Field Horsetail (Equisetum arvense)

Family:

Horsetail Family (Equisetaceae)

Other Names:

bottle-brush, common horsetail, equisetum, horsetail, horse-pipes, joint-grass, mare's-tail, meadow-pine, paddock-pipes, pine-grass, scouringrush, shave-grass, snakegrass.

Origin and Distribution:

Field horsetail is a native species that can be found throughout the world. This species is most common in the temperate zones of North America, Europe and Russia. Field horsetail has been noted in 25 crops around the globe, predominantly in cereals and grasses, but it can also be found in vegetable crops, pastures, landscape settings, woodlands, waste areas, roadsides and along railroads. It can tolerate a range of soil conditions, but does best in sandy, gravelly or wet, poorly drained soils.

Plant Description:

Field horsetail is a primitive plant, characterized by slender, jointed stems that are of two types, fertile (reproductive) and sterile (vegetative). The pale brown fertile stems appear in early spring, each producing a pinecone-like terminal fruiting head. Green sterile stems emerge later, and are highly branched, resembling a bottle-brush. Like ferns, field horsetail does not produce flowers or seeds. This species reproduces by spores and more commonly by creeping rhizomes (horizontal underground stems) and tubers.

  • Root System:

    Dark brown to blackish, creeping rhizomes (horizontal underground stems) form an extensive system 5 feet below the ground (sometimes as deep as 20 feet). Rhizomes are forked and covered with a brown felt. Small tubers are produced along the rhizomes.

  • Stems:

    Field horsetail produces two types of stems, fertile (reproductive) and sterile (vegetative). Both stem types are slender, hollow, jointed, vertically ridged and round in cross-section. FERTILE STEMS are whitish to pale brown, unbranched and somewhat succulent, with large, easily separated joints (nodes) and a terminal pinecone-like, spore-producing head (1 to 4 inches long). Fertile stems can grow 4 to 10 inches tall (sometimes up to 12 inches). STERILE STEMS are green, rough, wiry, and either erect or sagging at the base. Sterile stems can grow 4 to 20 inches tall (sometimes up to 25 inches). Whorls of 4-angled, green, needle-like, leafless branches (4 to 6 inches long) occur at the middle and upper joints. The branches may be horizontal or point upward. Sterile stems and branches are covered with rough silica deposits. The distance between joints is shorter for sterile stems than for fertile stems.

  • Leaves:

    Reduced, scale-like leaves are fused to form a tube-like, toothed sheath surrounding each joint of fertile and sterile stems (8 to 12 leaves per sheath). The upper edge of the sheath is black. Sheaths are more prominent on fertile stems. On sterile stems, the sheaths are located above the branch whorls.

  • Fruits and Seeds:

    The pinecone-like structure formed at the end of the fertile stem produces thousands of minute, pale green to yellowish spores.

Similar Species:

Field horsetail may be confused with a related species, scouringrush (Equisetum hyemale). However, both the fertile and sterile stems of scouringrush are green and lack the whorls of branches characteristic of field horsetail.

Biology:

Fertile stems emerge in mid-April, begin spore production in early May, and die soon after. Sterile stems emerge in late spring as the fertile stems wither, and persist until frost.

Rhizomes of field horsetail have been found to grow as much as 330 feet horizontally and 20 feet deep. New shoots can emerge from depths of 3 feet or more. The small tubers produced along the rhizomes are capable of surviving long periods in the soil. New plants can arise from both rhizome fragments and tubers. Field horsetail has the ability to selectively accumulate heavy metals from the soil in its tissues at a higher concentration than in the soil. The green sterile stems and branches are rich in chlorophyll, and take the place of leaves in conducting photosynthesis. The pale fertile stems lack chlorophyll.

Field horsetail is resistant to most agronomic herbicides, and can survive under many conditions because of its deep rhizomes and tubers. Rhizome fragments and tubers are easily spread to new areas in infested soil. As a result, this species is often difficult to control. It can be a strong competitor with crops, as well as a threat to grazing animals due to toxic compounds. In addition, field horsetail extracts can inhibit germination and reduce vigor of 30 grass species.

Toxicity:

Field horsetail is reported as very toxic to livestock. Animals poisoned by this plant are said to have "equisetosis", a phenomenon documented on several continents and throughout the world. In monogastric animals such as horses, consumption of field horsetail can cause vitamin B1 deficiency. This species also contains high levels of toxic alkaloids. Sheep and cattle are more likely to be poisoned by fresh plants, while horses are more susceptible to poisoning from contaminated hay. General symptoms of poisoning include weakness, lack of coordination, and difficulty breathing.

Facts and Folklore:

  • The genus name, Equisetum, translates to "horse-bristle" or tail, describing the appearance of the sterile stems.

  • Deposits of silica cover the vegetative stems and branches of field horsetail. For this reason, the plant has been used to scour pots, pans, and articles containing silver (hence the common name 'scouringrush').

  • Field horsetail may accumulate more gold than any other plant. Up to 4 1/2 ounces of gold per ton of fresh plant material has been recovered. Mining engineers consider field horsetail an indicator species of gold, but not a viable commercial source.

  • Tubers of field horsetail are rich in starch and are eaten by wildlife. Native Americans consumed young fertile shoots.

  • Field horsetail has been used medicinally as a diuretic and to control hemorrhaging.