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Equisetum
| Equisetum Temporal range:
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|---|---|
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| Vegetative stems of Equisetum telmateia (great horsetail), showing whorls of branches and the tiny dark-tipped leaves | |
Scientific classification 
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| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Division: | Polypodiophyta |
| Class: | Polypodiopsida |
| Subclass: | Equisetidae |
| Order: | Equisetales |
| Family: | Equisetaceae |
| Genus: | Equisetum L. |
| Type species | |
| Equisetum arvense | |
| Species | |
|
See text | |
| Synonyms[1] | |
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Equisetum (/ˌɛkwɪˈsiːtəm/; horsetail) is the only living genus in Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.[2]
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 trees reaching to 30 m (98 ft) tall.[3] 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, is said to have inspired John Napier to invent logarithms.[4] Modern horsetails first appeared during the Jurassic period.
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.[5]
- ^ "Equisetum L." Plants of the World Online. Board of Trustees of the Royal Botanic Gardens, Kew. 2024. Retrieved 15 September 2024.
- ^ Dunmire, John R.; Williamson, Joseph F. (1995). "EQUISETUM hyemale". In Brenzel, Kathleen N. (ed.). Western Garden Book. Menlo Park, CA: Sunset. pp. 274, 606. ISBN 0376038500.
- ^ "An Introduction to the Genus Equisetum and the Class Sphenopsida as a whole". Florida International University. Archived from the original on 2009-07-14. Retrieved 2009-07-22.
- ^ Sacks, Oliver (25 July 2011). "Hunting Horsetails". The Talk of the Town: Field Trip. The New Yorker. No. 11 August 2011.
- ^ "Equisetum". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
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