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26-565: See text. Equisetidae is one of the four subclasses of Polypodiopsida (ferns), a group of vascular plants with a fossil record going back to the Devonian . They are commonly known as horsetails . They typically grow in wet areas, with whorls of needle-like branches radiating at regular intervals from a single vertical stem. The Equisetidae were formerly regarded as a separate division of spore plants and called Equisetophyta , Arthrophyta , Calamophyta or Sphenophyta . When treated as

52-466: A convenient "artificial key" according to his Systema Sexuale , largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the APG system in 1998, which proposed a taxonomy of the flowering plants up to the level of orders, many sources have preferred to treat ranks higher than orders as informal clades . Where formal ranks have been assigned,

78-504: A class, the names Equisetopsida s.s. and Sphenopsida have also been used. They are now recognized as rather close relatives of the ferns (Polypodiopsida) of which they form a specialized lineage. However, the division between the horsetails and the other ferns is so ancient that many botanists, especially paleobotanists, still regard this group as fundamentally separate at the higher level. The horsetails comprise photosynthesising, "segmented", hollow stems, sometimes filled with pith. At

104-469: A single extant order, Equisetales . This order consists of a single monotypic family, Equisetaceae , with one genus Equisetum . Equisetum has about 20 species. 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 . The Sphenophyllales were a dominant member of

130-566: Is an antiquated remnant of the obsolete scala naturae , and the term is generally considered to be unscientific. Botanists define vascular plants by three primary characteristics: Cavalier-Smith (1998) treated the Tracheophyta as a phylum or botanical division encompassing two of these characteristics defined by the Latin phrase "facies diploida xylem et phloem instructa" (diploid phase with xylem and phloem). One possible mechanism for

156-521: Is to say a particular layout of organ systems. This said, the composition of each class is ultimately determined by the subjective judgment of taxonomists . In the first edition of his Systema Naturae (1735), Carl Linnaeus divided all three of his kingdoms of nature ( minerals , plants , and animals ) into classes. Only in the animal kingdom are Linnaeus's classes similar to the classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide

182-668: The Carboniferous understory, and prospered until the mid and early Permian . The Equisetales existed alongside the Sphenophyllales , but diversified as that group disappeared into extinction, gradually dwindling in diversity to today's single genus Equisetum . The organisms first appear in the fossil record during the late Devonian, a time when land plants were undergoing a rapid diversification, with roots, seeds and leaves having only just evolved. (See Evolutionary history of plants ) However, plants had already been on

208-467: The ferns (Polypodiopsida). Before the advent of modern molecular studies , the relationship of this group to other living and fossil plants was considered problematic. Because of their unclear relationships, the rank botanists assigned to the horsetails varied from order to division . When recognized as a separate division, the literature uses many possible names, including Arthrophyta, Calamophyta, Sphenophyta, or Equisetophyta. Other authors regarded

234-481: The molecular phylogenetic era, and considered the ferns (monilophytes), to comprise four classes , with the horsetails as class Equisetopsida sensu stricto . (This distinction is necessary because of the alternative usage of Equisetopsida sensu lato as a synonym for all land plants (Embryophyta) with rank of class.) Chase and Reveal (2009) treated the horsetails as subclass Equisetidae of class Equisetopsida sensu lato . The consensus classification produced by

260-508: The "true" tracheophytes, the eutracheophytes. † Aglaophyton † Horneophytopsida † Rhyniophyta Lycopodiophyta † Zosterophyllophyta † Cladoxylopsida Equisetopsida (horsetails) Marattiopsida Psilotopsida (whisk ferns and adders'-tongues) Pteridopsida (true ferns) † Progymnospermophyta Cycadophyta (cycads) Ginkgophyta (ginkgo) Gnetophyta Pinophyta (conifers) Magnoliophyta (flowering plants) † Pteridospermatophyta (seed ferns) This phylogeny

286-525: The Pteridophyte Phylogeny Group in 2016 also places horsetails in the subclass Equisetidae, but in the class Polypodiopsida (ferns broadly defined). The following diagram shows a likely phylogenic relationship between subclass Equisetidae and the other fern subclasses according to the Pteridophyte Phylogeny Group. Equisetidae (horsetails) Ophioglossidae Marattiidae Polypodiidae A 2018 study by Elgorriaga et al. suggests

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312-399: The ability to grow independent roots, woody structure for support, and more branching. A proposed phylogeny of the vascular plants after Kenrick and Crane 1997 is as follows, with modification to the gymnosperms from Christenhusz et al. (2011a), Pteridophyta from Smith et al. and lycophytes and ferns by Christenhusz et al. (2011b) The cladogram distinguishes the rhyniophytes from

338-484: The ability to produce secondary growth. The underground parts of the plants consist of jointed rhizomes , from which roots and aerial axes emerge. The plants have intercalary meristems in each segment of the stem and rhizome that grow as the plant gets taller. This contrasts with most seed plants, which grow from an apical meristem - i.e. new growth comes only from growing tips (and widening of stems). Horsetails bear cones (technically strobili , sing. strobilus ) at

364-420: The classification of plants that appeared in his Eléments de botanique of 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct grade of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct type of construction, which

390-563: The cone. The extant horsetails are homosporous , but extinct heterosporous species such as Calamostachys casheana appear in the fossil record. The sporangia open by lateral dehiscence to release the spores. The spores bear characteristic elaters , distinctive spring-like attachments which are hygroscopic : i.e. they change their configuration in the presence of water, helping the spores move and aiding their dispersal. The horsetails and their fossil relatives have long been recognized as distinct from other seedless vascular plants , such as

416-466: The junction ("node", see diagram) between each segment is a whorl of leaves . In the only extant genus Equisetum , these are small leaves ( microphylls ) with a singular vascular trace, fused into a sheath at each stem node. However, the leaves of Equisetum probably arose by the reduction of megaphylls , as evidenced by early fossil forms such as Sphenophyllum , in which the leaves are broad with branching veins. The vascular bundles trifurcate at

442-447: The land for almost a hundred million years, with the first evidence of land plants dating to 475  million years ago . [REDACTED] Data related to Equisetopsida at Wikispecies Class (biology) The class as a distinct rank of biological classification having its own distinctive name – and not just called a top-level genus (genus summum) – was first introduced by French botanist Joseph Pitton de Tournefort in

468-416: The nodes, with the central branch becoming the vein of a microphyll, and the other two moving left and right to merge with the new branches of their neighbours. The vascular system itself resembles that of the vascular plants' eustele , which evolved independently and convergently . Very rapid internode elongation results in the formation of a pith cavity and a ring of carinal canals formed by disruption of

494-473: The plant. They also have a specialized non-lignified tissue (the phloem ) to conduct products of photosynthesis . The group includes most land plants ( c.  300,000 accepted known species) other than mosses . Vascular plants include the clubmosses , horsetails , ferns , gymnosperms (including conifers ), and angiosperms ( flowering plants ). They are contrasted with nonvascular plants such as mosses and green algae . Scientific names for

520-421: The presumed evolution from emphasis on haploid generation to emphasis on diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. Elaboration of the spore stalk enabled the production of more spores and the development of the ability to release them higher and to broadcast them further. Such developments may include more photosynthetic area for the spore-bearing structure,

546-486: The primary xylem . Similar spaces, the vallecular canals are formed in the cortex. Due to the softer nature of the phloem, these are very rarely seen in fossil instances. In the Calamitaceae , secondary xylem (but not secondary phloem ) was secreted as the cambium grew outwards, producing a woody stem, and allowing the plants to grow as high as 10m. All extant species of Equisetum are herbaceous, and have lost

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572-967: The ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders. The class was considered the highest level of the taxonomic hierarchy until George Cuvier 's embranchements , first called Phyla by Ernst Haeckel , were introduced in the early nineteenth century. Vascular plant Vascular plants (from Latin vasculum  'duct'), also called tracheophytes ( UK : / ˈ t r æ k iː ə ˌ f aɪ t s / , US : / ˈ t r eɪ k iː ə ˌ f aɪ t s / ) or collectively tracheophyta ( / ˌ t r eɪ k iː ˈ ɒ f ɪ t ə / ; from Ancient Greek τραχεῖα ἀρτηρία ( trakheîa artēría )  'windpipe' and φυτά ( phutá )  'plants'), are plants that have lignified tissues (the xylem ) for conducting water and minerals throughout

598-536: The relationships within the Equisetidae are as shown in the following cladogram. † Sphenophyllales † Archaeocalamitaceae A.G. clade († Paracalamitina , † Cruciaetheca ) † Calamitaceae † Neocalamitaceae Equisetaceae According to the study, the age of the crown group of Equisetum dates at least to the Early Cretaceous , and most probably up to the Jurassic . Subclass Equisetidae contains

624-520: The same group as a class, either within a division consisting of the vascular plants or, more recently, within an expanded fern group. When ranked as a class, the group has been termed the Equisetopsida or Sphenopsida. Modern phylogenetic analysis , back to 2001, demonstrated that horsetails belong firmly within the fern clade of vascular plants . Smith et al. (2006) carried out the first higher-level pteridophyte classification published in

650-406: The tips of some stems. These cones comprise spirally arranged sporangiophores , which bear sporangia at their edges, and in extant horsetails cover the spores externally - like sacs hanging from an umbrella, with its handle embedded in the axis of the cone. In extinct groups, further protection was afforded to the spores by the presence of whorls of bracts - big pointed microphylls protruding from

676-463: The vascular plants group include Tracheophyta, Tracheobionta and Equisetopsida sensu lato . Some early land plants (the rhyniophytes ) had less developed vascular tissue; the term eutracheophyte has been used for all other vascular plants, including all living ones. Historically, vascular plants were known as " higher plants ", as it was believed that they were further evolved than other plants due to being more complex organisms. However, this

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