Botanical Name: Equisetum arvense, Equisetaceae

Common names: Horsetail, Field Horsetail, Mares tail, Horse Pipes, Snake Grass, Scouring Weed, Shavegrass

Similar species: E. sylvaticum, E. pratense, E. palustre

Plant description: Horsetail is a descendant of ancient plants that grew as tall as trees during the carboniferous period of prehistoric times, and contributed significantly to the formation of modern day coal deposits.  Today however, the horsetails are comparatively smaller, although some species such as Giant Horsetail (Equisetum telmatiea) can attain a height of up to 3 m.  Horsetail is a tracheophyte, spreading not by flower and seed, but by spores and an extensive network of creeping rhizomes. It produces two types of hollow stems that grow from deep rootstocks. The leafless or fertile stems are light brown in color, about 30 cm high with a spore-bearing cone at the top of the stem, up to 3 cm long. These fertile stems emerge in early spring and die back soon after the spores are shed. The sterile, photosynthetic stems reach a height up to 70 cm, producing whorls of green, four-angled leaf-like branches that form at the joints of the stem. They begin their growth as the fertile stems are beginning to disappear in early spring, survive throughout the year until the first hard frost. Horsetail is serviced by small tubers that store energy, as well as an extensive system of creeping rhizomes that can penetrate more than 2 m into the soil.  

Habitat, ecology and distribution: Like its giant ancestors, the various species of Horsetail typically thrive in acidic, wet, poorly drained areas, preferring sunny locations, in grasslands, wet meadows, streams and other places where the water table is high. It is not opposed to more adverse conditions however, and can appear to be quite 'weedy,' growing along roadsides and in ditches, in orchards and gardens, and along railway tracks and beaches.  Horsetail is very common in temperate regions in the northern hemisphere, and some very similar species have been found in Australia.  Horsetail apparently responds well to high potassium in the soil, and is considered to be an invasive weed in modern agriculture where there is a reliance on NPK fertilizers. The fertile stems yield tiny sporelings that are viable for a very short time after being released, preferably into damp soil, and thus because of the use of herbicides on cultivated land Horsetail spreads primarily by through rhizomatous growth.

Part used: aerial parts.

History: Horsetail has long been valued by traditional peoples both as food and medicine, and as its name 'Scourweed' suggests, to scour dirty pots, wood, and certain metals like aluminum, copper and pewter.  The ancient Romans used to pick the young fertile shoots and eat them as asparagus.  The Latin genus name Equisetum is derived from 'horse' (equus) and 'tail' (setum).

Constituents: Horsetail is often cited as a good source of a variety of macro and trace minerals, containing upwards of 15% in total, especially silica (SO2), found primarily as silicates and silicic acid, but including silica as an inorganic constituent.  Other mineral constituents include calcium, magnesium, iron, potassium, manganese and aluminum.  Horsetail however does contain other potentially interesting constituents such as glycosides, phenolic acids and phytosterols.  Among the glycosides of interest are flavonols such as quercitin, kaempferol and apigenin.  The phenolic acids include di-E-caffeoyl-meso-tartaric acid and the methyl esters of protocatechuic and caffeic acids (Bradley et al 1992, 92).

Medical Research:
•Connective tissue: Silica (SiO2) is an important constituent in connective tissues such as bone, cartilage and collagen, and is found in particular in the protein elastin, which provides for the strength and integrity of tissues such as arteries, hair, skin and nails (Bergner 1997, 168).
•Urinary tract: Chloroform extracts of Equisetum fluviatile, E. hiemale var. affine, E. giganteum and E. myriochaetum were studied to determine diuretic activity in CD1 strain mice using hydrochlorothiazide, spironolactone and furosemide as standard drugs for comparison. It was found that the most active plant was E. hiemale var. affine, followed by E. fluviatile, E. giganteum and E. myriochaetum, producing an effect similar to that of hydrochlorothiazide in relation to the excretion of sodium, potassium and chloride (Perez et al 1985).  Bradley et al mention a German study that indicated that this diuretic effect occurs with the excretion of electrolytes (1992, 93)
•Cardiovascular: In an experimental study of rats fed a diet of Equisetum hyemale and hyperlipidemic foods, E. hyemale was shown to inhibit the elevation of serum triglyceride and cholesterol (Xu et al 1993).
•Diabetes: A single oral administration of a water extract of Equisetum myriochaetum at doses of 7 and 13 mg/kg, and of the butanol extract (BE) at doses of 8 and 16 mg/kg, significantly lowered the plasma glucose levels in streptozotocin-induced diabetic rats within three hours of administration. Three kaempferol glucosides and one caffeoyl glucoside were isolated from the drug and were shown to be the main constituents in both extracts (Andrade Cetto et al 2000). A single dose of a water extract of Equisetum myriochaetum was administered orally in 11 recently diagnosed type 2 diabetic patients. Glucose and insulin were measured at 0, 30, 60, 90,120 and 180 min after administration. The same patients served as the control group and received only colored water as placebo. The administration of the extract was shown to significantly reduce the blood glucose levels of the type 2 diabetic patients within 90, 120 and 180 min. There were no significant changes in the insulin levels (Revilla et al 2002).
•Ulcers: A decoction and methanol extract was prepared from the aerial parts of Equisetum palustre and tested for its effects on ethanol-induced gastric ulcer model in rats. The extract clearly demonstrated significant stomach protection against ulcerogenesis (Gubuz at al 2002).
•Immune system: Bradley et al reports that Horsetail promotes a mild leucocytosis, suggesting a mild immunostimulant activity (1992, 92).

Toxicity: One toxicity study on E. hyemale demonstrated the safety of Horsetail in rats (Xu CF et al 1993), but other studies have shown that an alkaloid in E. palustre contains a toxic alkaloid called palustrin (Bradley et al 1992, 93). No toxicity data for E. arvense could be found. Horsetail however but has displayed signs of toxicity in horses eating hay containing more that 20% Horsetail, causing progressive symptoms of weakness, staggering, nervousness, poor vision, muscular weakness and constipation.  Fatalities can occur, but the immediate removal of contaminated food brings about rapid recovery. Several substances have been associated with these effects, but the specific agent in 'equisetosis' is thought to be thiaminase, possibly in conjunction with other compounds. Cattle, sheep, and goats are rarely affected (Doll 2002).

Herbal action: connective tissue trophorestorative, vulnerary, styptic, astringent, diuretic, immunostimulant

Indications: arthritis, musculoskeletal injury, hay fever, tuberculosis, bladder infection and irritation, incontinence, edema, renal calculi, menorrhagia, intestinal hemorrhage

Contraindications and cautions: cardiac and renal failure (Bradley et al 1992, 93).

Medicinal uses: Horsetail is an important remedy in connective tissue deficiency, evidenced by dry mucus membranes, broken fingernails, split-ends, and hair loss.  This benefit however appears to extend to all types of connective tissues, including weak or damaged joints and bones, atherosclerosis and varicosities.  Horsetail is trophorestorative to mucous membranes, and is particularly indicated in dryness with chronic irritation.  This activity however extends itself to atonic states as well, astringing tissues and promoting the processing and discharge of metabolic wastes through the lymphatic system and kidneys. The usefulness of Horsetail on the mucosa is evidenced by its efficacy in respiratory conditions such as hay fever as well as in consumptive conditions of the lungs, to issues such as chronic bladder infections.  Horsetail is especially indicated in chronic joint problems and frequent musculoskeletal injuries, which tend to indicate an overall trophic deficiency of the skeletal system.  Herbalist Matthew Wood states that Horsetail is particularly indicated in poor self-esteem, where individuals tend to wait in the background of life, fearful of the repercussions of their actions, instead chewing their fingernails or plucking out their hairs "…one by one" (Wood 1997, 254).  Although the rich silica content of Horsetail has been suggested as the reason for its benefit in such conditions, it is used in very a similar way in homeopathy, and in biodynamic farming as an aqueous spray to strengthen crops from wind and rain.  The fibrous, jointed stems of Horsetail, and its jointed leaves seem to suggest the skeletal system.  Similarly, its usage as a scouring brush seems to indicate resilience.  Thus Horsetail is like an archaic memory of physical structure and strength, and has been observed to have an energetic influence to reestablish this property in the body.  The physiomedicalists and eclectics thought of Horsetail as an important kidney remedy, used in incontinence, nocturia, edema, suppression of urine, hematuria, gravel, and nephritic affections, with or without tenesmus, as well as in STDs such as gonorrhoea (Felter and Lloyd 1893).  Felter and Lloyd also mention that the ashes are used in hyperchlorhydria (1893).  Culpepper mentions its virtues in hemorrhages and indolent ulcers, Moore suggesting its usefulness in menorrhagia and intestinal hemorrhage, as well as the powder applied topically as a hemostatic (1979, 87).

Pharmacy and dosage:. Matthew Wood mentions that the stem joints often contain water and thus the herb needs to be crushed before tincturing or drying (1992, 257).
•Fresh Plant Tincture:  crushed stems and leaf, 95% alcohol, 1:2, 3 ≠ 60 gtt
•Dry Plant Tincture: dried crushed stems and leaf, 25% alcohol, 1:5, 2-6 mL
•Decoction: dried crushed stems and leaf, 1:20, with one-half part sugar to enhance silica extraction, 30-120 mL
•Powder: 500-4000 mg

REFERENCES

Andrade Cetto A, Wiedenfeld H, Revilla MC, Sergio IA. 2000. Hypoglycemic effect of Equisetum myriochaetum aerial parts on streptozotocin diabetic rats. J Ethnopharmacol Sep;72(1-2):129-33
Bergner, Paul.  1997. The Healing Power of Minerals: Special Nutrients and Trace Elements. Rocklin, CA: Prima
Bradley, Peter R. ed. 1992. British Herbal Compendium. Bournemouth, UK: British Herbal Medicine Association.
Dole, Jeffery. 2002. Biology and Control of Field Horsetail (Equisetum arvensis L., Horsetail Family). Available from: http://ipcm.wisc.edu/uw_weeds/extension/articles/conhorsetail.htm
Felter, HW and JU Lloyd. 1893. King's American Dispensatory. Digitized version available from http://www.ibiblio.org/herbmed/eclectic/kings/main.html.
Gurbuz I, Ustun O, Yesilada E, Sezik E, Akyurek N. 2002. In vivo gastroprotective effects of five Turkish folk remedies against ethanol-induced lesions. J Ethnopharmacol Dec;83(3):241-4
Moore, Michael.  1979. Medicinal Plants of the Mountain West. Santa Fe: Museum of New Mexico Press
Newall, Carol A., Linda A. Anderson and J.D. Phillipson. 1996. Herbal Medicines: A Guide for Health-Care Professionals. London: The Pharmaceutical Press.
Perez Gutierrez RM, Laguna GY, Walkowski A. 1985. Diuretic activity of Mexican equisetum. J Ethnopharmacol Nov-Dec;14(2-3):269-72
Revilla MC, Andrade-Cetto A, Islas S, Wiedenfeld H. 2002. Hypoglycemic effect of Equisetum myriochaetum aerial parts on type 2 diabetic patients. J Ethnopharmacol Jun;81(1):117-20
Weiss, Rudolf. 1988. Herbal Medicine. Translated by A.R. Meuss. Beaconsfield, England: Beaconsfield Publishers
Willard, Terry. 1992. Textbook of Advanced Herbology. Calgary: Wild Rose College of Natural Healing.
Wood, Matthew. 1997. The Book of Herbal Wisdom. Berkeley: North Atlantic Books.
Xu CF, Bian XY, Qu SM, You LH, Qi ZM, Cheng W, Liu XJ, Liu WZ, Ren SJ.
1993. Effect of Equisetum hyemale on experimental hyperlipemia in rats and its toxic test. Zhongguo Zhong Yao Za Zhi Jan;18(1):52-3, 64