ferns and equisetum". American Fern Journal 45 (3): 95–97.
- "Horsetail". University of Maryland. Retrieved 2010-05-18.
- Michael Ashkenazi, Jeanne Jacob. 2003. Food culture in Japan. Greenwood Publishing Group. 232 p.
- Plants For A Future Database.
- Plants of the Pacific Northwest Coast: Washington, Oregon, British Columbia & Alaska, Written by Paul Alaback, ISBN 978-1-55105-530-5
- Erna Gunther. 1973. Ethnobotany of western Washington: The knowledge and use of indigenous plants by Native Americans.
- Rutishauser, Rolf (1999): Polymerous Leaf Whorls in Vascular Plants: Developmental Morphology and Fuzziness of Organ Identities. International Journal of Plant Sciences 160(Supplement 6): 81–103. doi:10.1086/314221 PMID 10572024 PDF fulltext
- Pigott, Anthony (4 October 2001). "Summary of Equisetum Taxonomy". National Collection of Equisetum. Archived from the original on 21 October 2010. Retrieved 17 June 2013.
- Fry, S. C.; Mohler, K. E.; Nesselrode, B. H. W. A.; Frankov, L. (2008). "Mixed-linkage -glucan:xyloglucan endotransglucosylase, a novel wall-remodelling enzyme fromEquisetum(horsetails) and charophytic algae". The Plant Journal 55 (2): 240–252. doi:10.1111/j.1365-313X.2008.03504.x. PMID 18397375.
- Fry, Stephen C.; Nesselrode, Bertram H. W. A.; Miller, Janice G.; Mewburn, Ben R. (2008). "Mixed-linkage (1→3,1→4)-β-d-glucan is a major hemicellulose of Equisetum (horsetail) cell walls". New Phytologist 179 (1): 104–15. doi:10.1111/j.1469-8137.2008.02435.x. PMID 18393951.
- Sørensen, Iben; Pettolino, Filomena A.; Wilson, Sarah M.; Doblin, Monika S.; Johansen, Bo; Bacic, Antony; Willats, William G. T. (2008). "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". The Plant Journal 54 (3): 510–21. doi:10.1111/j.1365-313X.2008.03453.x. PMID 18284587.
- "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". European Food Safety Authority. Retrieved 2013-10-09.
- "Horsetail". Rush Foundation USA. Retrieved 14 Nov 2013.
- "Horsetail". US National Institute of Health. Retrieved 14 November 2013.
- "Medicinal Horsetail Grass". Prepper Gardens. Retrieved January 21, 2014.
- Walkowiak, Radoslaw (2008): IEA – Equisetum 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. Am. J. Bot. 91(10): 1582-1598. PDF fulltext
- Rutishauser, R. (1999). "Polymerous Leaf Whorls in Vascular Plants: Developmental Morphology and Fuzziness of Organ Identities". International Journal of Plant Sciences 160 (S6): S81–S103. doi:10.1086/314221. PMID 10572024.
- 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
|Wikimedia Commons has media related to Equisetaceae.|