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Equisetum (/ ˌ ɛ k w ɪ ˈ s iː t əm /; 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.
The extant horsetails represent a tiny fraction of horsetail diversity in the past. There were three orders of the Equisetidae. The Pseudoborniales first appeared in the late Devonian. [1] The Sphenophyllales were a dominant member of the Carboniferous understory, and prospered until the mid and early Permian.
Equisetum arvense, the field horsetail or common horsetail, is an herbaceous perennial plant in the Equisetidae (horsetails) sub-class, native throughout the arctic and temperate regions of the Northern Hemisphere. It has separate sterile non-reproductive and fertile spore-bearing stems growing from a perennial underground rhizomatous stem system.
Equisetum palustre, the marsh horsetail, [2] is a perennial herbaceous pteridophyte belonging to the subclass of horsetails (Equisetidae). It is widespread in cooler regions of Eurasia and North America .
Equisetum hyemale (rough horsetail [2]) is an evergreen perennial herbaceous pteridophyte in the horsetail family Equisetaceae native to Eurasia and Greenland. It was formerly widely treated in a broader sense including a subspecies (subsp. affine ) in North America, but this is now treated as a separate species, Equisetum praealtum .
The green stems grow 50–150 cm tall and 2–8 mm thick. The leaf sheaths are narrow, with 15-20 black-tipped teeth. [2] Many, but not all, stems also have whorls of short ascending and spreading branches 1–5 cm long, with the longest branches on the lower middle of the stem.
Equisetum telmateia, the great horsetail, is a species of Equisetum (horsetail) native to Europe, western Asia and northwest Africa. [ 2 ] [ 3 ] It was formerly widely treated in a broader sense including a subspecies (subsp. braunii ) in western North America, but this is now treated as a separate species, Equisetum braunii .
The stems are the stoutest of any horsetail, 1–2 cm diameter (up to 3.5 cm (1.33 inches) in diameter in some populations), [5] and bear numerous whorls of very slender branches; these branches are not further branched, but some terminate in spore cones. Unlike some other horsetails, it does not have separate photosynthetic sterile and non ...