Equisetaceae, also known as the horsetail family, is a family of

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

s and the only

surviving Survival skills are techniques used to sustain life in any type of natural environment or built environment. These techniques are meant to provide basic necessities for human life, including water, food, and shelter. Survival skills also sup ...

family of the order Equisetales, with one surviving genus, ''

Equisetum ''Equisetum'' (; horsetail) is the only living genus in Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds. ''Equisetum'' is a "living fossil", the only living genus of the entire subclass Equisetidae, which ...

'', comprising about twenty species.

Evolution and systematics

Equisetaceae is the only surviving family of the Equisetales, a group with many fossils of large tree-like plants that possessed ribbed stems similar to modern horsetails. '' Pseudobornia'' is the oldest known relative of ''Equisetum''; it grew in the late

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

, about 375

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

and is assigned to its own order. All living horsetails are placed in the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

''. But there are some

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

that are not assignable to the modern genus. '' Equisetites'' is a " wastebin taxon" uniting all sorts of large horsetails from the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

; it is almost certainly

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

and would probably warrant being subsumed in ''Equisetum''. But while some of the species placed there are likely to be ancestral to the modern horsetails, there have been reports of

secondary growth In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips ...

in other ''Equisetites'', and these probably represent a distinct and now-extinct horsetail lineage. '' Equicalastrobus'' is the name given to fossil horsetail strobili, which probably mostly or completely belong to the (sterile) plants placed in ''Equisetites''. The earliest fossils that can be reliably attributed to the Equisetaceae proper date to the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

References

External links

UCMP – Equisetaceae
{{Authority control Fern families Mesozoic first appearances