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Gnetales
Gnetophyta () is a division of plants (alternatively considered the subclass Gnetidae or order Gnetales), grouped within the gymnosperms (which also includes conifers, cycads, and ginkgos), that consists of some 70 species across the three Relict (biology), relict genus, genera: ''Gnetum'' (Family (biology), family Gnetaceae), ''Welwitschia'' (family Welwitschiaceae), and ''Ephedra (genus), Ephedra'' (family Ephedraceae). The earliest unambiguous records of the group date to the Jurassic, and they achieved their highest diversity during the Early Cretaceous. The primary difference between gnetophytes and other gymnosperms is the presence of vessel elements, a system of small tubes (xylem) that transport water within the plant, similar to those found in flowering plants. Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have brought this hypothesis into question, with many recent phylogenies f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Welwitschiaceae
Welwitschiaceae is a family of plants of the order Gnetales with one living species, '' Welwitschia mirabilis'', found in southwestern Africa. Three fossil genera have been recovered from the Crato Formation – late Aptian ( Lower Cretaceous) strata located in the Araripe Basin in northeastern Brazil, with one of these also being known from the early Late Cretaceous (Cenomanian-Turonian) Akrabou Formation of Morocco. Taxonomy German naturalist Friedrich Markgraf coined the name Welwitschiaceae in 1926, which appeared in '' Die Natürlichen Pflanzenfamilien''. Most recent systems place the Welwitschiaceae in the gymnosperm order Gnetales. This order is most closely related to the order Pinales, which includes all extant conifers. Genetic analyses indicate that the Gnetales arose from within the conifer group, and any morphological similarities between angiosperms and Gnetales have evolved separately. The ancestors of the extant gymnosperm orders—Gnetales, Coniferales, Cy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gnetaceae
''Gnetum'' is a genus of gymnosperms, the sole genus in the family Gnetaceae within the Gnetophyta. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been proposed to have been the first plants to be insect-pollinated as their fossils occur in association with extinct pollinating scorpionflies. Molecular phylogenies based on nuclear and plastid sequences from most of the species indicate hybridization among some of the Southeast Asian species. Fossil-calibrated molecular-clocks suggest that the ''Gnetum'' lineages now found in Africa, South America and Southeast Asia are the result of ancient long-distance dispersal across seawater. Their leaves are rich in phytochemicals such as flavonoids and stilbenes. Of the species studied so far, ''Gnetum'' have photosynthetic and transpiration capacities which are considerably lower than those of other seed plants, due to the absence of multiple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ephedra (genus)
''Ephedra'' is a genus of gymnosperm shrubs. there were 77 recognized species. The various species of ''Ephedra'' are widespread in many arid regions of the world, ranging across southwestern North America, southern Europe, northern Africa, southwest and central Asia, northern China, and western South America. It is the only extant genus in its family, Ephedraceae, and order, Ephedrales, and one of the three living members of the division Gnetophyta alongside '' Gnetum'' and '' Welwitschia.'' In temperate climates, most ''Ephedra'' species grow on shores or in sandy soils with direct sun exposure. Common names in English include joint-pine, jointfir, Mormon-tea, or Brigham tea. The Chinese name for ''Ephedra'' species is ''mahuang'' (). ''Ephedra'' is the origin of the name of the stimulant ephedrine, which the plants contain in significant concentration. Description The family Ephedraceae, of which ''Ephedra'' is the only extant genus, are gymnosperms, and generally shr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gymnosperm
The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetophyta, gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in ( and ), and literally means 'naked seeds'. The name is based on the unenclosed condition of their seeds (called ovules in their unfertilized state). The non-encased condition of their seeds contrasts with the seeds and ovules of flowering plants (angiosperms), which are enclosed within an Ovary (botany), ovary. Gymnosperm seeds develop either on the surface of scales or Leaf, leaves, which are often modified to form Conifer cone, cones, or on their own as in Taxus, yew, ''Torreya'', and ''Ginkgo''. The life cycle of a gymnosperm involves alternation of generations, with a dominant diploid sporophyte phase, and a reduced haploid gam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ephedra (plant)
''Ephedra'' is a genus of gymnosperm shrubs. there were 77 recognized species. The various species of ''Ephedra'' are widespread in many arid regions of the world, ranging across southwestern North America, southern Europe, northern Africa, southwest and central Asia, northern China, and western South America. It is the only extant genus in its family, Ephedraceae, and order, Ephedrales, and one of the three living members of the division Gnetophyta alongside ''Gnetum'' and ''Welwitschia.'' In temperate climates, most ''Ephedra'' species grow on shores or in sandy soils with direct sun exposure. Common names in English include joint-pine, jointfir, Mormon-tea, or Brigham tea. The Chinese name for ''Ephedra'' species is ''mahuang'' (). ''Ephedra'' is the origin of the name of the stimulant ephedrine, which the plants contain in significant concentration. Description The family Ephedraceae, of which ''Ephedra'' is the only extant genus, are gymnosperms, and generally shrubs, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gnetum Gnemon Male
''Gnetum'' is a genus of gymnosperms, the sole genus in the family Gnetaceae within the Gnetophyta. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been proposed to have been the first plants to be insect-pollinated as their fossils occur in association with extinct pollinating scorpionflies. Molecular phylogenies based on nuclear and plastid sequences from most of the species indicate hybridization among some of the Southeast Asian species. Fossil-calibrated molecular-clocks suggest that the ''Gnetum'' lineages now found in Africa, South America and Southeast Asia are the result of ancient long-distance dispersal across seawater. Their leaves are rich in phytochemicals such as flavonoids and stilbenes. Of the species studied so far, ''Gnetum'' have photosynthetic and transpiration capacities which are considerably lower than those of other seed plants, due to the absence of multiple chlo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vessel Element
A vessel element or vessel member (also called a xylem vessel) is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are found in most angiosperms (flowering plants) and in some gymnosperms such as cycads and ''Ephedra (plant), Ephedra'', but absent in conifers. Vessel elements are the main feature distinguishing the "hardwood" of angiosperms from the "softwood" of conifers. Anatomy Xylem is the tissue in vascular plants that conducts water (and substances dissolved in it) upwards from the roots to the shoots. Two kinds of cell are involved in xylem transport: tracheids and vessel elements. Vessel elements are the building blocks of vessels, the conducting pathways that constitute the major part of the water transporting system in flowering plants. Vessels form an efficient system for transporting water (including necessary minerals) from the root to the leaves and other parts of the plant. In secondary xylem – the xylem that is prod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycad
Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow slowly and have long lifespans. Because of their superficial resemblance to Arecaceae, palms or ferns, they are sometimes mistaken for them, but they are not closely related to either group. Cycads are gymnosperms (naked-seeded), meaning their fertilization, unfertilized seeds are open to the air to be directly fertilized by pollination, as contrasted with angiosperms, which have enclosed seeds with more complex fertilization arrangements. Cycads have very specialized pollinators, usually a specific beetle, and more rarely a thrips or a moth. Both male and female cycads bear cones (strobilus, stro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. The Jurassic constitutes the second and middle period of the Mesozoic, Mesozoic Era as well as the eighth period of the Phanerozoic, Phanerozoic Eon and is named after the Jura Mountains, where limestone strata from the period were first identified. The start of the Jurassic was marked by the major Triassic–Jurassic extinction event, associated with the eruption of the Central Atlantic magmatic province, Central Atlantic Magmatic Province (CAMP). The beginning of the Toarcian Age started around 183 million years ago and is marked by the Toarcian Oceanic Anoxic Event, a global episode of Anoxic event, oceanic anoxia, ocean acidification, and elevated global temperatures associated with extinctions, likely caused by the eruption of the Kar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ephedraceae
Ephedraceae is a family of gymnosperms belonging to Gnetophyta, it contains only a single extant genus, ''Ephedra (plant), Ephedra'', as well as a number of extinct genera from the Early Cretaceous. Taxonomy File:Eamesia chinensis.png, ''Eamesia,'' showing male cone (B) File:Chengia laxispicatagen.webp, ''Chengia'', showing female reproductive spike (B) File:Jianchangia verticillata.webp, ''Jianchangia'', showing chlamydosperms (C) and ovulate cone (F) File:Arlenea diagram.jpg, Diagram of ''Arlenea,'' showing closeup of terminal region with female reproductive structures (B) and cross section of a female reproductive structure.(C) Ephedraceae is agreed to be the most Basal (phylogenetics), basal group amongst extant gnetophytes. Members of the family typically grow as shrubs and have small, linear leaves that possess parallel veins. The fossil Ephedraceae genera show a range of morphologies transitional between the ancestral Glossary of botanical terms#lax, lax male and female ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
