Everything about Horsetail Family totally explained
Equisetum is a genus of
vascular plants that reproduce by spores rather than seeds. The genus includes 15 species commonly known as
horsetails and
scouring rushes. It is the only living genus in
class Equisetopsida, formerly of the division Equisetophyta (Arthrophyta in older works), though recent molecular analyses place the genus within the ferns (
Pteridophyta). Other classes and orders of Equisetopsida are known from the
fossil record, where they were important members of the world
flora during the
Carboniferous period.
Etymology
The name horsetail, often used for the entire group, arose because the branched species somewhat resemble a horse's tail, the name
Equisetum being from the
Latin equus, "horse", and
seta, "bristle". Other names include
candock (applied to branching species only), and
scouring-rush (applied to the unbranched or sparsely branched species). The latter name refers to the plants' rush-like appearance; the stems were used for scouring cooking pots in the past (due to them being coated with abrasive
silica).
Distribution
The genus is near-
cosmopolitan, being absent only from
Australasia and
Antarctica. They are
perennial plants, either
herbaceous, dying back in winter (most temperate species) or
evergreen (some tropical species, and the temperate species
Equisetum hyemale, E. scirpoides, E. variegatum and
E. ramosissimum). 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.
Equisetum is a 3ft. bamboo like substance.
Anatomy
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 these microphylls probably evolved by the reduction of a megaphyll; therefore they're commonly referred to as megaphylls to reflect this homology.
They grow in
whorls fused into nodal sheaths. The stems are green and
photosynthetic, also distinctive in being hollow, jointed, and ridged (with (3-) 6-40 ridges). There may or may not be whorls of branches at the nodes; when present, these branches are identical to the main stem except smaller.
Spores
The
spores are borne under sporangiophores in cone-like structures (
strobilus, pl.
strobili) at the tips of some of the stems. In many species the cone-bearing stems are unbranched, and in some (for example
E. arvense) they're non-photosynthetic, produced early in spring separately from photosynthetic sterile stems. In some other species (for example
E. palustre) they're 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.
Habitat
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.
Equisetum is cooked and eaten in Japan.
Geological history
The horsetails are the sole surviving genus of the
Equisetopsida, a diverse and widespread group during the
Carboniferous period. Some species were large
trees reaching to 30 m tall. The genus
Calamites (family
Calamitaceae) is abundant in
coal deposits from the Carboniferous period.
Species
Subgenus Equisetum
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 (A.A.Eat.) Schaffn. = Equisetum laevigatum × Equisetum variegatum
The superficially similar flowering plant, Mare's tail (Hippuris vulgaris), unrelated to the genus Equisetum, is occasionally misidentified and misnamed as a horsetail.
Further Information
Get more info on 'Horsetail Family'.
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