Equisetum

Equisetaceae
Fossil range: Late Devonian-Recent
375.0–0 Ma
"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
Genera

Equisetum
and see text

Equisetum (pronounced /ˌɛkwɨˈsiːtəm/) (horsetail, snake grass, puzzlegrass) is the only living genus in the Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds. )[1]

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;[2] the genus Calamites of 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 and misnamed as "horsetail".

Contents

Etymology

Microscopic view of Rough Horsetail, Equisetum hyemale (2-1-0-1-2 is one millimeter with 1/20th graduation).
The small white protuberances are accumulated silicates on cells.

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 scouring-rush for unbranched or sparsely branched individuals. The latter name refers to the plants' rush-like appearance, 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. 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 mostly 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[3].

Many plants 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.[4] Members of the genus have been declared noxious weeds in Australia and in the US state of Oregon.[5][6]

Vegetative stem:
B = branch in whorl
I = internode
L = leaves
N = node

If eaten in large quantities, the foliage of some species is poisonous to grazing animals, including (somewhat ironically given its common name) horses[7]. On the other hand, the young fertile stems bearing strobili of some species are cooked and eaten by humans in Japan, although considerable preparation is required and care should be taken.[8] The dish is similar to asparagus and is called tsukushi.[9] The people of ancient Rome would also eat meadow horsetail in this manner, but they also used it to make tea as well as a thickening powder.[10] Indians of the North American Pacific Northwest eat the young shoots of this plant raw.[11] The leaves 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 voracious ability to take up the metal when it is in a solution.[10]

Anatomy

Strobilus of Northern Giant Horsetail (Equisetum telmatei braunii), terminal on an unbranched stem.

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 primitive like in Lycopodiophyta (clubmosses and relatives), but rather advanced adaptations, evolved by the reduction of a megaphyll[12]. They are therefore sometimes actually referred to as megaphylls to reflect this homology.

The leaves of horsetails grow in whorls fused into nodal sheaths. The stems are green and photosynthetic, and distinctive in being hollow, jointed and ridged (with sometimes 3 but usually 6-40 ridges) and these are often played with by children who will separate and then seamlessly rejoin the segments. There may or may not be whorls of branches at the nodes; when present, these branches are identical to the main stem except being smaller and more delicate.

Spores

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 stems are unbranched, and in some (e.g. field horsetail, E. arvense) they are non-photosynthetic, produced early in spring separately from photosynthetic sterile stems. In some other species (e.g. marsh horsetail, E. palustre) they are very similar to sterile stems, 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.

Evolution and systematics

The Equisetopsida were formerly regarded as a separate division of spore plants and also called Equisetophyta, Arthrophyta or Sphenophyta; today they have been recognized as rather close relatives of the typical ferns (Pteridopsida) and form a specialized lineage of the Pteridophyta.[13] Pseudobornia is the oldest known relative of Equisetum; it grew in the late Devonian, about 375 million years ago and is assigned to its own order.

As mentioned above, all living horsetails are placed in the genus Equisetum. But there are some fossil species that are not assignable to the modern genus:

Species

The living members of the genus Equisetum are divided into two distinct lineages, which are treated as subgenera. Hybridogenic species are common, but such hybridization has only been recorded between members of the same subgenus.[15]

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

Kamchatka Horsetail in Parc floral de Paris
Subgenus Equisetum
Branched Horsetail (E. ramosissimum)
Subgenus Hippochaete

Named hybrids

Equisetum × moorei (Rough Horsetail × Branched Horsetail)
Hybrids between species in subgenus Equisetum
Hybrids between species in subgenus Hippochaete

Equisetum cell walls

The crude cell extracts of all Equisetum species tested contain mixed-linkage glucan : xyloglucan endotransglucosylase (MXE) activity[16]. 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.[17][18] 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.[19] The European Food Safety Authority issued a report assessing its medicinal uses in 2009.[20] Research has confirmed its action as an anti-oxidant.[21]

See also

Footnotes

  1. ↑ Sunset Western Garden Book, 1995:606–607
  2. ↑ "An Introduction to the Genus Equisetum and the Class Sphenopsida as a whole". Florida International University. http://www.fiu.edu/~chusb001/GiantEquisetum/Intro_Equisetum.html. Retrieved 2009-07-22. 
  3. ↑ Husby (2003)
  4. ↑ Kress, Henriette, Getting rid of horsetail, Henriette's Herbal Homepage, April 7th, 2005. Retrieved May 19, 2010.
  5. ↑ William Thomas Parsons, Eric George Cuthbertson (2001). Noxious weeds of Australia. Csiro Publishing. p. 14. ISBN 9780643065147. http://books.google.com/?id=sRCrNAQQrpwC&pg=PA14&dq=Equisetum+australia&q=Equisetum%20australia. 
  6. ↑ "Equisetum telmateia Ehrh. giant horsetail". USDA. http://plants.usda.gov/java/profile?symbol=EQTE. Retrieved 2010-05-18. 
  7. ↑ Israelsen et al. (2006)
  8. ↑ Plants For A Future: Equisetum arvense.
  9. ↑ Michael Ashkenazi, Jeanne Jacob. 2003. Food culture in Japan. Greenwood Publishing Group. 232 p.
  10. ↑ 10.0 10.1 Plants of the Pacific Northwest Coast: Washington, Oregon, British Columbia & Alaska, Written by Paul Alaback, ISBN 978-1-55105-530-5
  11. ↑ Erna Gunther. 1973. Ethnobotany of western Washington: The knowledge and use of indigenous plants by Native Americans.
  12. ↑ Rutishauser (1999)
  13. ↑ Pryer et al. (2004), Smith et al. (2006)
  14. ↑ Weber (2005)
  15. ↑ Pigott (2001)
  16. ↑ http://www3.interscience.wiley.com/journal/120123725/abstract?CRETRY=1&SRETRY=0
  17. ↑ http://www.ncbi.nlm.nih.gov/pubmed/18393951
  18. ↑ http://www.ncbi.nlm.nih.gov/pubmed/18284587
  19. ↑ "Horsetail". University of Maryland. http://www.umm.edu/altmed/articles/horsetail-000257.htm. Retrieved 2010-05-18. 
  20. ↑ "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. http://www.efsa.europa.eu/en/scdocs/scdoc/1289.htm. Retrieved 2010-05-18. 
  21. ↑ "Exploring Equisetum arvense L., Equisetum ramosissimum L. and Equisetum telmateia L. as sources of natural antioxidants". Phytotherapy Research - Ministry of Science and Environmental Protection of the Republic of Serbia via John Wiley & Sons. http://www3.interscience.wiley.com/journal/121543728/abstract?CRETRY=1&SRETRY=0. Retrieved 2010-05-18. "The ESR signal of DMPO-OH radical adducts in the presence of Equisetum telmateia phosphate buffer (pH 7) extract was reduced by 98.9% indicating that Equisetum telmateia could be a useful source of antioxidants with huge scavenging ability." 

References

External links