Horsetail
The horsetails are vascular plants, comprising 15 species of plants in the genus
Equisetum. This genus is the only one in the family Equisetaceae, which in turn is the only family in the order Equisetales and the class Equisetopsida. This class is often placed as the sole member of the Division Equisetophyta , though some recent molecular analyses place the genus within
Pteridophyta, related to Marattiales. The molecular data, however, are somewhat ambiguous as of yet. Other classes and orders of Equisetophyta are known from the
fossil record, where they were important members of the world
flora during the Carboniferous period.
Encyclopedia
The
horsetails are vascular plants, comprising 15 species of plants in the genus
Equisetum. This genus is the only one in the family
Equisetaceae, which in turn is the only family in the order
Equisetales and the class
Equisetopsida. This class is often placed as the sole member of the Division Equisetophyta , though some recent molecular analyses place the genus within
Pteridophyta, related to Marattiales. The molecular data, however, are somewhat ambiguous as of yet. Other classes and orders of Equisetophyta are known from the
fossil record, where they were important members of the world
flora during the Carboniferous period.
The name horsetail arose because it was thought that the stalk resembled a horse's tail, the name
Equisetum being from the
Latin equus, "horse", and
seta, "bristle". Other names, rarely used, include
candock , and
scouring-rush . The latter refers to the plants' rush-like appearance; the stems were used for scouring cooking pots in the past .
The genus is near-cosmopolitan, being absent only from
Australasia and
Antarctica. They are
perennial plants, either herbaceous, dying back in winter or
evergreen . They mostly grow 0.2-1.5 m tall, though
E. telmateia can exceptionally reach 2.5 m, and the tropical
American species
E. giganteum 5 m, and
E. myriochaetum 8 m.
In these plants the
leaves are greatly reduced, in
whorls of small, segments fused into nodal sheaths. The stems are green and
photosynthetic, also distinctive in being hollow, jointed, and ridged . There may or may not be whorls of branches at the nodes; when present, these branches are identical to the main stem except smaller.
The
spores are borne in cone-like structures at the tips of some of the stems. In many species the cone-bearing stems are unbranched, and in some they are non-photosynthetic, produced early in spring separately from photosynthetic sterile stems. In some other species they are very similar to sterile stems, photosynthetic and with whorls of branches.
Horsetails are mostly
homosporous, though in
E. arvense, smaller spores give rise to male prothalli. The
spores have four
elaters that act as moisture-sensitive springs, assisting spore dispersal after the
sporangia have split open longitudinally.
Many plants in this genus prefer wet
sandy
soils, though some are aquatic and others adapted to wet
clay soils. One horsetail,
E. arvense, can be a nuisance weed because it readily regrows after being pulled out. The stalks arise from
rhizomes that are deep underground and almost impossible to dig out. It is also unaffected by many
herbicides designed to kill
seed plants. The foliage of some species is
poisonous to grazing animals if eaten in large quantities.
The horsetails were a much larger and more diverse group in the distant past before
seed plants became dominant across the Earth. Some species were large
trees reaching to 30 m tall. The genus
Calamites is a genus of extinct [i] arborescent horsetails to which the modern horsetail [i]s are cl ...
is abundant in
coal deposits from the Carboniferous period.
Species
;Subgenus
Equisetum- Equisetum arvense - Field or Common Horsetail
- Equisetum bogotense - Andean Horsetail
- Equisetum diffusum - Himalayan Horsetail
- Equisetum fluviatile - Water Horsetail
- Equisetum palustre - Marsh Horsetail
- Equisetum pratense - Shade or Meadow Horsetail
- Equisetum sylvaticum - Wood Horsetail
- Equisetum telmateia - Great Horsetail
;Subgenus
Hippochaete- Equisetum giganteum - Giant Horsetail
- Equisetum myriochaetum - Mexican Giant Horsetail
- Equisetum hyemale - Rough Horsetail
- Equisetum laevigatum - Smooth Horsetail
- Equisetum ramosissimum - Branched Horsetail
- Equisetum scirpoides - Dwarf Horsetail
- Equisetum variegatum - Variegated Horsetail
Named hybrids
;Hybrids between species in subgenus
Equisetum- Equisetum × litorale Kühlew ex Rupr. = Equisetum fluviatile × Equisetum arvense
- Equisetum × dycei C.N.Page = Equisetum fluviatile × Equisetum palustre
- Equisetum × willmotii C.N.Page = Equisetum fluviatile × Equisetum telmateia
- Equisetum × rothmaleri C.N.Page = Equisetum arvense × Equisetum palustre
- Equisetum × robertsii Dines = Equisetum arvense × Equisetum telmateia
- Equisetum × mildeanum Rothm. = Equisetum pratense × Equisetum sylvaticum
- Equisetum × bowmanii C.N.Page = Equisetum sylvaticum × Equisetum telmateia
- Equisetum × font–queri Rothm. = Equisetum palustre × Equisetum telmateia
;Hybrids between species in subgenus
Hippochaete- Equisetum × moorei Newman = Equisetum hyemale × Equisetum ramosissimum
- Equisetum × trachydon A.Braun = Equisetum hyemale × Equisetum variegatum
- Equisetum × schaffneri Milde = Equisetum giganteum × Equisetum myriochaetum
- Equisetum × ferrissii Clute = Equisetum hyemale × Equisetum laevigatum
- Equisetum × nelsonii Schaffn. = Equisetum laevigatum × Equisetum variegatum
The superficially similar
flowering plant,
Mare's tail , unrelated to the genus
Equisetum, is occasionally misidentified and misnamed as a horsetail.
References and external links
- Pryer, K. M., Schuettpelz, E., Wolf, P. G., Schneider, H., Smith, A. R., and Cranfill, R. . Phylogeny and evolution of ferns with a focus on the early leptosporangiate divergences. American Journal of Botany 91: 1582-1598 .
- - includes a taxonomic list of all known species and hybrids
