Equisetaceae
Encyclopedia
Equisetaceae, sometimes called the horsetail family, is the only extant family of the class Equisetales
, with one surviving genus, Equisetum, which comprises about twenty species.
, 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
, about 375 million years ago and is assigned to its own order.
All living horsetails are placed in the genus
Equisetum. But there are some fossil
species
that are not assignable to the modern genus. Equisetites is a "wastebin taxon
" uniting all sorts of large horsetails from the Mesozoic
; it is almost certainly paraphyletic and would probably warrant to be 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 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.
Equisetales
The Equisetales is an order of pteridophytes with only one living genus Equisetum , of the family Equisetaceae. The fossil record includes additional extinct species in the Equisetaceae and the extinct families Calamitaceae and Archaeocalamitaceae....
, with one surviving genus, Equisetum, which comprises about twenty species.
Evolution and systematics
Equisetaceae is the only surviving family of the EquisetalesEquisetales
The Equisetales is an order of pteridophytes with only one living genus Equisetum , of the family Equisetaceae. The fossil record includes additional extinct species in the Equisetaceae and the extinct families Calamitaceae and Archaeocalamitaceae....
, a group with many fossils of large tree-like plants that possessed ribbed stems similar to modern horsetails. Pseudobornia
Pseudobornia
Pseudobornia is a genus of plants known only from fossils found from the Upper Devonian. It contains a single species Pseudobornia ursina, and is the earliest fossil assigned with certainty to the Sphenopsida....
is the oldest known relative of Equisetum; it grew in the late Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
, about 375 million years ago and is assigned to its own order.
All living horsetails are placed in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Equisetum. But there are some fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
that are not assignable to the modern genus. Equisetites is a "wastebin taxon
Wastebin taxon
Wastebasket taxon is a term used in some taxonomic circles to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined by their lack of one or more distinct character states or by their not belonging to one or more other taxa...
" uniting all sorts of large horsetails from the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
; it is almost certainly paraphyletic and would probably warrant to be 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
Secondary growth
In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length. As long as the lateral meristems...
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.