The flowering plants known as angiosperms, Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families 13,164 known genera and c. 369,000 known species. Like gymnosperms, angiosperms are seed-producing plants. However, they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, the production of fruits that contain the seeds. Etymologically, angiosperm means a plant; the term comes from the Greek words sperma. The ancestors of flowering plants diverged from gymnosperms in the Triassic Period, 245 to 202 million years ago, the first flowering plants are known from 160 mya, they diversified extensively during the Early Cretaceous, became widespread by 120 mya, replaced conifers as the dominant trees from 100 to 60 mya. Angiosperms differ from other seed plants in several ways, described in the table below; these distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans.
Angiosperm stems are made up of seven layers. The amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms; the vascular bundles of the stem are arranged such that the phloem form concentric rings. In the dicotyledons, the bundles in the young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles, a complete ring is formed, a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside; the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.
Among the monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They once formed the stem increases in diameter only in exceptional cases; the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, provide the most trustworthy external characteristics for establishing relationships among angiosperm species; the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally from the axil of a leaf; as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More the flower-bearing portion of the plant is distinguished from the foliage-bearing or vegetative portion, forms a more or less elaborate branch-system called an inflorescence. There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become pollen grains, are the "male" cells and are borne in the stamens.
The "female" cells called megaspores, which will divide to become the egg cell, are contained in the ovule and enclosed in the carpel. The flower may consist only of these parts, as in willow, where each flower comprises only a few stamens or two carpels. Other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators; the individual members of these surrounding structures are known as petals. The outer series is green and leaf-like, functions to protect the rest of the flower the bud; the inner series is, in general, white or brightly colored, is more delicate in structure. It functions to attract bird pollinators. Attraction is effected by color and nectar, which may be secreted in some part of the flower; the characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans. While the majority of flowers are perfect or hermaphrodite, flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization.
Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot transfer pollen to the pistil. Homomorphic flowers may employ a biochemical mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers; the botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon and σπέρμα, was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked; the term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any
Citrus taxonomy refers to the botanical classification of the species, varieties and graft hybrids within the genus Citrus and related genera, found in cultivation and in the wild. Citrus taxonomy is complex. Cultivated citrus are derived from various citrus species found in the wild; some are only selections of the original wild types, while others are hybrids between two or more ancestors. Citrus plants hybridize between species with different morphologies, similar-looking citrus fruits may have quite different ancestries; some differ only in disease resistance. Conversely, different-looking varieties may be nearly genetically identical, differ only by a bud mutation. Detailed genomic analysis of wild and domesticated citrus cultivars has suggested that the progenitor of modern citrus species expanded out of the Himalayan foothills in a rapid radiation that has produced at least 10 wild species in South and East Asia and Australia. Most commercial cultivars are the product of hybridization among these wild species, with most coming from crosses involving citrons and pomelos.
Many different phylogenies for the non-hybrid citrus have been proposed, the phylogeny based on their nuclear genome does not match that derived from their chloroplast DNA a consequence of the rapid initial divergence. Taxonomic terminology is not yet settled. Most hybrids express different ancestral traits when planted from seeds and can continue a stable lineage only through vegetative propagation; some hybrids do reproduce true to type via nucellar seeds in a process called apomixis. As such, many hybrid species represent the clonal progeny of a single original F1 cross, though others combine fruit with similar characteristics that have arisen from distinct crosses. All of the wild'pure' citrus species trace to a common ancestor that lived in the Himalayan foothills, where a late-Miocene citrus fossil, Citrus linczangensis, has been found. At that time, a lessening of the monsoons and resultant drier climate in the region allowed the citrus ancestor to expand across south and east Asia in a rapid genetic radiation.
After the plant crossed the Wallace line a second radiation took place in the early Pliocene to give rise to the Australian species. Most modern cultivars are hybrids derived from a small number of'pure' original species. Though hundreds of species names have been assigned, a recent genomic study by Wu, et al. identified just ten ancestral species of citrus among those studied. Of these, seven were native to Asia: pomelo, the'pure' mandarins, micranthas, the Ichang papeda, the mangshanyegan, the oval kumquat. In Australia three were identified: the desert lime, round lime and the finger lime. Many other cultivars identified as species were found to be related variants or hybrids of these species, though not all cultivars were evaluated. Interbreeding seems possible between all citrus plants, between citrus plants and some plants which may or may not be categorized as citrus; the ability of citrus hybrids to self-pollinate and to reproduce sexually helps create new varieties. The three predominant ancestral citrus taxa are citron and mandarin.
These taxa interbreed despite being quite genetically distinct, having arisen through allopatric speciation, with citrons evolving in northern Indochina, pomelos in the Malay Archipelago, mandarins in Vietnam, southern China, Japan. The hybrids of these taxa include familiar citrus fruits like oranges, lemons and some tangerines. Citrons have been hybridized with other citrus taxa, for example, crossed with micrantha to produce the Key lime. In many cases, these crops are propagated asexually, lose their characteristic traits if bred. However, some of these hybrids have interbred with one another and with the original taxa, making the citrus family tree a complicated network. Kumquats do not interbreed with core taxa due to different flowering times, but hybrids exist. Australian limes are native to Australia and Papua New Guinea, so they did not interbreed with the core taxa, but they have been crossbred with mandarins and calamondins by modern breeders. Humans have deliberately bred new citrus fruits by propagating seedlings of spontaneous crosses, creating or selecting mutations of hybrids, crossing different varieties.
Many citrus types were identified and named by individual taxonomists, resulting in a large number of identified species: 870 by a 1969 count. Some order was brought to citrus taxonomy by two unified classification schemes, those of Chōzaburō Tanaka and Walter Tennyson Swingle, that can be viewed as extreme alternative visions of the genus. Swingle's system divided the Citrinae subtribe into three groups, the'primitive citrus' distant relatives, the closer'near citrus' including citrus-related genera like Atalantia, the'true citrus', which included Poncirus, Fortunella, Eremocitrus and Clymenia, all but the first now viewed to fall within Citrus, his Citrus he subdivided into two subgenera: citrons, mandarins, oranges and lemons were placed in subgenus Eucitrus, while the hardy but slow-growing trees with unpalatable fruit
Botanical nomenclature is the formal, scientific naming of plants. It is distinct from taxonomy. Plant taxonomy is concerned with classifying plants; the starting point for modern botanical nomenclature is Linnaeus' Species Plantarum of 1753. Botanical nomenclature is governed by the International Code of Nomenclature for algae and plants, which replaces the International Code of Botanical Nomenclature. Fossil plants are covered by the code of nomenclature. Within the limits set by that code there is another set of rules, the International Code of Nomenclature for Cultivated Plants which applies to plant cultivars that have been deliberately altered or selected by humans. Botanical nomenclature has a long history, going back beyond the period when Latin was the scientific language throughout Europe, to Theophrastus and other Greek writers. Many of these works have come down to us in Latin translations; the principal Latin writer on botany was Pliny the Elder. From Mediaeval times, Latin became the universal scientific language in Europe.
Most written plant knowledge was the property of monks Benedictine, the purpose of those early herbals was medicinal rather than plant science per se. It would require the invention of the printing press to make such information more available. Leonhart Fuchs, a German physician and botanist is considered the originator of Latin names for the increasing number of plants known to science. For instance he coined the name Digitalis in his De Historia Stirpium Commentarii Insignes. A key event was Linnaeus’ adoption of binomial names for plant species in his Species Plantarum. In the nineteenth century it became clear that there was a need for rules to govern scientific nomenclature, initiatives were taken to refine the body of laws initiated by Linnaeus; these were published in successively more sophisticated editions. For plants, key dates are 1867 and 1906; the most recent is the Melbourne Code, adopted in 2011. Another development was the insight into the delimitation of the concept of'plant'. More and more groups of organisms are being recognised as being independent of plants.
The formal names of most of these organisms are governed by the today. Some protists that do not fit into either plant or animal categories are treated under either or both of the ICN and the ICZN. A separate Code was adopted to govern the nomenclature of Bacteria, the International Code of Nomenclature of Bacteria. Botanical nomenclature is linked to plant taxonomy, botanical nomenclature serves plant taxonomy, but botanical nomenclature is separate from plant taxonomy. Botanical nomenclature is the body of rules prescribing which name applies to that taxon and if a new name may be coined. Plant taxonomy is an empirical science, a science that determines what constitutes a particular taxon: e.g. "What plants belong to this species?" and "What species belong to this genus?". The definition of the limits of a taxon is called its'circumscription'. For a particular taxon, if two taxonomists agree on its circumscription and position there is only one name which can apply under the ICN. Where they differ in opinion on any of these issues and the same plant may be placed in taxa with different names.
As an example, consider Siehe's Glory-of-the-Snow, Chionodoxa siehei: Taxonomists can disagree as to whether two groups of plants are sufficiently distinct to be put into one species or not. Thus Chionodoxa siehei and Chionodoxa forbesii have been treated as a single species by some taxonomists or as two species by others. If treated as one species, the earlier published name must be used, so plants called Chionodoxa siehei become Chionodoxa forbesii. Taxonomists can disagree as to whether two genera are sufficiently distinct to be kept separate or not. While agreeing that the genus Chionodoxa is related to the genus Scilla the bulb specialist Brian Mathew considers that their differences warrant maintaining separate genera. Others disagree, would refer to Chionodoxa siehei as Scilla siehei; the earliest published genus name must be used. Taxonomists can disagree as to the limits of families; when the Angiosperm Phylogeny Group first published its classification of the flowering plants in 1998, Chionodoxa siehei would have been placed in the family Hyacinthaceae.
In the 2009 revision of their classification, the APG no longer recognize the Hyacinthaceae as a separate family, merging it into a enlarged family Asparagaceae. Thus Chionodoxa siehei moves from the Hyacinthaceae to the Asparagaceae. Taxonomists can disagree as to the rank of a taxon. Rather than allow the Hyacinthaceae to disappear altogether, Chase et al. suggested that it be treated as a subfamily within the Asparagaceae. The ICN requires family names to end with "-aceae" and subfamily names to end with "-oideae", thus a possible name for the Hyacinthaceae when treated as a subfamily would be'Hyacinthoideae'. However, the name Scilloideae had been published in 1835 as the name for a subfamily containing the genus Scilla, so this name has priority and must be used. Hence for those taxonomists who accept the APG system of 2009, Chionodoxa siehei can be placed in the subfamily Scil
Acacia sensu lato
Acacia s.l. known as mimosa, thorntree or wattle, is a polyphyletic genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae. It was described by the Swedish botanist Carl Linnaeus in 1773 based on the African species Acacia nilotica. Many non-Australian species tend to be thorny. All species are pod-bearing, with sap and leaves bearing large amounts of tannins and condensed tannins that found use as pharmaceuticals and preservatives; the genus Acacia constitutes, in its traditional circumspection, the second largest genus in Fabaceae, with 1,300 species, about 960 of them native to Australia, with the remainder spread around the tropical to warm-temperate regions of both hemispheres, including Europe, southern Asia, the Americas. The genus was divided into five separate genera under the tribe "Acacieae"; the genus now called Acacia represents the majority of the Australian species and a few native to southeast Asia, Réunion, Pacific Islands. Most of the species outside Australia, a small number of Australian species, are classified into Vachellia and Senegalia.
The two final genera and Mariosousa, each contain about a dozen species from the Americas. This article describes acacias in the broader sense. English botanist and gardener Philip Miller adopted the name Acacia in 1754; the generic name is derived from ἀκακία, the name given by early Greek botanist-physician Pedanius Dioscorides to the medicinal tree A. nilotica in his book Materia Medica. This name derives from the Ancient Greek word for its characteristic thorns, ἀκίς; the species name nilotica was given by Linnaeus from this tree's best-known range along the Nile river. This became the type species of the genus; the traditional circumscription of Acacia contained 1,300 species. However, evidence began to accumulate. Queensland botanist Les Pedley proposed the subgenus Phyllodineae be renamed Racosperma and published the binomial names; this was taken up in New Zealand but not followed in Australia, where botanists declared more study was needed. Consensus emerged that Acacia needed to be split as it was not monophyletic.
This led to Australian botanists Bruce Maslin and Tony Orchard pushing for the retypification of the genus with an Australian species instead of the original African type species, an exception to traditional rules of priority that required ratification by the International Botanical Congress. That decision has been controversial, debate continued, with some taxonomists deciding to continue to use the traditional Acacia sensu lato circumscription of the genus, in defiance of decisions by an International Botanical Congress. However, a second International Botanical Congress has now confirmed the decision to apply the name Acacia to the Australian plants, which some had been calling Racosperma, which had formed the overwhelming majority of Acacia sensu lato. Debate continues regarding the traditional acacias of Africa placed in Senegalia and Vachellia, some of the American species placed in Acaciella and Mariosousa. Acacias belong to the subfamily Mimosoideae, the major clades of which may have formed in response to drying trends and fire regimes that accompanied increased seasonality during the late Oligocene to early Miocene.
Pedley, following Vassal, viewed Acacia as comprising three large subgenera, but subsequently raised the rank of these groups to genera Acacia and Racosperma, underpinned by genetic studies. In common parlance, the term "acacia" is applied to species of the genus Robinia, which belongs in the pea family. Robinia pseudoacacia, an American species locally known as black locust, is sometimes called "false acacia" in cultivation in the United Kingdom and throughout Europe; the leaves of acacias are compound pinnate in general. In some species, more in the Australian and Pacific Islands species, the leaflets are suppressed, the leaf-stalks become vertically flattened in order to serve the purpose of leaves; these are known as "phyllodes". The vertical orientation of the phyllodes protects them from intense sunlight since with their edges towards the sky and earth they do not intercept light as as horizontally placed leaves. A few species lack leaves or phyllodes altogether but instead possess cladodes, modified leaf-like photosynthetic stems functioning as leaves.
The small flowers have five small petals hidden by the long stamens, are arranged in dense, globular or cylindrical clusters. Acacia flowers can be distinguished from those of a large related genus, Albizia, by their stamens, which are not joined at the base. Unlike individual Mimosa flowers, those of Acacia have more than ten stamens; the plants bear spines those species growing in arid regions. These sometimes represent branches that have become short and pungent, though they sometimes represent leaf-stipules. Acacia armata is the kangaroo-thorn of Australia, Acacia erioloba is the camelthorn of Africa. Acacia seeds can be difficult to germinate. Research has found that immersing the seeds in various temperatures
Flora is the plant life occurring in a particular region or time the occurring or indigenous—native plant life. The corresponding term for animal life is fauna. Flora and other forms of life such as fungi are collectively referred to as biota. Sometimes bacteria and fungi are referred to as flora, as in the terms gut flora or skin flora; the word "flora" comes from the Latin name of Flora, the goddess of plants and fertility in Roman mythology. The technical term "flora" is derived from a metonymy of this goddess at the end of the sixteenth century, it was first used in poetry to denote the natural vegetation of an area, but soon assumed the meaning of a work cataloguing such vegetation. Moreover, "Flora" was used to refer to the flowers of an artificial garden in the seventeenth century; the distinction between vegetation and flora was first made by Jules Thurmann. Prior to this, the two terms were used indiscriminately. Plants are grouped into floras based on region, special environment, or climate.
Regions can be distinct habitats like mountain vs. flatland. Floras can mean plant life of a historic era as in fossil flora. Lastly, floras may be subdivided by special environments: Native flora; the native and indigenous flora of an area. Agricultural and horticultural flora; the plants that are deliberately grown by humans. Weed flora. Traditionally this classification was applied to plants regarded as undesirable, studied in efforts to control or eradicate them. Today the designation is less used as a classification of plant life, since it includes three different types of plants: weedy species, invasive species, native and introduced non-weedy species that are agriculturally undesirable. Many native plants considered weeds have been shown to be beneficial or necessary to various ecosystems; the flora of a particular area or time period can be documented in a publication known as a "flora". Floras may require specialist botanical knowledge to use with any effectiveness. Traditionally they are books.
Simon Paulli's Flora Danica of 1648 is the first book titled "Flora" to refer to the plant world of a certain region. It describes medicinal plants growing in Denmark; the Flora Sinensis by the Polish Jesuit Michał Boym is another early example of a book titled "Flora". However, despite its title it covered not only plants, but some animals of the region, China and India. A published flora contains diagnostic keys; these are dichotomous keys, which require the user to examine a plant, decide which one of two alternatives given best applies to the plant. Biome — a major regional group of distinctive plant and animal communities Fauna Fauna and Flora Preservation Society Herbal Horticultural flora Megaflora Pharmacopoeia The Plant List Vegetation — a general term for the plant life of a regionCategoriesFlora by continent Flora by country Flora by region eFloras — a collection of on-line floras Chilebosque — checklist of Chilean native flora Flora of NW Europe with descriptions and a quiz to test your knowledge Flora of Australia Online Flora of New Zealand Series Online
Kudzu is a group of plants in the genus Pueraria, in the pea family Fabaceae, subfamily Faboideae. They are climbing and trailing perennial vines native to much of eastern Asia, Southeast Asia, some Pacific islands; the name is derived from the Japanese name for the plant East Asian arrowroot, クズ or 葛. Where these plants are naturalized, they are considered noxious weeds; the plant climbs over trees or shrubs and grows so that it kills them by heavy shading. The plant is edible, but sprayed with herbicides; the name kudzu describes one or more species in the genus Pueraria that are related, some of them are considered to be varieties rather than full species. The morphological differences between them are subtle, they are: P. montana P. edulis P. phaseoloides P. tuberosa Kudzu spreads by vegetative reproduction via stolons that root at the nodes to form new plants and by rhizomes. Kudzu spreads by seeds, which are contained in pods and mature in the autumn, although this is rare. One or two viable seeds are produced per cluster of pods.
The hard-coated seeds can remain viable for several years, can germinate only when soil is persistently soggy for 5-7 days, with temperatures above 20°C. Once germinated, saplings must be kept in a well-drained medium. During this stage of growth, kudzu must receive as much sunlight as possible. Kudzu saplings are sensitive to mechanical disturbance, are damaged by chemical fertilizers, they do not tolerate long periods of shade or high water tables. Kudzu has been used as a form of erosion control; as a legume, it increases the nitrogen in the soil by a symbiotic relationship with nitrogen-fixing bacteria. Its deep taproots transfer valuable minerals from the subsoil to the topsoil, thereby improving the topsoil. In the deforested section of the central Amazon Basin in Brazil, it has been used for improving the soil pore-space in clay latosols, thus freeing more water for plants than in the soil prior to deforestation. Kudzu can be used by grazing animals, as it is high in quality as a forage and palatable to livestock.
It can be grazed until frost and slightly after. Kudzu had been used in the southern United States to feed goats on land that had limited resources. Kudzu hay has a 15–18% crude protein content and over 60% total digestible nutrient value; the quality of the leaves decreases, however, as vine content increases relative to the leaf content. Kudzu has low forage yields despite its rate of growth, yielding around two to four tons of dry matter per acre annually, it is difficult to bale due to its vining growth and its slowness in shedding water. This makes it necessary to place kudzu hay under sheltered protection after being baled. Fresh kudzu is consumed by all types of grazing animals, but frequent grazing over three to four years can ruin established stands. Thus, kudzu only serves well as a grazing crop on a temporary basis. Kudzu fiber has long been used for fiber basketry; the long runners which propagate the kudzu fields and the larger vines which cover trees make excellent weaving material.
Some basketmakers use the material green. Others use it after splitting it in half, allowing it to dry and rehydrating it using hot water. Both traditional and contemporary basketry artists use kudzu. Kudzu contains isoflavones, including puerarin, daidzin and salvianolic acid, among numerous others identified. In traditional Chinese medicine, where it is known as gé gēn, kudzu is considered one of the 50 fundamental herbs thought to have therapeutic effects, although there is no high-quality clinical research to indicate it has any activity or therapeutic use in humans. Adverse effects may occur if kudzu is taken by people with hormone-sensitive cancer or those taking tamoxifen, antidiabetic medications, or methotrexate; the roots contain starch. In Vietnam, the starch called bột sắn dây is flavoured with pomelo oil and used as a drink in the summer. In Japan, the plant is known as the starch named kuzuko. Kuzuko is used in dishes including kuzumochi, mizu manjū, kuzuyu, it serves as a thickener for sauces, can substitute for cornstarch.
The flowers are used to make a jelly. Roots and leaves of kudzu show antioxidant activity that suggests food uses. Nearby bee colonies may forage on kudzu nectar during droughts as a last resort, producing a low-viscosity red or purple honey that tastes of grape jelly or bubblegum. Kudzu has been used for centuries in East Asia to make herbal teas and tinctures. Kudzu powder is used in Japan to make an herbal tea called kuzuyu. Kakkonto is a herbal drink with its origin in traditional Chinese medicine, it is made from a mixture of ginger, Chinese peony, jujube and powder ground from the root of the kudzu plant. As the name, which translates to "kudzu infusion", kudzu, or Pueraria lobata, serves as the main ingredient. Together these plants are used to create a drink containing puerarin, paenoflorin, cinnamic acid, glycyrrhizin and gingerol. Kudzu fiber, known as ko-hemp, is used traditionally to make clothing and paper, has been investigated for industrial-scale use, it may become a va
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