EQUISETACEAE

The Equisetaceae or horsetail family are Fern Allies and are a very ancient and primitive form of plant life.

Equisetum arvense

Horsetail

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Family Equisetaceae

Description

A creeping perennial with hairy rhizomes and both sterile and fertile hollow, jointed stems, longitudinally grooved and impregnated with silica. Fertile stems brown, appearing first, shorter than sterile stems, unbranched, which die after spore dispersal. Their 4–6 sheaths are also brown with dark brown teeth. Cones 10–40 mm long. Sterile stems green, 10–80 cm × 1–5 mm, branched, erect or decumbent, rough, with 6–19-toothed green sheaths. Branches are numerous, spreading, and arranged in whorls. Dies back in winter.

Equisetum hymale

Horsetail

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Family Equisetaceae

Description

Evergreen, creeping, slender, rhizomatous perennial similar to E. arvense but sterile stems green, taller, 30–100 cm with very few branches and those growing upright from the nodes rather than spreading. Stems hollow, jointed, each joint with a broad white band with a narrower black band top and bottom and 10–30 narrow blunt teeth; furrowed, with 14–40 ridges. Fertile stems also green, topped with a shorter, rounder cone. Does not die back in winter. E. hymale is the species used in Traditional Chinese Medicine.

Habitat and cultivation

Equisetums are cosmopolitan weeds in damp, wet areas of temperate regions of the Northern Hemisphere. They are considered noxious because they spread and their high silica content destroys the teeth of stock that eat them. Grown from spores or root division. Frost resistant and drought tender.

Parts used

The sterile stems of the herb harvested mid to late summer.

Active constituents1,2

1) Flavonoids3–5 (up to 1%) including apigenin, kaempferol, luteolin and quercetin glycosides. There are two chemotypes of this herb, one found in Asia and North America and the other in Europe, they vary in their specific flavonoids4

2) Phytosterols including β-sitosterol (around 60%), campesterol (around 33%), isofucosterol (around 6%) and trace amounts of cholesterol6

3) Silica in various forms including as elemental silica,7 silicic acid8 (5–8%) a small proportion of which is in a soluble form (E. hymale is richer in silica. The horsetail family is known to have the highest concentration of silica in the plant world7)

4) Volatile oil including hexahydrofarnesyl acetone, cis-geranyl acetone, thymol and transphytol9

5) Phenolics including pterosins (onitin and its glucoside)10 and caffeic acid derivatives11–13

6) Saponins—equisetonin

7) Alkaloids at very low levels, including nicotine, palustrine and palustrinine14

Also contains tannins, a bitter, aconitic acid and lectins.15

Nutritional constituents

Vitamins: Pantothenic acid, C and E16 Minerals: Silica, selenium, copper, zinc, manganese, magnesium, sodium, iron, iodine, potassium and calcium

Actions

1) Astringent especially for genitourinary tract

2) Antihaemorrhagic

3) Diuretic

4) Antilithic Locally

5) Styptic

6) Vulnerary

Scientific information

This herb has been used medicinally since ancient Greek and Roman times but was also used in traditional medicine in Asia and North America. It was listed as an official preparation in a number of European pharmacopoeias until fairly recently as a mild diuretic.17 German Commission E has approved the herb for internal use to treat bacterial infections and inflammation of the lower urinary tract and renal gravel and externally to aid poor healing wounds. Its diuretic effect is considered to be due to saponins and flavonoids. The Chinese have used it for conjunctivitis and dysentery and the Germans for bleeding in the gastrointestinal tract.

In vitro—In contrast to earlier reports18,19 the whole extract has very good anti-oxidant activity comparable with ascorbic acid, and likely due to the high vitamin C and E, copper and zinc levels.16

Equisetum inhibits platelet aggregation, an action that may be attributable to the phenolic fraction20 and also, according to the BHP, causes a mild increase in leucocytosis.

The volatile oil has very good antimicrobial activity against a number of organisms including Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeroginosa, Salmonella enteritidis, Aspergillus niger and Candida albicans.9

Onitin and luteolin are protective of hepatic cells10—the herb is used in the East for treating hepatitis.

In vivo—Equisetum in a topical combination with fatty acids and Hypericum perforatum was effective in treating and preventing pressure ulcers,21 this supports the traditional use of the herb as a vulnerary.

Although animal testing has confirmed some of the traditional uses of horsetail, there are very few human based studies and the long tradition of medicinal use is the best guide to its applications.

Medicinal uses

Respiratory tract

To heal and strengthen lung tissue has been applied to:

Urinary tract

The astringency may help to improve bladder tone and reduce prostate enlargement. Silica aids tissue healing.

BHP specific for prostatitis, prostate enlargement, incontinence and enuresis in children.

Externally

The herb is considered an aid to strengthening connective tissue due to its silica content. Used for:

Can be used as a wash for nose, eyes, mouth and vagina.

Pharmacy

Three times daily  
Infusion of dried herb –   1–4 g
Fluid extract (25%) –   1–4 ml

For infusion/decoction pour 150 ml boiling water over 2–4 g Equisetum in a pan. Boil for 5 minutes and infuse for 10–15 minutes. (According to German Commission E monograph 34% of its flavonoids are available after 5 minutes of infusion and 40% after 10 minutes.)

Pharmacokinetics

In vivo—Studies have been conducted into the metabolism of the flavonoid quercetin from a standardised extract of horsetail. It is predominantly metabolised to benzoic acid derivatives and excreted in urine as hippuric acid.22

Precautions and/or safety

The herb is apparently toxic to cattle in large quantities but is not known to cause a problem in normal therapeutic doses in humans.

There is a reported case involving the use of herbal mixtures to aid smoking cessation consisting of both tablets and liquids (only the latter contained Equisetum) which resulted in transient but complete atrioventricular block in an otherwise healthy man.23 Seborrhoeic dermatitis attributed to the nicotine in horsetails has also been reported.24

Historical uses

To ease bowels; for “coughs that come, by distillation, from the head” (Culpeper); chilblains, rheumatic, arthritic and skin problems; dropsy; a strong infusion as an emmenagogue.