| Equisetopsida Fossil range: Late Devonian[1] to Recent |
||||||
|---|---|---|---|---|---|---|
 |
||||||
| Scientific classification | ||||||
|
||||||
| Orders | ||||||
|
||||||
| Synonyms | ||||||
|
Sphenopsida |
Equisetopsida, or Sphenopsida, is a class of plants with a fossil record going back to the Devonian. The Equisetales is an order of pteridophytes with only one living genus Equisetum (horsetails Calamitaceae is an extinct family of plants related to the modern Horsetail. Equisetum is a genus of Vascular plants that reproduce by spores rather than seeds In Scientific nomenclature, synonyms are different Scientific names used for a single Taxon. A class is the Taxonomic rank in the Biological classification of organisms in Biology below phylum and above order. Plants are living Organisms belonging to the kingdom Plantae. The Devonian is a geologic period and system of the Paleozoic era spanning from to million years ago. Living species are commonly known as horsetails[2] and typically grow in wet areas, with needle-like leaves radiating at regular intervals from a single vertical stem. Equisetopsida is placed in the botanical division of ferns (Pteridophyta),[3] though sometimes regarded as a separate division Equisetophyta (also as Sphenophyta or Arthrophyta). A fern is any one of a group of about 20000 Species of Plants classified in the phylum or division Pteridophyta, also known as Filicophyta
Contents |
Morphology
The Sphenophytes comprise photosynthesising, "segmented", hollow stems, sometimes filled with pith. At the junction ("node", see diagram) between each segment is a whorl of leaves. In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis. In the only extant genus Equisetum, these are small leaves (microphylls) with a singular vascular trace. Equisetum is a genus of Vascular plants that reproduce by spores rather than seeds terminology of fossil plants is in places a little confusing In the discipline's 200+ year history certain concepts have become entrenched even though improved understanding has threatened the However, sphenophyte leaves probably arose by the reduction of a megaphyll, as evidenced by early fossil forms such as Sphenophyllum, in which the leaves are broad with branching veins. terminology of fossil plants is in places a little confusing In the discipline's 200+ year history certain concepts have become entrenched even though improved understanding has threatened the [4] The plumbing of these leaves is interesting: the vascular traces trifurcate at the junctions, with one thread going to the microphyll, and the other two moving left and right to merge with the new branches of their neighbours. The vascular system itself curiously resembles that of the vascular plants' eustele, which evolved convergently. A primary xylem contains carinal canals; in the Calamitales, secondary xylem (but not secondary phloem) can be secreted as the cambium grows outwards, producing a woody stem, and allowing the plants to grow as high as 10m. Calamitaceae is an extinct family of plants related to the modern Horsetail. The cortex itself contains valecular canals; due to the softer nature of the phloem, these are very rarely seen in fossil instances.
The plant does not bear a coherent root system but underground rhizomes, from which roots and aerial axes emerge.
The plant contains an intercalary meristem: that is to say, each segment of the stem grows as the plant gets taller. This contrasts with the seed plants, which contain an apical meristem - i. e. new growth comes only from growing tips (and widening of stems). Growth was determinate - i. e. the plants' phenotype dictated a maximum height, which the plant would grow to then get no higher.
Sphenophytes bear cones (technically strobili, sing. strobilus) at the tips of some stems. These cones comprise spirally arranged sporophores, which bear spores in four clusters, and in extant sphenophytes cover the spores externally - like four sacs hanging from an umbrella, with its handle embedded in the central cone body. In extinct groups, further protection was afforded to the spores by the presence of whorls of bracts - big pointy microphylls protruding from the cone. In Botany, a bract is a modified or specialized Leaf. Bracts are ordinarily associated with reproductive structures (subtending Flowers Inflorescence
The spores themselves bear characteristic elaters, distinctive spring-like attachments which are hygroscopic: i. "Elaters" is also used as a common name for the Elateridae (click beetles Hygroscopy is the ability of a substance to attract Water Molecules from the surrounding environment through either absorption or Adsorption e. they change their configuration in the presence of water, helping the spores move and aiding their dispersal. Dispersal is aided in the first instance by laterally dehiscing sporangia, which pop open and scatter spores.
The extant horsetails are mostly homosporous, but this is conspicuously not the case in the past. In Biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions
Fossil record
The extant horsetails represent a tiny fraction of Sphenophyte diversity in the past. There were three orders of Equisetopsid; the Pseudoborniales, which first appeared in the late Devonian. The Devonian is a geologic period and system of the Paleozoic era spanning from to million years ago. [1] Second, the Sphenophyllales which were a dominant member of the Carboniferous understory, and prospered until the mid and early Permian respectively. 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 Equisetales is an order of pteridophytes with only one living genus Equisetum (horsetails Equisetum is a genus of Vascular plants that reproduce by spores rather than seeds
The organisms first appear in the fossil record during the late Devonian,[1] 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 the land for almost a hundred million years, with the first evidence of land plants dating to [5][6]
Systematics
The horsetails and their fossil relatives have long been recognized as quite distinct from other seedless vascular plants. Plants have evolved through increasing levels of complexity, from the earliest Algal mats through Bryophytes Lycopods Ferns [7] In fact, the group is so unlike other living and fossil plants that its relationship to other plants has long been considered problematic. [8]
Because of the unclear relationships of the group, the rank botanists assign to it varies from order to division. This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used When recognized as a separate division, the literature uses many possible names, including Arthrophyta[8], Sphenophyta[1][9], or Equisetophyta. Other authors have regarded 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[10] or Sphenopsida. [11]
References
- ^ a b c d Taylor, Thomas N. ; Edith L. Taylor. (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall, 303-305. ISBN 0-13-651589-4.
- ^ horsetail. Merriam-Webster Online Dictionary.
- ^ Smith, Alan R. ; Kathleen M. Pryer, Eric Schuettpelz, Petra Korall, Harald Schneider, & Paul G. Wolf (2006). "A classification for extant ferns". Taxon 55 (3): 705–731.
- ^ Rutishauser, R. (1999). "Polymerous Leaf Whorls in Vascular Plants: Developmental Morphology and Fuzziness of Organ Identities". International Journal of Plant Sciences 160 (6): 81-103. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ Wellman, C & Gray, J. (2003). "{{{title}}}". Science.
- ^ Gray, J. (1985). "{{{title}}}".
- ^ Eames, Arthur J. (1936). Morphology of Vascular Plants (Lower Groups). New York and London: McGraw-Hill Book Company, 110-115.
- ^ a b Bold; C. J. Alexopoulos, & T. Delevoryas (1987). Morphology of Plants and Fungi, 5th edition, New York: Harper-Collins, 371-387, 478, 506-514. ISBN 0-06-040838-1.
- ^ Gifford, Ernest M. ; Adriance S. Foster (1988). Morphology and Evolution of Vascular Plants, 3rd, New York: W. H. Freeman and Company, 175-207. ISBN 0-7167-1946-0.
- ^ Kenrick, Paul; Peter R. Crane (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Smithsonian Institution Press, 241-242. ISBN 1-56098-730-8.
- ^ Stewart, Wilson N. ; Gar W. Rothwell (1993). Paleobotany and the Evolution of Plants, 2nd edition, Cambridge: Cambridge University Press. Cambridge University Press (known colloquially as CUP is a Publisher given a Royal Charter by Henry VIII in 1534 ISBN 0-521-38294-7.
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic