Equisetum is a "living fossil", the only living genus of the entire class Equisetopsida, which for over 100 million years was much more diverse and dominated the understory of late Paleozoic forests. Some Equisetopsida were large trees reaching to 30 meters tall. The genus Calamites of the family Calamitaceae, for example, is abundant in coal deposits from the Carboniferous period. The pattern of spacing of nodes in horsetails, wherein those toward the apex of the shoot are increasingly close together, inspired John Napier to invent logarithms.
A superficially similar but entirely unrelated flowering plant genus, mare's tail (Hippuris), is occasionally referred to as "horsetail", and adding to confusion, the name mare's tail is sometimes applied to Equisetum.
|"Candocks" of the great horsetail (Equisetum telmateia subsp. telmateia), showing whorls of branches and the tiny dark-tipped leaves|
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 is derived from the Latin equus ("horse") + seta ("bristle").
Other names include candock for branching individuals, and snake grass or scouring-rush for unbranched or sparsely branched individuals. The latter name refers to the rush-like appearance of the plants 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. In Spanish-speaking countries, these plants are known as cola de caballo, meaning "horsetail".
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 ancestral as in Lycopodiophyta (clubmosses and relatives), but rather derived adaptations, evolved by reduction of megaphylls. They are, therefore, sometimes referred to as megaphylls to reflect this homology.
The leaves of horsetails are arranged in whorls fused into nodal sheaths. The stems are usually green and photosynthetic, and are distinctive in being hollow, jointed and ridged (with sometimes 3 but usually 6–40 ridges). There may or may not be whorls of branches at the nodes.
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 shoots are unbranched, and in some (e.g. field horsetail, E. arvense) they are non-photosynthetic, produced early in spring. In some other species (e.g. marsh horsetail, E. palustre) they are very similar to sterile shoots, 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 through crawling and hopping motions after the sporangia have split open longitudinally.
The crude cell extracts of all Equisetum species tested contain mixed-linkage glucan : Xyloglucan endotransglucosylase (MXE) activity. 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. 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. Non-Equisetum land plants tested lack detectable MXE activity. An observed negative correlation between XET activity and cell age led to the suggestion that XET may be catalysing endotransglycosylation in controlled wall-loosening during cell expansion. 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.
The living members of the genus Equisetum are divided into three distinct lineages, which are usually treated as subgenera. The name of the type subgenus, Equisetum, means "horse hair" in Latin, while the name of the other large subgenus, Hippochaete, means "horse hair" in Greek. Hybrids are common, but hybridization has only been recorded between members of the same subgenus. While plants of subgenus Equisetum are usually referred to as horsetails, those of subgenus Hippochaete are often called scouring rushes, especially when unbranched.
Two Equisetum plants are sold commercially under the names Equisetum japonicum (barred horsetail) and Equisetum camtschatcense (Kamchatka horsetail). These are both types of E. hyemale var. hyemale, although they may also be listed as varieties of E. hyemale.
Phylogeny of extant species (excluding hybrids), according to Christenhusz et al. (2019)
The genus Equisetum as a whole, while concentrated in the non-tropical northern hemisphere, is near-cosmopolitan, being absent only from Antarctica, though they are not known to be native to Australia, New Zealand nor the islands of the Pacific. They are most common in northern North America (Canada and the northernmost United States), where the genus is represented by nine species (arvense, fluviatile, palustre, pratense, sylvaticum, hyemale, laevigatum, scirpoides, and variegatum). Only four (bogotense, giganteum, myriochaetum, and ramosissimum) of the fifteen species are known to be native south of the Equator. They are perennial plants, 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 typically 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.
One species, Equisetum fluviatile, is an emergent aquatic, rooted in water with shoots growing into the air. The stalks arise from rhizomes that are deep underground and difficult to dig out. The field horsetail (E. arvense) can be a nuisance weed, readily regrowing from the rhizome after being pulled out. It is unaffected by many herbicides designed to kill seed plants. Since the leaves have a waxy coat, the plant is resistant to contact weedkillers like glyphosate. 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.
People have regularly consumed horsetails. For example, the fertile stems bearing strobili of some species are cooked and eaten like asparagus (a dish called tsukushi) in Japan. Native Americans in the Pacific Northwest eat the young shoots of this plant raw. The young plants are eaten cooked or raw, but considerable care must be taken.
If eaten over a long enough period of time, some species of horsetail can be poisonous to grazing animals, including horses. The toxicity appears to be due to thiaminase, which can cause thiamin (vitamin B1) deficiency.
Extracts and other preparations of E. arvense have served as herbal remedies, with records dating over centuries. In 2009, the European Food Safety Authority concluded there was no evidence for the supposed health effects of E. arvense, such as for invigoration, weight control, skincare, hair health or bone health. As of 2018, there is insufficient scientific evidence for its effectiveness as a medicine to treat any human condition.
E. arvense contains thiaminase, which metabolizes the B vitamin, thiamine, potentially causing thiamine deficiency and associated liver damage, if taken chronically. Horsetail might produce a diuretic effect. Further, its safety for oral consumption has not been sufficiently evaluated and it may be toxic, especially to children and pregnant women.
Equisetaceae, sometimes called the horsetail family, is the only extant family of the order Equisetales, with one surviving genus, Equisetum, which comprises about twenty species.Equisetales
Equisetales is an order of subclass Equisetidae with only one living family, Equisetaceae, containing the genus Equisetum (horsetails).Equisetopsida
Equisetopsida, or Sphenopsida, is a class of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. Living horsetails are represented by about twenty herbaceous species in the single genus Equisetum. They typically grow in wet areas, with whorls of needle-like branches radiating at regular intervals from a single vertical stem.
The Equisetopsida were formerly regarded as a separate division of spore plants and also called Equisetophyta, Arthrophyta, Calamophyta or Sphenophyta; today they have been recognized as rather close relatives of the typical ferns (Pteridopsida) and form a specialized lineage of the Pteridophyta. However, the division between the Equisetopsids and the ferns is so ancient that many botanists, especially paleobotanists, still regard this group as fundamentally separate at the higher level.Equisetum arvense
Equisetum arvense, the field horsetail or common horsetail, is an herbaceous perennial plant in the Equisetopsida (the horsetails), native throughout the arctic and temperate regions of the northern hemisphere. It has separate sterile non-reproductive and fertile spore-bearing stems growing from a perennial underground rhizomatous stem system. The fertile stems are produced in early spring and are non-photosynthetic, while the green sterile stems start to grow after the fertile stems have wilted and persist through the summer until the first autumn frosts. It is sometimes confused with mare's tail, Hippuris vulgaris.Equisetum fluviatile
Equisetum fluviatile, the water horsetail or swamp horsetail, is a vascular plant that commonly grows in dense colonies along freshwater shorelines or in shallow water in ponds, swamps, ditches, and other sluggish or still waters with mud bottoms. It is a perennial herbaceous species, growing 30–100 cm (rarely 140 cm) tall with erect dark green stems 2–8 mm in diameter, smooth, with about 10–30 fine ridges. At each joint, the stem has a whorl of tiny, black-tipped scale leaves 5–10 mm long. Many, but not all, stems also have whorls of short ascending and spreading branches 1–5 cm long, with the longest branches on the lower middle of the stem. The side branches are slender, dark green, and have 1–8 nodes with a whorl of five scale leaves at each node. The water horsetail has the largest central hollow of the horsetails, with 80% of the stem diameter typically being hollow.
The stems readily pull apart at the joints, and both fertile and sterile stems look alike.
The water horsetail reproduces both by spores and vegetatively by rhizomes. It primarily reproduces by vegetative means, with the majority of shoots arising from rhizomes. Spores are produced in blunt-tipped cones at the tips of some stems. The spore cones are yellowish-green, 1–2 cm long and 1 cm broad, with numerous scales in dense whorls.
The water horsetail ranges throughout the temperate Northern Hemisphere, from Eurasia south to central Spain, Italy, the Caucasus, China, Korea and Japan, and in North America from the Aleutian Islands to Newfoundland, south to Oregon, Idaho, northwest Montana, northeast Wyoming, West Virginia and Virginia.
This horsetail is sometimes seen as an invasive species because it is very hardy and tends to overwhelm other garden plants unless it is contained. When planting, it is best to plant them with the rhizome in a container.
The water horsetail is most often confused with the marsh horsetail E. palustre, which has rougher stems with fewer (4-8) stem ridges with a smaller hollow in the stem centre, and longer spore cones 2–4 cm long.Equisetum giganteum
Equisetum giganteum, with the common name southern giant horsetail, is a species of horsetail native to South America and Central America, from central Chile east to Brazil and north to southern Mexico.Equisetum hyemale
Equisetum hyemale (commonly known as rough horsetail, scouring rush, scouringrush horsetail and, in South Africa, as snake grass) is a perennial herb in the fern Phylum Pteridophyta. It is a native plant throughout the Holarctic Kingdom, found in North America, Europe, and northern Asia.Equisetum laevigatum
Equisetum laevigatum is a species of horsetail known by the common names smooth horsetail and smooth scouring rush. This plant is native to much of North America except for northern Canada and southern Mexico. It is usually found in moist areas in sandy and gravelly substrates. It may be annual or perennial. It grows narrow green stems sometimes reaching heights exceeding 1.5 meters. The leaves at the nodes are small, scale-like brownish sheaths and there are occasionally small, spindly branches. The stems are topped with rounded cone-shaped sporangia.Equisetum myriochaetum
Equisetum myriochaetum, also known as Mexican giant horsetail, is a species of horsetail that is native to Nicaragua, Costa Rica, Colombia, Venezuela, Ecuador, Peru and Mexico.
It is the largest horsetail species, commonly reaching 15 feet (4.6 m), with the largest recorded specimen having a height of 24 feet (7.3 m).Equisetum palustre
Equisetum palustre, the marsh horsetail, is a plant species belonging to the division of horsetails (Equisetopsida). It is widespread in cooler regions of North America and Eurasia.Equisetum pratense
Equisetum pratense, commonly known as meadow horsetail, shade horsetail or shady horsetail, is a widespread horsetail (Equisetophyta) fern. Shade horsetail can be commonly found in forests with tall trees or very thick foliage that can provide shade and tends to grow closer and thicker around streams, ponds and rivers. The specific epithet pratense is Latin, meaning pasture or meadow dwelling.Equisetum ramosissimum
Equisetum ramosissimum Desf., known as branched horsetail, is a species of evergreen horsetail (genus Equisetum, subgenus Hippochaete). It is not the same species as Equisetum ramosissimum Kunth, which is a synonym of Equisetum giganteum.Botanists today recognize two subspecies. The type subspecies, E. ramosissimum subsp. ramosissimum, is native through much of Asia, Europe, and Africa, with an introduced population in the southeast United States. E. ramosissimum subsp.debile, sometimes treated as the separate species E. debile, is found in southeast Asia and some Pacific islands. The type subspecies has more obvious branching from the aerial stem than subspecies debile.Equisetum scirpoides
Equisetum scirpoides (dwarf scouring rush or dwarf horsetail) Michx., Fl. Bor.-Amer. 2: 281 (1803). 2 n = 216. The smallest of the currently occurring representatives of the genus Equisetum (horsetail).
It occurs mainly in the area of the Arctic Circle in Alaska for the Indians and Greenland, Idaho, Montana, South Dakota, Minnesota, Iowa, Illinois, New York and New England. Creates a compact and dense clumps. Reaches a maximum height of about 30 cm. The assimilation and generative shoots are identical and grow together. The leaves reduced to a black sheath around the stem. The stems are green, unbranched, thick and about 1 mm with six ribs. The generative shoots with small cones dying after sowing the spores. The nodes occur at approximately 1 – 3 cm. The leaves are very small to about 1 mm, and arranged in around nodes. The corms are thin, yellow and brown. The roots very fine, black and densely surpassing the ground. Species grows best in the mud at the depth zone from 0 to 3 cm. Specimens reproduce primarily by vegetative division. Equisetum scirpoides is hardy and semi-evergreen. This species is quite a popular decorative plant seen in garden ponds, ornamental gardens and assumptions in nearly the whole world. E. scirpoides was discovered and described by French botanist André Michaux. Detailed studies were conducted by the American botanist Oliver Atkins Farwell.Equisetum sylvaticum
Equisetum sylvaticum, the wood horsetail, is a horsetail (family Equisetaceae) native to the Northern Hemisphere, occurring in North America and Eurasia. Because of its lacy appearance, it is considered among the most attractive of the horsetails.Equisetum telmateia
Equisetum telmateia, the great horsetail or northern giant horsetail, is a species of Equisetum (puzzlegrass) with an unusual distribution, with one subspecies native to Europe, western Asia and northwest Africa, and a second subspecies native to western North America. The North American subspecies is often simply but ambiguously called "giant horsetail", but that name may just as well refer to the Latin American Equisetum giganteum and Equisetum myriochaetum.
There are two subspecies:
Equisetum telmateia subsp. telmateia. Great horsetail. Europe, western Asia, northwest Africa. Main stem between branch whorls pale greenish white.
Equisetum telmateia subsp. braunii (Milde) Hauke. Northern giant horsetail. Western North America, from southeastern Alaska and western British Columbia south to California. Main stem between branch whorls green.Equisetum thermale
Equisetum thermale is an extinct horsetail species in the family Equisetaceae described from a group of whole plant fossils including rhizomes, stems, and leaves. The species is known from Middle to Late Jurassic sediments exposed in the province of Santa Cruz, Argentina. It is one of several extinct species placed in the living genus Equisetum.Equisetum variegatum
Equisetum variegatum, commonly known as variegated horsetail or variegated scouring rush, is a horsetail native to the Northern Hemisphere.Gnorimoschema herbichii
Gnorimoschema herbichii is a moth in the family Gelechiidae. It was described by Nowicki in 1864. It is found in Portugal, Spain, France, the Netherlands, Germany, Denmark, Poland, Hungary, Romania, the Republic of Macedonia, the Baltic region, Norway, Finland, Ukraine and Russia. In the east, the range extends to Transbaikalia, Mongolia and Kamchatka. It is also found in North America, where it has been recorded from Alberta, Yukon, Manitoba and Ontario.The wingspan is 14–15 mm.The larvae feed on Equisetum arvense, Equisetum palustre, Suaeda maritima and Atriplex species.Strobilus
A strobilus (plural: strobili) is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but many botanists restrict the use of the term cone to the woody seed strobili of conifers. Strobili are characterized by a central axis (anatomically a stem) surrounded by spirally arranged or decussate structures that may be modified leaves or modified stems.
Leaves that bear sporangia are called sporophylls, while sporangia-bearing stems are called sporangiophores.