Equisetum - Distribution, Ecology and Uses

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.

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. Members of the genus have been declared noxious weeds in Australia and in the US state of Oregon.

All the Equisetum are classed as "unwanted organisms" in New Zealand and are listed on the National Pest Plant Accord.

If eaten in large quantities, the foliage of some species is poisonous to grazing animals, including (somewhat ironically given its common name) being poisonous to horses. 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. The dish is similar to asparagus and is called tsukushi. 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. Indians of the North American Pacific Northwest eat the young shoots of this plant raw. 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.