In the fields of horticulture and botany, the term deciduous means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves in the autumn. The term deciduous means "the dropping of a part, no longer needed" and the "falling away after its purpose is finished". In plants, it is the result of natural processes. "Deciduous" has a similar meaning when referring to animal parts, such as deciduous antlers in deer, deciduous teeth in some mammals. Wood from deciduous trees is used in a variety of ways in several industries including lumber for furniture and flooring, bowling pins and baseball bats and furniture, cabinets and paneling. In botany and horticulture, deciduous plants, including trees and herbaceous perennials, are those that lose all of their leaves for part of the year; this process is called abscission. In some cases leaf loss coincides with winter -- namely in polar climates. In other parts of the world, including tropical and arid regions, plants lose their leaves during the dry season or other seasons, depending on variations in rainfall.
The converse of deciduous is evergreen, where foliage is shed on a different schedule from deciduous trees, therefore appearing to remain green year round. Plants that are intermediate may be called semi-deciduous. Other plants are semi-evergreen and lose their leaves before the next growing season, retaining some during winter or dry periods; some trees, including a few species of oak, have desiccated leaves that remain on the tree through winter. Many deciduous plants flower during the period when they are leafless, as this increases the effectiveness of pollination; the absence of leaves improves wind transmission of pollen for wind-pollinated plants and increases the visibility of the flowers to insects in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry season regions, result in water stress on the plant. There is much less branch and trunk breakage from glaze ice storms when leafless, plants can reduce water loss due to the reduction in availability of liquid water during cold winter days.
Leaf drop or abscission involves complex physiological changes within plants. The process of photosynthesis degrades the supply of chlorophylls in foliage; when autumn arrives and the days are shorter or when plants are drought-stressed, deciduous trees decrease chlorophyll pigment production, allowing other pigments present in the leaf to become apparent, resulting in non-green colored foliage. The brightest leaf colors are produced when days grow short and nights are cool, but remain above freezing; these other pigments include carotenoids that are yellow and orange. Anthocyanin pigments produce red and purple colors, though they are not always present in the leaves. Rather, they are produced in the foliage in late summer, when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright autumn colors are limited to locations where days become short and nights are cool. In other parts of the world, the leaves of deciduous trees fall off without turning the bright colors produced from the accumulation of anthocyanin pigments.
The beginnings of leaf drop starts when an abscission layer is formed between the leaf petiole and the stem. This layer is formed in the spring during active new growth of the leaf; the cells are sensitive to a plant hormone called auxin, produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of the plant, the cells of the abscission layer remain connected; the elongation of these cells break the connection between the different cell layers, allowing the leaf to break away from the plant. It forms a layer that seals the break, so the plant does not lose sap. A number of deciduous plants remove nitrogen and carbon from the foliage before they are shed and store them in the form of proteins in the vacuoles of parenchyma cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new leaves or flowers. Plants with deciduous foliage have advantages and disadvantages compared to plants with evergreen foliage.
Since deciduous plants lose their leaves to conserve water or to better survive winter weather conditions, they must regrow new foliage during the next suitable growing season. Evergreens suffer greater water loss during the winter and they can experience greater predation pressure when small. Losing leaves in winter may reduce damage from insects. Removing leaves reduces cavitation which can damage xylem vessels in plants; this allows deciduous plants to have xylem vessels with larger diameters and therefore a greater rate of transpiration during the summer growth period
Delaware is one of the 50 states of the United States, in the South-Atlantic or Southern region. It is bordered to the south and west by Maryland, north by Pennsylvania, east by New Jersey and the Atlantic Ocean; the state takes its name from Thomas West, 3rd Baron De La Warr, an English nobleman and Virginia's first colonial governor. Delaware occupies the northeastern portion of the Delmarva Peninsula. It's the sixth most densely populated. Delaware's largest city is Wilmington; the state is divided into the lowest number of any state. From north to south, they are New Castle County, Kent County, Sussex County. While the southern two counties have been predominantly agricultural, New Castle County is more industrialized. Before its coastline was explored by Europeans in the 16th century, Delaware was inhabited by several groups of Native Americans, including the Lenape in the north and Nanticoke in the south, it was colonized by Dutch traders at Zwaanendael, near the present town of Lewes, in 1631.
Delaware was one of the 13 colonies participating in the American Revolution. On December 7, 1787, Delaware became the first state to ratify the Constitution of the United States, has since been known as "The First State"; the state was named after the Delaware River, which in turn derived its name from Thomas West, 3rd Baron De La Warr, the ruling governor of the Colony of Virginia at the time Europeans first explored the river. The Delaware Indians, a name used by Europeans for Lenape people indigenous to the Delaware Valley derive their name from the same source; the surname de La Warr is of Anglo-Norman origin. It came from a Norman lieu-dit La Guerre; this toponymic could derive from the Latin word ager, from the Breton gwern or from the Late Latin varectum. The toponyms Gara, Gaire appear in old texts cited by Lucien Musset, where the word gara means gore, it could be linked with a patronymic from the Old Norse verr. Delaware is 96 miles long and ranges from 9 miles to 35 miles across, totaling 1,954 square miles, making it the second-smallest state in the United States after Rhode Island.
Delaware is bounded to the north by Pennsylvania. Small portions of Delaware are situated on the eastern side of the Delaware River sharing land boundaries with New Jersey; the state of Delaware, together with the Eastern Shore counties of Maryland and two counties of Virginia, form the Delmarva Peninsula, which stretches down the Mid-Atlantic Coast. The definition of the northern boundary of the state is unusual. Most of the boundary between Delaware and Pennsylvania was defined by an arc extending 12 miles from the cupola of the courthouse in the city of New Castle; this boundary is referred to as the Twelve-Mile Circle. Although the Twelve-Mile Circle is claimed to be the only territorial boundary in the United States, a true arc, the Mexican boundary with Texas includes several arcs, many cities in the South have circular boundaries; this border extends all the way east to the low-tide mark on the New Jersey shore continues south along the shoreline until it again reaches the 12-mile arc in the south.
To the west, a portion of the arc extends past the easternmost edge of Maryland. The remaining western border runs east of due south from its intersection with the arc; the Wedge of land between the northwest part of the arc and the Maryland border was claimed by both Delaware and Pennsylvania until 1921, when Delaware's claim was confirmed. Delaware is with the lowest mean elevation of any state in the nation, its highest elevation, located at Ebright Azimuth, near Concord High School, is less than 450 feet above sea level. The northernmost part of the state is part of the Piedmont Plateau with rolling surfaces; the Atlantic Seaboard fall line follows the Robert Kirkwood Highway between Newark and Wilmington. A ridge about 75 to 80 feet in elevation extends along the western boundary of the state and separates the watersheds that feed Delaware River and Bay to the east and the Chesapeake Bay to the west. Since all of Delaware is a part of the Atlantic coastal plain, the effects of the ocean moderate its climate.
The state lies in the humid subtropical climate zone. Despite its small size, there is significant variation in mean temperature and amount of snowfall between Sussex County and New Castle County. Moderated by the Atlantic Ocean and Delaware Bay, the southern portion of the state has a milder climate and a longer growing season than the northern portion of the state. Delaware's all-time record high of 110 °F was recorded at Millsboro on July 21, 1930; the all-time record low of −17 °F was recorded at Millsboro on January 17, 1893. The transitional climate of Delaware supports a wide variety of vegetation. In the northern third of the state are found Northeastern coastal forests and mixed oak forests typical of the northeastern United States. In the southern two-thirds of the state are found Middle Atlantic coastal forests. Trap Pond State Park, along with areas in other parts of Sussex County, for example, support
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago, to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era; as with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when 60% of marine species were wiped out. A significant evolutionary milestone during the Silurian was the diversification of jawed fish and bony fish. Multi-cellular life began to appear on land in the form of small, bryophyte-like and vascular plants that grew beside lakes and coastlines, terrestrial arthropods are first found on land during the Silurian. However, terrestrial life would not diversify and affect the landscape until the Devonian; the Silurian system was first identified by British geologist Roderick Murchison, examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s.
He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, from the Latin name for Wales. This naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures. In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales, the germ of the modern geological time scale; as it was first identified, the "Silurian" series when traced farther afield came to overlap Sedgwick's "Cambrian" sequence, provoking furious disagreements that ended the friendship. Charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was "Gotlandian" after the strata of the Baltic island of Gotland; the French geologist Joachim Barrande, building on Murchison's work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge.
He divided the Silurian rocks of Bohemia into eight stages. His interpretation was questioned in 1854 by Edward Forbes, the stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils; the Llandovery Epoch lasted from 443.8 ± 1.5 to 433.4 ± 2.8 mya, is subdivided into three stages: the Rhuddanian, lasting until 440.8 million years ago, the Aeronian, lasting to 438.5 million years ago, the Telychian. The epoch is named for the town of Llandovery in Wales; the Wenlock, which lasted from 433.4 ± 1.5 to 427.4 ± 2.8 mya, is subdivided into the Sheinwoodian and Homerian ages. It is named after Wenlock Edge in England. During the Wenlock, the oldest-known tracheophytes of the genus Cooksonia, appear; the complexity of later Gondwana plants like Baragwanathia, which resembled a modern clubmoss, indicates a much longer history for vascular plants, extending into the early Silurian or Ordovician.
The first terrestrial animals appear in the Wenlock, represented by air-breathing millipedes from Scotland. The Ludlow, lasting from 427.4 ± 1.5 to 423 ± 2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, the Ludfordian stage. It is named for the town of Ludlow in England; the Přídolí, lasting from 423 ± 1.5 to 419.2 ± 2.8 mya, is the final and shortest epoch of the Silurian. It is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a cadastral field area. In North America a different suite of regional stages is sometimes used: Cayugan Lockportian Tonawandan Ontarian Alexandrian In Estonia the following suite of regional stages is used: Ohessaare stage Kaugatuma stage Kuressaare stage Paadla stage Rootsiküla stage Jaagarahu stage Jaani stage Adavere stage Raikküla stage Juuru stage With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe.
The high sea levels of the Silurian and the flat land resulted in a number of island chains, thus a rich diversity of environmental settings. During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late-Ordovician glaciation; the southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity; the continents of Avalonia and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. When the proto-Europe coll
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
Ecology is the branch of biology which studies the interactions among organisms and their environment. Objects of study include interactions of organisms that include biotic and abiotic components of their environment. Topics of interest include the biodiversity, distribution and populations of organisms, as well as cooperation and competition within and between species. Ecosystems are dynamically interacting systems of organisms, the communities they make up, the non-living components of their environment. Ecosystem processes, such as primary production, nutrient cycling, niche construction, regulate the flux of energy and matter through an environment; these processes are sustained by organisms with specific life history traits. Biodiversity means the varieties of species and ecosystems, enhances certain ecosystem services. Ecology is not synonymous with natural history, or environmental science, it overlaps with the related sciences of evolutionary biology and ethology. An important focus for ecologists is to improve the understanding of how biodiversity affects ecological function.
Ecologists seek to explain: Life processes and adaptations The movement of materials and energy through living communities The successional development of ecosystems The abundance and distribution of organisms and biodiversity in the context of the environment. Ecology has practical applications in conservation biology, wetland management, natural resource management, city planning, community health, economics and applied science, human social interaction. For example, the Circles of Sustainability approach treats ecology as more than the environment'out there', it is not treated as separate from humans. Organisms and resources compose ecosystems which, in turn, maintain biophysical feedback mechanisms that moderate processes acting on living and non-living components of the planet. Ecosystems sustain life-supporting functions and produce natural capital like biomass production, the regulation of climate, global biogeochemical cycles, water filtration, soil formation, erosion control, flood protection, many other natural features of scientific, economic, or intrinsic value.
The word "ecology" was coined in 1866 by the German scientist Ernst Haeckel. Ecological thought is derivative of established currents in philosophy from ethics and politics. Ancient Greek philosophers such as Hippocrates and Aristotle laid the foundations of ecology in their studies on natural history. Modern ecology became a much more rigorous science in the late 19th century. Evolutionary concepts relating to adaptation and natural selection became the cornerstones of modern ecological theory; the scope of ecology contains a wide array of interacting levels of organization spanning micro-level to a planetary scale phenomena. Ecosystems, for example, contain interacting life forms. Ecosystems are dynamic, they do not always follow a linear successional path, but they are always changing and sometimes so that it can take thousands of years for ecological processes to bring about certain successional stages of a forest. An ecosystem's area can vary from tiny to vast. A single tree is of little consequence to the classification of a forest ecosystem, but critically relevant to organisms living in and on it.
Several generations of an aphid population can exist over the lifespan of a single leaf. Each of those aphids, in turn, support diverse bacterial communities; the nature of connections in ecological communities cannot be explained by knowing the details of each species in isolation, because the emergent pattern is neither revealed nor predicted until the ecosystem is studied as an integrated whole. Some ecological principles, however, do exhibit collective properties where the sum of the components explain the properties of the whole, such as birth rates of a population being equal to the sum of individual births over a designated time frame; the main subdisciplines of ecology, population ecology and ecosystem ecology, exhibit a difference not only of scale, but of two contrasting paradigms in the field. The former focus on organisms distribution and abundance, while the focus on materials and energy fluxes; the scale of ecological dynamics can operate like a closed system, such as aphids migrating on a single tree, while at the same time remain open with regard to broader scale influences, such as atmosphere or climate.
Hence, ecologists classify ecosystems hierarchically by analyzing data collected from finer scale units, such as vegetation associations and soil types, integrate this information to identify emergent patterns of uniform organization and processes that operate on local to regional and chronological scales. To structure the study of ecology into a conceptually manageable framework, the biological world is organized into a nested hierarchy, ranging in scale from genes, to cells, to tissues, to organs, to organisms, to species, to populations, to communities, to ecosystems, to biomes, up to the level of the biosphere; this framework exhibits non-linear behaviors.
Taxus is a small genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are slow-growing and can be long-lived, reach heights of 2.5–20 metres, with trunk girth averaging 5 metres. They have reddish bark, flat, dark-green leaves 10–40 millimetres long and 2–3 mm broad, arranged spirally on the stem, but with the leaf bases twisted to align the leaves in two flat rows either side of the stem; the seed cones are modified, each cone containing a single seed 4–7 mm long surrounded by a modified scale which develops into a soft, bright red berry-like structure called an aril, 8–15 mm long and wide and open at the end. The arils are mature 6–9 months after pollination, with the seed contained are eaten by thrushes and other birds, which disperse the hard seeds undamaged in their droppings; the male cones are globose, 3–6 mm across, shed their pollen in early spring. Yews are dioecious, but occasional individuals can be variably monoecious, or change sex with time. All of the yews are closely related to each other, some botanists treat them all as subspecies or varieties of just one widespread species.
Other sources, recognize 9 species, for example the Plant List. The most distinct is the Sumatran yew, distinguished by its sparse, sickle-shaped yellow-green leaves; the Mexican yew is relatively distinct with foliage intermediate between Sumatran yew and the other species. The Florida yew, Mexican yew and Pacific yew are all rare species listed as threatened or endangered. All species of yew contain poisonous taxine alkaloids, with some variation in the exact formula of the alkaloid between the species. All parts of the tree except the arils contain the alkaloid; the arils are edible and sweet. This can have fatal results. Grazing animals cattle and horses, are sometimes found dead near yew trees after eating the leaves, though deer are able to break down the poisons and will eat yew foliage freely. In the wild, deer browsing of yews is so extensive that wild yew trees are restricted to cliffs and other steep slopes inaccessible to deer; the foliage is eaten by the larvae of some Lepidopteran insects including the moth willow beauty.
All parts of a yew plant are toxic to humans with the exception of the yew berries. These pollen granules are small, can pass through window screens. Male yews release abundant amounts of pollen in the spring. Yews in this genus are separate-sexed, males are allergenic, with an OPALS allergy scale rating of 10 out of 10. Female yews have an OPALS rating of 1, are considered "allergy-fighting". Yew wood is reddish brown, is springy, it was traditionally used to make bows the longbow. Latin taxus "yew tree," is borrowed, via Greek, from Taxša, the Scythian word for yew. British yews tend to be too gnarly, thus the wood for English longbows used at the Battle of Agincourt was imported from Spain or northern Italy. Ötzi, the Chalcolithic mummy found in 1991 in the Italian Alps, carried an unfinished bow made of yew wood. It is not surprising that in Norse mythology, the abode of the god of the bow, had the name Ydalir. Most longbow wood used in northern Europe was imported from Iberia, where climatic conditions are better for growing the knot-free yew wood required.
The yew longbow was the critical weapon used by the English in the defeat of the French cavalry at the Battle of Agincourt, 1415. It is suggested that English parishes were required to grow yews and, because of the trees' toxic properties, they were grown in the only enclosed area of a village – the churchyard; the yew tree can be found in church graveyards and is symbolic of sadness. Such a representation appears in Lord Alfred Tennyson's poem "In Memoriam A. H. H.". The yew can be long-lived; the Fortingall Yew has been considered to be the oldest tree in Europe, at something over 2,000 years old. Tradition has it that Pontius Pilate slept under it while on duty before 30 AD; this has been topped by a tree in the churchyard of a small Welsh village called St Cynog. It has been dated to 5,000 years old by dendrologist Janis Fry; such old trees consist of a circular ring of growths of yew, since their heart has long since rotted away. The Eihwaz rune is named after the yew, sometimes associated with the "evergreen" world tree, Yggdrasil.
Yews are used in landscaping and ornamental horticulture. Over 400 cultivars of yews have been named, the vast majority of these being derived from European yew or Japanese yew; the hybrid between these two species is Taxus media"Taxus" ×"media". A popular fastigiate selection of the European yew (Taxus baccata'
The Pinophyta known as Coniferophyta or Coniferae, or as conifers, are a division of vascular land plants containing a single extant class, Pinopsida. They are gymnosperms, cone-bearing seed plants. All extant conifers are perennial woody plants with secondary growth; the great majority are trees. Examples include cedars, Douglas firs, firs, kauri, pines, redwoods and yews; as of 1998, the division Pinophyta was estimated to contain eight families, 68 genera, 629 living species. Although the total number of species is small, conifers are ecologically important, they are the dominant plants over large areas of land, most notably the taiga of the Northern Hemisphere, but in similar cool climates in mountains further south. Boreal conifers have many wintertime adaptations; the narrow conical shape of northern conifers, their downward-drooping limbs, help them shed snow. Many of them seasonally alter their biochemistry to make them more resistant to freezing. While tropical rainforests have more biodiversity and turnover, the immense conifer forests of the world represent the largest terrestrial carbon sink.
Conifers are of great economic value for softwood paper production. The earliest conifers in the fossil record date to the late Carboniferous period arising from Cordaites, a genus of seed-bearing Gondwanan plants with cone-like fertile structures. Pinophytes and Ginkgophytes all developed at this time. An important adaptation of these gymnosperms was allowing plants to live without being so dependent on water. Other adaptations are pollen and the seed, which allows the embryo to be transported and developed elsewhere. Conifers appear to be one of the taxa that benefited from the Permian–Triassic extinction event, were the dominant land plants of the Mesozoic, they were overtaken by the flowering plants, which first appeared in the Cretaceous, became dominant in the Cenozoic era. They were the main food of herbivorous dinosaurs, their resins and poisons would have given protection against herbivores. Reproductive features of modern conifers had evolved by the end of the Mesozoic era. Conifer is a Latin word, a compound of conus and ferre, meaning "the one that bears cone".
The division name Pinophyta conforms to the rules of the International Code of Nomenclature for algae and plants, which state that the names of higher taxa in plants are either formed from the name of an included family, in this case Pinaceae, or are descriptive. A descriptive name in widespread use for the conifers is Coniferae. According to the ICN, it is possible to use a name formed by replacing the termination -aceae in the name of an included family, in this case preferably Pinaceae, by the appropriate termination, in the case of this division ‑ophyta. Alternatively, "descriptive botanical names" may be used at any rank above family. Both are allowed; this means that if conifers are considered a division, they may be called Coniferae. As a class they may be called Coniferae; as an order they may be called Coniferae or Coniferales. Conifers are the largest and economically most important component group of the gymnosperms, but they comprise only one of the four groups; the division Pinophyta consists of just one class, which includes both living and fossil taxa.
Subdivision of the living conifers into two or more orders has been proposed from time to time. The most seen in the past was a split into two orders and Pinales, but recent research into DNA sequences suggests that this interpretation leaves the Pinales without Taxales as paraphyletic, the latter order is no longer considered distinct. A more accurate subdivision would be to split the class into three orders, Pinales containing only Pinaceae, Araucariales containing Araucariaceae and Podocarpaceae, Cupressales containing the remaining families, but there has not been any significant support for such a split, with the majority of opinion preferring retention of all the families within a single order Pinales, despite their antiquity and diverse morphology; the conifers are now accepted as comprising seven families, with a total of 65–70 genera and 600–630 species. The seven most distinct families are linked in the box above right and phylogenetic diagram left. In other interpretations, the Cephalotaxaceae may be better included within the Taxaceae, some authors additionally recognize Phyllocladaceae as distinct from Podocarpaceae.
The family Taxodiaceae is here included in family Cupressaceae, but was recognized in the past and can still be found in many field guides. A new classification and linear sequence based on molecular data can be found in an article by Christenhusz et al; the conifers are an ancient group, with a fossil record extending back about 300 million years to the Paleozoic in the late Carboniferous period. Other classes and orders, now long extinct occur as fossils from the late Paleozoic and Mesozoic eras. Fossil conifers included many diverse forms, the most distinct from modern conifers being some herbaceous conifers with no woody stems. Major fossil orders of conifers or conifer-like plants include the Cordaitales, Vojnovskyales and also the Czekanowskiales (possibly