Equisetum (; horsetail) is the only living genus in Equisetaceae, a family of that reproduce by rather than seeds.
Equisetum is a "living fossil", the only living genus of the entire subclass Equisetidae, which for over 100 million years was much more diverse and dominated the understorey of late Paleozoic forests. Some equisetids were large reaching to tall.
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.
Etymology
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 species, marestail, puzzlegrass, and snake grass or scouring-rush for unbranched or sparsely branched species. The latter name refers to the Juncus-like appearance of the plants and to the fact that the stems are coated with abrasive , making them useful for scouring (cleaning) metal items such as cooking pots or drinking mugs, particularly those made of tin. Equisetum hyemale, rough horsetail, is still boiled and then dried in Japan to be used for the final polishing process on Woodworking to produce a smooth finish.
Description
Equisetum Leaf are greatly reduced and usually non-
Photosynthesis. They contain a single, non-branching
vascular bundle, which is the defining feature of
. However, it has recently been recognised that horsetail microphylls are probably not ancestral as in
(clubmosses and relatives), but rather derived
, evolved by reduction of .
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.[Streeter D, Hart-Davies C, Hardcastle A, Cole F, Harper L. 2009. Collins Flower Guide. Harper Collins ] Unusually, the branches often emerge below the leaves in an internode, and grow from buds between their bases.
Spores
The
are borne under
in
strobilus, 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.
E. arvense, field horsetail) they are non-photosynthetic, produced early in spring. In some other species (e.g.
E. palustre, marsh horsetail) they are very similar to sterile shoots, photosynthetic and with whorls of branches.
Horsetails are mostly Spore, though in the field horsetail, smaller spores give rise to male Prothallus. The spores have four that act as moisture-sensitive springs, assisting spore dispersal through crawling and hopping motions after the Sporangium have split open longitudinally.
Cell walls
The crude cell extracts of all
Equisetum species tested contain (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 is 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.
Taxonomy
Species
Currently, 18 species of
Equisetum are accepted by Plants of the World Online.
[ The living members are divided into three distinct lineages, which are usually treated as Subgenus. 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 Ancient Greek. Hybrids are common, but hybridization has only been recorded between members of the same subgenus.]
Two Equisetum plants are sold 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 separate varieties of E. hyemale.
Evolutionary history
The oldest remains of modern horsetails of the genus Equisetum first appear in the Early Jurassic, represented by Equisetum dimorphum from the Early Jurassic of Patagonia[Gould, R. E. 1968. Morphology of Equisetum laterale Phillips, 1829, and E. bryanii sp. nov. from the Mesozoic of south‐eastern Queensland. Australian Journal of Botany 16: 153–176.]
Subgenus Paramochaete
-
– Andean horsetail; upland South America up to Costa Rica; includes E. rinihuense, sometimes treated as a separate species. Previously included in subg. Equisetum, but Christenhusz et al. (2019)
Subgenus Equisetum
-
– field horsetail or common horsetail; circumboreal down through temperate zones
-
– northern giant horsetail, syn. E. telmateia subsp. braunii (Milde) Hauke.; west coast of North America
-
– Himalayan horsetail; Himalayan India and China and adjacent nations above about
-
– water horsetail; circumboreal down through temperate zones
-
– marsh horsetail; circumboreal down through temperate zones
-
– shady horsetail, meadow horsetail, shade horsetail; circumboreal except for tundra down through cool temperate zones
-
– wood horsetail; circumboreal down through cool temperate zones, more restricted in east Asia
-
– great horsetail; Europe to Asia Minor and north Africa. The former North American subspecies Equisetum telmateia subsp. braunii (Milde) Hauke is now treated as a separate species
[
]
Subgenus Hippochaete
-
– southern giant horsetail or giant horsetail; temperate to tropical South America and Central America north to southern Mexico
-
– rough horsetail; most of non-tropical Old World. The former North American subspecies Equisetum hyemale subsp. affine (Engelm.) A.A.Eat. is now treated as a separate species
[
]
-
– smooth horsetail, smooth scouringrush; western 3/4 of North America down into northwestern Mexico; also sometimes known as Equisetum kansanum
-
– Mexican giant horsetail; from central Mexico south to Peru
-
– scouringrush horsetail, syn. E. hyemale subsp. affine (Engelm.) A.A.Eat.; temperate North America
-
(including Equisetum debile) – branched horsetail; Asia, Europe, Africa, southwest Pacific islands
-
– dwarf horsetail, dwarf scouringrush; northern (cool temperate) zones worldwide
-
– variegated horsetail, variegated scouringrush; northern (cool temperate) zones worldwide, except for northeasternmost Asia
-
– Atacama Desert giant horsetail; southern Peru, northern Chile
Unplaced to subgenus
Named hybrids
Hybrids between species in subgenus Equisetum
-
Equisetum × bowmanii ( Equisetum sylvaticum × Equisetum telmateia)
-
Equisetum × dycei ( Equisetum fluviatile × Equisetum palustre)
-
Equisetum × font-queri ( Equisetum palustre × Equisetum telmateia)
-
Equisetum × litorale ( Equisetum arvense × Equisetum fluviatile)
-
Equisetum × mchaffieae ( Equisetum fluviatile × Equisetum pratense)
-
Equisetum × mildeanum ( Equisetum pratense × Equisetum sylvaticum)
-
Equisetum × robertsii ( Equisetum arvense × Equisetum telmateia)
-
Equisetum × rothmaleri ( Equisetum arvense × Equisetum palustre)
-
Equisetum × willmotii ( Equisetum fluviatile × Equisetum telmateia)
Hybrids between species in subgenus Hippochaete
-
Equisetum × ferrissii ( Equisetum hyemale × Equisetum laevigatum)
-
Equisetum × moorei ( Equisetum hyemale × Equisetum ramosissimum)
-
Equisetum × nelsonii ( Equisetum laevigatum × Equisetum variegatum)
-
Equisetum × schaffneri ( Equisetum giganteum × Equisetum myriochaetum)
-
Equisetum × trachyodon ( Equisetum hyemale × Equisetum variegatum)
Phylogeny
Distribution and ecology
The genus Equisetum as a whole, while concentrated in the non-tropical northern hemisphere, is near-cosmopolitan, being absent naturally only from Antarctica, Australia, New Zealand, and the islands of the Pacific Ocean. They are most common in northern Europe, with ten species ( E. arvense, E. fluviatile, E. hyemale, E. palustre, E. pratense, E. ramosissimum, E. scirpoides, E. sylvaticum, E. telmateia, and E. variegatum); Great Britain has nine of these species, missing only E. scirpoides of the European list.[ Northern North America (Canada and the northernmost United States), also has nine species ( E. arvense, E. fluviatile, E. laevigatum, E. palustre, E. praealtum, E. pratense, E. scirpoides, E. sylvaticum, and E. variegatum). Only five ( E. bogotense, E. giganteum, E. myriochaetum, E. ramosissimum, and E. xylochaetum) of the eighteen species are known to be native south of the Equator.
]
They are , Herbaceous plant and dying back in winter in most temperate species, or evergreen as most tropical species and the temperate species E. hyemale (rough horsetail), E. ramosissimum (branched horsetail), E. scirpoides (dwarf horsetail) and E. variegatum (variegated horsetail). They typically grow 20 cm–1.5 m (8 in–5 ft) tall, though the subtropical "giant horsetails" are recorded to grow as high as ( E. giganteum, southern giant horsetail) or ( E. myriochaetum, Mexican giant horsetail), and allegedly even more.
One species, Equisetum fluviatile, is an emergent Aquatic plant, rooted in water with shoots growing into the air. The stalks arise from that are deep underground and difficult to dig out. Field horsetail ( E. arvense) can be a nuisance weed, readily regrowing from the rhizome after being pulled out. It is unaffected by many designed to kill Spermatophyte.
All the Equisetum are classed as "unwanted organisms" in New Zealand and are listed on the National Pest Plant Accord.
Consumption
People have regularly consumed horsetails. The fertile stems bearing strobili of some species can be cooked and eaten like asparagus[
]
If eaten over a long enough period of time, some species of horsetail can be to grazing animals, including horses.
Equisetum species may have been a common food for herbivorous dinosaurs. With studies showing that horsetails are nutritionally of high quality, it is assumed that horsetails were an important component of herbivorous dinosaur diets.
Folk medicine and safety concerns
Extracts and other preparations of E. arvense have served as herbal remedies, with records dating over centuries.[
]
E. arvense contains thiaminase, which metabolizes the B vitamins, thiamine, potentially causing thiamine deficiency and associated hepatotoxicity, if taken chronically.[ Horsetail might produce a diuresis.][ Further, its safety for oral consumption has not been sufficiently evaluated and it may be toxicity, especially to children and pregnant women.][
]
See also
-
List of plants poisonous to equines
Further reading
External links
