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Psilophyton
''Psilophyton'' is a genus (biology), genus of extinct vascular plants. Described in 1859, it was one of the first fossil plants to be found which was of Devonian age (about ). Specimens have been found in northern Maine, USA; Gaspé Bay, Quebec and New Brunswick, Canada; the Czech Republic; and Yunnan, China. Plants lacked leaves or true roots; spore-forming organs or Sporangium, sporangia were borne on the ends of branched clusters. It is significantly more complex than some other plants of comparable age (e.g. ''Rhynia'') and is thought to be part of the group from within which the modern ferns and seed plants evolved. Description Almost all the species of ''Psilophyton'' have been found in rocks of Emsian age (around ). One exception is ''P. krauselii'', from the Czech Republic, which is younger, being from the upper part of the Middle Devonian (around ). ''Psilophyton dawsonii'' is the best-known species. Compressed and mineralized specimens have been found in sever ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Psilophyton Dawsonii-rev
''Psilophyton'' is a genus (biology), genus of extinct vascular plants. Described in 1859, it was one of the first fossil plants to be found which was of Devonian age (about ). Specimens have been found in northern Maine, USA; Gaspé Bay, Quebec and New Brunswick, Canada; the Czech Republic; and Yunnan, China. Plants lacked leaves or true roots; spore-forming organs or Sporangium, sporangia were borne on the ends of branched clusters. It is significantly more complex than some other plants of comparable age (e.g. ''Rhynia'') and is thought to be part of the group from within which the modern ferns and seed plants evolved. Description Almost all the species of ''Psilophyton'' have been found in rocks of Emsian age (around ). One exception is ''P. krauselii'', from the Czech Republic, which is younger, being from the upper part of the Middle Devonian (around ). ''Psilophyton dawsonii'' is the best-known species. Compressed and mineralized specimens have been found in sever ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sawdonia
Sawdonia is an extinct genus of early vascular plants, known from the Upper Silurian to the Lower Carboniferous (). ''Sawdonia'' is best recognized by the large number of spikes (enations) covering the plant. These are vascular plants that do not have vascular systems in their enations. The first species of this genus (''Sawdonia ornata'') was described in 1859 by Sir J. William Dawson and, was originally attributed to the genus '' Psilophyton''. He named this plant ''Psilophyton princeps''. In 1971 Francis Hueber proposed a new genus for this species due to its "Divergent technical characters from the generic description for ''Psilophyton''." The holotype used for description is Dawson Collection Number 48, pro parte, Museum Specimen Number 3243. (See Dawson 1871, Plate IX, fig 101.) Sir J. William Dawson Collection, Peter Redpath Museum, McGill University, Montreal, Quebec, Canada. Morphology These plants are described by Hueber as having monopodially branched stems, that ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Psilotum
''Psilotum'' is a genus of fern-like vascular plants. It is one of two genera in the family Psilotaceae commonly known as whisk ferns, the other being ''Tmesipteris''. Plants in these two genera were once thought to be descended from the earliest surviving vascular plants, but more recent phylogenies place them as basal ferns, as a sister group to Ophioglossales. They lack true roots and leaves are very reduced, the stems being the organs containing photosynthetic and conducting tissue. There are only two species in ''Psilotum'' and a hybrid between the two. They differ from those in ''Tmesipteris'' in having stems with many branches and a synangium with three lobes rather than two. Description and life cycle Whisk ferns in the genus ''Psilotum'' lack true roots but are anchored by creeping rhizomes. The stems have many branches with paired enations, which look like small leaves but have no vascular tissue. Above these enations there are synangia formed by the fusion of three ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aarabia
''Aarabia'' is a genus of extinct vascular plants found in central Morocco in outcrops of Early Devonian age (Emsian, around ). The leafless plant has a complex branching system with a main stem and at least three orders of side branches. In addition to these long branches, stems bore very short branches, which typically branched once into two curved sections. Spore-forming organs or sporangia were borne singly on reduced lateral branches in groups of at least three. The genus is thought to be related to the euphyllophytes – modern ferns and seed plants. Description Fossils were found in an outcrop believed to be of Emsian age (around ) northwest of the town of Azrou in central Morocco. They were 'adpressions' – a mixture of compressed and chemically altered remains of the original plant and impressions of its shape. Only central parts of the plant were found, the longest being 9 cm. Stems (axes) were bare of leaves, spines or other protrusions, and were between 1.5 an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhynia
''Rhynia'' is a single-species genus of Devonian vascular plants. ''Rhynia gwynne-vaughanii'' was the sporophyte generation of a vascular, axial, free-sporing diplohaplontic embryophytic land plant of the Early Devonian that had anatomical features more advanced than those of the bryophytes. ''Rhynia gwynne-vaughanii'' was a member of a sister group to all other eutracheophytes, including modern vascular plants. Description ''Rhynia gwynne-vaughanii'' was first described as a new species by Robert Kidston and William H. Lang in 1917. The species is known only from the Rhynie chert in Aberdeenshire, Scotland, where it grew in the vicinity of a silica-rich hot spring. ''Rhynia'' was a vascular plant, and grew in association with other vascular plants such as '' Asteroxylon mackei'', a probable ancestor of modern clubmosses ( Lycopsida), and with pre-vascular plants such as ''Aglaophyton major'', which is interpreted as basal to true vascular plants. ''Rhynia'' is thought t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, where rocks from this period were first studied. The first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. The arthropod groups of myriapods, arachnids and hexapods also became well-established early in this period, after starting their expansion to land at least from the Ordovician period. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. The placoderms began dominat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xylem Development
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from the Ancient Greek word (''xylon''), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout a plant. The term was introduced by Carl Nägeli in 1858. Structure The most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called ''vessels''. Xylem also contains two other type of cells: parenchyma and fibers. Xylem can be found: * in vascular bundles, present in non-woody plants and non-woody parts of woody plants * in secondary xylem, laid down by a meristem called the vascular cambium in woody plants * as part of a stelar arrangement not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taeniocrada
''Taeniocrada'' is a genus of extinct plants of Devonian age (). It is used as a form genus for fossil plants with leafless flattened stems which divided dichotomously and had prominent midribs regarded as containing vascular tissues. It has been suggested that some species assigned to this genus were aquatic. Description Key features of the original definition of the genus ''Taeniocrada'' were that it possessed leafless flattened stems with prominent midribs which appeared to contain vascular tissues. As more species were added to the genus, its definition became less clear. Three of the better-known species are ''T. decheniana'', ''T. dubia'', and ''T. stilesvillensis''. ''Taeniocrada decheniana'', from the Lower Devonian, had separate fertile stems which repeatedly branched in a dichotomous fashion ending in sporangia between 3 and 7 mm long. A few sporangia were borne on the sides of stems. The species was found in dense stands. It has been suggested that it was aq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type (biology)
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the defining features of that particular taxon. In older usage (pre-1900 in botany), a type was a taxon rather than a specimen. A taxon is a scientifically named grouping of organisms with other like organisms, a set that includes some organisms and excludes others, based on a detailed published description (for example a species description) and on the provision of type material, which is usually available to scientists for examination in a major museum research collection, or similar institution. Type specimen According to a precise set of rules laid down in the International Code of Zoological Nomenclature (ICZN) and the International Code of Nomenclature for algae, fungi, and plants (ICN), the scientific name of every taxon is alm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vascular Tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: the vascular cambium and the cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant. The cells in vascular tissue are typically long and slender. Since the xylem and phloem function in the conduction of water, minerals, and nutrients throughout the plant, it is not surprising that their form should be similar to pipes. The individual cells of phloem are connected end-to-end, just as the sections of a pipe might be. As the plant grows, new vascular tissue differentiates in the growing tips of the plant. The new tissue is aligned with existing vascular tissue, maintaining its connection throughout the plant. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laurussia
Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pangaea, drifting farther north after the split and finally broke apart with the opening of the North Atlantic Ocean c. 56 Mya. The name is a portmanteau of Laurentia and Asia. Laurentia, Avalonia, Baltica, and a series of smaller terranes, collided in the Caledonian orogeny c. 400 Ma to form Laurussia (also known as Euramerica, or the Old Red Sandstone Continent). Laurussia then collided with Gondwana to form Pangaea. Kazakhstania and Siberia were then added to Pangaea 290–300 Ma to form Laurasia. Laurasia finally became an independent continental mass when Pangaea broke up into Gondwana and Laurasia. Terminology and origin of the concept Laurentia, the Palaeozoic core of North America and continental fragments that now mak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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