Thehorsetails are aclass in thePteridophyta (ferns). They were one of the most important plant groups in thePalaeozoicera.
For over 100 million years they were varied, and dominated the understorey of late Paleozoic forests. They are seen in thecoal measures of theCarboniferous period, and some were trees reaching up 30 metres.[1] The group is now almostextinct, but onegenus survives. They arevascular plants that reproduce byspores and not byseeds. The namehorsetail came because the branched species somewhat look like a horse's tail.
Modern horsetails first appeared during theJurassic period.Equisetum is the only living genus of horsetails. The nameEquisetum comes from theLatin (equus = horse; andseta = bristle).[2] The genus includes 15species.
Horsetails arenative on all continents exceptAustralasia andAntarctica. They areperennial plants. They are eitherherbaceous (they die back in winter like most temperate species) or they areevergreen (some tropical species, and some temperate species). They mostly grow 0.2-1.5 m tall, thoughE. telmateia can reach 2.5 m, and the tropicalAmerican speciesE. giganteum 5 m, andE. myriochaetum 8 m.
Strobilus ofEquisetum on an unbranched stemHow they usually look.
In these plants theleaves are very small, inwhorls joined together to make sheaths around thestem. The stems are green andphotosynthetic, also distinctive in being hollow, jointed and ridged, usually with 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.
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.E. arvense, field horsetail) they are non-photosynthetic, produced early in Springtime.
↑Pryer K.M.et al 2004. Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences.American Journal of Botany91: 1582-1598 (availableonlineArchived 2007-09-26 at theWayback Machine; pdf file)
↑Other names includecandock (applied to branching species only), andscouring-rush (applied to the unbranched or sparsely branched species). The latter name refers to the plants'rush-like appearance; the stems are coated with abrasivesilica, which made them useful for cleaning ("scouring") cooking pots in the past.
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