The plant Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004, division Gnetophyta or gnetophytes comprise three related families of woody plants A woody plant is a plant that uses wood as a structural tissue. They are typically perennial plants that have their stems and larger roots reinforced with wood produced adjacent to the vascular tissues: typically the main stem and larger branches and roots are covered by a layer of thickened bark. Woody plants are usually either trees, shrubs, or grouped in the gymnosperms The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds (called ovules in their unfertilized state). Their naked condition stands in contrast to the. The gnetophytes differ from other gymnosperms in having vessel elements A vessel element is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are typically found in the angiosperms but absent from most gymnosperms such as the conifers as in the flowering plants The flowering plants or angiosperms are the most diverse group of land plants. The flowering plants and the gymnosperms are the only extant groups of seed plants. The flowering plants are distinguished from other seed plants by a series of apomorphies, or derived characteristics.
The living Gnetophyta comprise three genera:
- Gnetum Gnetum is a genus of about 30-35 species of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms they possess vessel elements in the xylem
- Welwitschia Welwitschia is a monotypic genus of gymnosperm plant, composed solely of the very distinct Welwitschia mirabilis. It is the only genus of the family Welwitschiaceae, in the order Welwitschiales, in the division Gnetophyta. The plant is named after the Austrian botanist Friedrich Welwitsch who discovered it in 1859 and is considered a living fossil
- Ephedra Ephedra is a genus of gymnosperm shrubs, the only genus in the family Ephedraceae and order Ephedrales. These plants occur in dry climates over a wide area mainly in the northern hemisphere, across southern Europe, north Africa, southwest and central Asia, southwestern North America, and, in the southern hemisphere, in South America south to
Gnetum Gnetum is a genus of about 30-35 species of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms they possess vessel elements in the xylem species are mostly woody Wood is an organic material; in the strict sense wood is produced as secondary xylem in the stems of trees . In a living tree it transfers water and nutrients to the leaves and other growing tissues, and has a support function, enabling woody plants to reach large sizes or to stand up for themselves. However, wood may also refer to other plant climbers The term vine may refer to a climbing or trailing plant. The word, derived from Latin vīnea, in the original sense referred to the grapevines . The modern extended sense is mostly restricted to North American English, which uses "grapevine" to refer to the grape-bearing Vitis species. British English tends to use "climber" to in tropical forests. However, the most well-known member of this group, Gnetum gnemon Gnetum gnemon is a species of Gnetum native to southeast Asia and the western Pacific Ocean islands, from Assam south and east through Indonesia and Malaysia to the Philippines and Fiji. Common names include Melinjo or Belinjo , Bago (Malay language, Tagalog language), Peesae (Thai language), dae (Kwara'ae language) and Bét, Rau bép, Rau danh or, is a tree. Its seeds are used to produce a crispy krupuk Krupuk, kerupuk, or kroepoek in Indonesia; keropok in Malaysia; kropek in the Philippines; bánh phồng tôm in Vietnam; prawn crackers in British English, shrimp chips or shrimp crackers in American English; is a popular snack in parts of East and Southeast Asia. Krupuk are deep fried crackers made from prawns and starch snack known as emping or krupuk belinjo.
Welwitschia Welwitschia is a monotypic genus of gymnosperm plant, composed solely of the very distinct Welwitschia mirabilis. It is the only genus of the family Welwitschiaceae, in the order Welwitschiales, in the division Gnetophyta. The plant is named after the Austrian botanist Friedrich Welwitsch who discovered it in 1859 and is considered a living fossil comprises only one species, Welwitschia mirabilis. It grows only in the deserts of Namibia Namibia, officially the Republic of Namibia , is a country in Southern Africa whose western border is the Atlantic Ocean. It shares borders with Angola and Zambia to the north, Botswana and Zimbabwe to the east, and South Africa to the south and east. It gained independence from South Africa on 21 March 1990 following the Namibian War of and Angola Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean. The exclave province of Cabinda has a border with the Republic of the Congo and the Democratic Republic of the Congo. The plant is strange in having only two large strap-like leaves for all its life. These grow continuously from the base, and are usually tattered at the ends by flapping in the winds.
Plants of the genus Ephedra Ephedra is a genus of gymnosperm shrubs, the only genus in the family Ephedraceae and order Ephedrales. These plants occur in dry climates over a wide area mainly in the northern hemisphere, across southern Europe, north Africa, southwest and central Asia, southwestern North America, and, in the southern hemisphere, in South America south to are known as jointfirs because they have long slender branches which bear tiny scale-like leaves at their nodes. Ephedra has been traditionally used as a stimulant Stimulants, also sometimes called psychostimulants, are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others. Due to their effects typically having an "up" quality to them,, but is a controlled substance A controlled substance is generally a drug or chemical whose manufacture, possession, and use are regulated by a government. This may include illegal drugs and prescription medications today in many jurisdictions because of the risk of harmful or even fatal overdosing The term drug overdose describes the ingestion or application of a drug or other substance in quantities greater than are recommended or generally practiced. An overdose is widely considered harmful and dangerous as it can result in death.
In some classifications all three genera are placed in a single order (Gnetales) but in others distributed among three orders, each containing a single family and genus.
Gnetum and Welwitschia diverged from each other more recently than from Ephedra.[1]
Knowledge of fossils of the gnetophytes has increased greatly since the 1980s.[1] There are fossils from the Permian The Permian[note 1] is a geologic period and system characterized by widespread, diverse and maturing lifeforms which comes just after the Carboniferous and that extends from 299.0 ± 0.8 to 251.0 ± 0.4 Ma . It is the last period of the Paleozoic Era and famous for its ending epoch event, the largest mass extinction known to science. The Permian,[2] the Triassic The Triassic is a geologic period and system that extends from about 251 to 199 Ma . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events. The extinction event that closed the Triassic period has recently been more, and the Jurassic The Jurassic is a geologic period and system that extends from about 199.6± 0.6 Ma to 145.5± 4 Ma, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Reptiles". The start of the period is marked by the major Triassic– which may belong to the gnetophytes, but this is uncertain.[3] The fossil record is richer starting in the early Cretaceous The Cretaceous , Latin language for "chalky", usually abbreviated K for its German translation Kreide (chalk), is a geologic period and system from circa 145.5 ± 4 to 65.5 ± 0.3 million years ago (Ma). In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period of the Cenozoic era, with fossils of plants as well as seeds A seed ( /ˈsiːd/ ), referred to as a kernel in some plants, is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant. The formation of the seed completes and pollen Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the female cone of coniferous plants. When pollen lands which can be clearly assigned to the gnetophytes.[3]
Molecular phylogenies of extant gymnosperms have conflicted with morphological characters with regard to whether the gymnosperms as a whole (including gnetophytes) comprise a monophyletic group A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[note 1] or a paraphyletic In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all the descendants of that ancestor one that gave rise to angiosperms. At issue is whether the Gnetophyta are the sister group Cladistics is a form of biological systematics which classifies living organisms on the basis of shared ancestry. It can be distinguished from other taxonomic systems, such as phenetics, by its focus on evolutionary relationships; while other systems usually use morphological similarities to group similar species into genera, families and other of angiosperms The flowering plants or angiosperms are the most diverse group of land plants. The flowering plants and the gymnosperms are the only extant groups of seed plants. The flowering plants are distinguished from other seed plants by a series of apomorphies, or derived characteristics, or whether they are sister to, or nested within, other extant gymnosperms. Numerous fossil gymnosperm clades once existed that are morphologically at least as distinctive as the four living gymnosperm The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds (called ovules in their unfertilized state). Their naked condition stands in contrast to the groups, such as Bennettitales Bennettitales is an extinct order of seed plants that first appeared in the Triassic period and became extinct toward the end of the Cretaceous. Some were characterized by thick trunks and pinnately compound leaves that bore a superficial resemblance to those of cycads, differing primarily in stomatal arrangement, Caytonia and the glossopterids. When these gymnosperm fossils are considered the question of gnetophyte relationships to other seed plants becomes even more complicated.
References
- ^ a b Peter R. Crane, Patrick Herendeen and Else Marie Friis (2004). "Fossils and plant phylogeny". American Journal of Botany 91: 1683–1699. doi The Digital Object Identifier System is a managed system for persistent identification of content-related entities on digital networks. These entities may be content items (digital files, physical objects, abstract works), or any related entities in a content transaction (e.g. licenses, parties, etc.). "DOI" is sometimes used to mean the:10.3732/ajb.91.10.1683. http://www.amjbot.org/cgi/content/full/91/10/1683.
- ^ Zi-Qiang Wang (2004). "A New Permian Gnetalean Cone as Fossil Evidence for Supporting Current Molecular Phylogeny". Annals of Botany 94 (2): 281–288. doi The Digital Object Identifier System is a managed system for persistent identification of content-related entities on digital networks. These entities may be content items (digital files, physical objects, abstract works), or any related entities in a content transaction (e.g. licenses, parties, etc.). "DOI" is sometimes used to mean the:10.1093/aob/mch138. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 15229124. http://aob.oxfordjournals.org/cgi/content/full/94/2/281.
- ^ a b Catarina Rydin, Kaj Raunsgaard Pedersen, Peter R. Crane and Else Marie Friis (2006). "Former Diversity of Ephedra (Gnetales): Evidence from Early Cretaceous Seeds from Portugal and North America". Annals of Botany 98 (1): 123–140. doi The Digital Object Identifier System is a managed system for persistent identification of content-related entities on digital networks. These entities may be content items (digital files, physical objects, abstract works), or any related entities in a content transaction (e.g. licenses, parties, etc.). "DOI" is sometimes used to mean the:10.1093/aob/mcl078. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 16675607. http://aob.oxfordjournals.org/cgi/content/full/98/1/123.
- Burleigh, J. G., and S. Mathews. 2004. Phylogenetic signal in nucleotide data from seed plants: implications for resolving the seed plant tree of life. American Journal of Botany 91: 1599-1613 (abstract)
- Gifford, Ernest M., Adriance S. Foster. 1989. Morphology and Evolution of Vascular Plants. Third edition. WH Freeman and Company, New York.
- Hilton, Jason, and Richard M. Bateman. 2006. Pteridosperms are the backbone of seed-plant phylogeny. Journal of the Torrey Botanical Society 133: 119-168 (abstract)
Categories: Gnetophyta
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e-ciencia.com, Spain
Este es el caso de una Gimnosperma del Phylum Gnetophyta y en concreto del orden de las Welwitchiales. Dentro de este orden tenemos la familia Welwitchia representada por una sola especie Welwitchia mirabilis. Esta planta vive en el desierto de Namibia ...
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a Gymnosperms Extant groups Ginkgo fruit Cycads Gnetophyta
Q. 1.Anthophyta 2. Coniferophyta 3. Cycadophyta 4. Gnetophyta 5. Ginkgophyta
Asked by Model - Tue Apr 21 21:51:15 2009 - - 1 Answers - 0 Comments
A. Cycads and the ginkgo are dioecious, meaning they are sexually reproducing. Conifers reproduce sexually and possibly asexually.
Answered by NJJ - Tue Apr 21 22:48:06 2009
