In biology, phylogenetics is the study of the evolutionary history and relationships among individuals or groups of organisms. These relationships are discovered through phylogenetic inference methods that evaluate observed heritable traits, such as DNA sequences or morphology under a model of evolution of these traits; the result of these analyses is a phylogeny – a diagrammatic hypothesis about the history of the evolutionary relationships of a group of organisms. The tips of a phylogenetic tree can be living organisms or fossils, represent the "end", or the present, in an evolutionary lineage. Phylogenetic analyses have become central to understanding biodiversity, evolution and genomes. Taxonomy is the identification and classification of organisms, it is richly informed by phylogenetics, but remains a methodologically and logically distinct discipline. The degree to which taxonomies depend on phylogenies differs depending on the school of taxonomy: phenetics ignores phylogeny altogether, trying to represent the similarity between organisms instead.
Usual methods of phylogenetic inference involve computational approaches implementing the optimality criteria and methods of parsimony, maximum likelihood, MCMC-based Bayesian inference. All these depend upon an implicit or explicit mathematical model describing the evolution of characters observed. Phenetics, popular in the mid-20th century but now obsolete, used distance matrix-based methods to construct trees based on overall similarity in morphology or other observable traits, assumed to approximate phylogenetic relationships. Prior to 1950, phylogenetic inferences were presented as narrative scenarios; such methods are ambiguous and lack explicit criteria for evaluating alternative hypotheses. The term "phylogeny" derives from the German Phylogenie, introduced by Haeckel in 1866, the Darwinian approach to classification became known as the "phyletic" approach. During the late 19th century, Ernst Haeckel's recapitulation theory, or "biogenetic fundamental law", was accepted, it was expressed as "ontogeny recapitulates phylogeny", i.e. the development of a single organism during its lifetime, from germ to adult, successively mirrors the adult stages of successive ancestors of the species to which it belongs.
But this theory has long been rejected. Instead, ontogeny evolves – the phylogenetic history of a species cannot be read directly from its ontogeny, as Haeckel thought would be possible, but characters from ontogeny can be used as data for phylogenetic analyses. 14th century, lex parsimoniae, William of Ockam, English philosopher and Franciscan friar, but the idea goes back to Aristotle, precursor concept 1763, Bayesian probability, Rev. Thomas Bayes, precursor concept 18th century, Pierre Simon first to use ML, precursor concept 1809, evolutionary theory, Philosophie Zoologique, Jean-Baptiste de Lamarck, precursor concept, foreshadowed in the 17th century and 18th century by Voltaire and Leibniz, with Leibniz proposing evolutionary changes to account for observed gaps suggesting that many species had become extinct, others transformed, different species that share common traits may have at one time been a single race foreshadowed by some early Greek philosophers such as Anaximander in the 6th century BC and the atomists of the 5th century BC, who proposed rudimentary theories of evolution 1837, Darwin's notebooks show an evolutionary tree 1843, distinction between homology and analogy, Richard Owen, precursor concept 1858, Paleontologist Heinrich Georg Bronn published a hypothetical tree to illustrating the paleontological "arrival" of new, similar species following the extinction of an older species.
Bronn did not propose a mechanism responsible for precursor concept. 1858, elaboration of evolutionary theory and Wallace in Origin of Species by Darwin the following year, precursor concept 1866, Ernst Haeckel, first publishes his phylogeny-based evolutionary tree, precursor concept 1893, Dollo's Law of Character State Irreversibility, precursor concept 1912, ML recommended and popularized by Ronald Fisher, precursor concept 1921, Tillyard uses term "phylogenetic" and distinguishes between archaic and specialized characters in his classification system 1940, term "clade" coined by Lucien Cuénot 1949, Jackknife resampling, Maurice Quenouille, precursor concept 1950, Willi Hennig's classic formalization 1952, William Wagner's groundplan divergence method 1953, "cladogenesis" coined 1960, "cladistic" coined by Cain and Harrison 1963, first attempt to use ML for phylogenetics and Cavalli-Sforza 1965 Camin-Sokal parsimony, first parsimony criterion and first computer program/algorithm for cladistic analysis both by Camin and Sokal character compatibility method called clique analysis, introduced independently by Camin and Sokal and E. O. Wilson 1966 English translation of Hennig "cladistics" and "cladogram" coined 1969 dynamic and successive wei
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
A barnacle is a type of arthropod constituting the infraclass Cirripedia in the subphylum Crustacea, is hence related to crabs and lobsters. Barnacles are marine, tend to live in shallow and tidal waters in erosive settings, they are sessile suspension feeders, have two nektonic larval stages. Around 1,220 barnacle species are known; the name "Cirripedia" is Latin, meaning "curl-footed". The study of barnacles is called cirripedology. Barnacles are encrusters; the most common, "acorn barnacles", are sessile. The order Pedunculata attach themselves by means of a stalk. Free-living barnacles are attached to the substratum by cement glands that form the base of the first pair of antennae. In some barnacles, the cement glands are fixed to a long, muscular stalk, but in most they are part of a flat membrane or calcified plate. A ring of plates surrounds the body, homologous with the carapace of other crustaceans; these consist of the rostrum, two lateral plates, two carinolaterals, a carina. In sessile barnacles, the apex of the ring of plates is covered by an operculum, which may be recessed into the carapace.
The plates are held together by various means, depending on species, in some cases being solidly fused. Inside the carapace, the animal lies with its limbs projecting upwards. Segmentation is indistinct, the body is more or less evenly divided between the head and thorax, with little, if any, abdomen. Adult barnacles have few appendages on their heads, with only a single, vestigial pair of antennae, attached to the cement gland; the six pairs of thoracic limbs are referred to as "cirri", which are feathery and long, being used to filter food, such as plankton, from the water and move it towards the mouth. Barnacles have no true heart, although a sinus close to the esophagus performs a similar function, with blood being pumped through it by a series of muscles; the blood vascular system is minimal. They have no gills, absorbing oxygen from the water through their limbs and the inner membrane of their carapaces; the excretory organs of barnacles are maxillary glands. The main sense of barnacles appears to be touch, with the hairs on the limbs being sensitive.
The adult has three photoreceptors, one median and two lateral. These photoreceptors record the stimulus for the barnacle shadow reflex, where a sudden decrease in light causes cessation of the fishing rhythm and closing of the opercular plates; the photoreceptors are only capable of sensing the difference between light and dark. This eye is derived from the primary naupliar eye. Barnacles have two distinct larval stages, the nauplius and the cyprid, before developing into a mature adult. A fertilised egg hatches into a nauplius: a one-eyed larva comprising a head and a telson, without a thorax or abdomen; this undergoes six moults, passing through five instars, before transforming into the cyprid stage. Nauplii are initially brooded by the parent, released after the first moult as larvae that swim using setae; the cyprid larva is the last larval stage before adulthood. It is not a feeding stage; the cyprid stage lasts from days to weeks. It explores potential surfaces with modified antennules. Larvae assess surfaces based upon their surface texture, relative wettability and the presence or absence and composition of a surface biofilm.
As the larva exhausts its finite energy reserves, it becomes less selective in the sites. It cements itself permanently to the substrate with another proteinaceous compound, undergoes metamorphosis into a juvenile barnacle. Typical acorn barnacles develop six hard calcareous plates to protect their bodies. For the rest of their lives, they are cemented to the substrate, using their feathery legs to capture plankton. Once metamorphosis is over and they have reached their adult form, barnacles continue to grow by adding new material to their calcified plates; these plates are not moulted. Most barnacles are hermaphroditic, although a few species are androdioecious; the ovaries are located in the base or stalk, may extend into the mantle, while the testes are towards the back of the head extending into the thorax. Moulted hermaphroditic individuals are receptive as females. Self-fertilization, although theoretically possible, has been experimentally shown to be rare in barnacles; the sessile lifestyle of barnacles makes sexual reproduction difficult, as the organisms cannot leave their shells to mate.
To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long penises. Barnacles have the largest penis to body size ratio of the animal kingdom. Barnacles can reproduce through a method called spermcasting, in which the male barnacle releases his sperm into the water and females pick it up and fertilise their eggs; the Rhizocephala superorder used to be considered hermaphroditic, but it turned out that its males inject themselves into the female's body, degrading to the condition of nothing more than sperm-producing cells. Most barnacles are suspension feeders.
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
Ernst Heinrich Philipp August Haeckel was a German zoologist, philosopher, professor, marine biologist, artist who discovered and named thousands of new species, mapped a genealogical tree relating all life forms, coined many terms in biology, including ecology, phylum and Protista. Haeckel promoted and popularised Charles Darwin's work in Germany and developed the influential but no longer held recapitulation theory claiming that an individual organism's biological development, or ontogeny and summarises its species' evolutionary development, or phylogeny; the published artwork of Haeckel includes over 100 detailed, multi-colour illustrations of animals and sea creatures, collected in his Kunstformen der Natur. As a philosopher, Ernst Haeckel wrote Die Welträthsel, the genesis for the term "world riddle". Ernst Haeckel was born on 16 February 1834, in Potsdam. In 1852 Haeckel completed studies at the cathedral high-school of Merseburg, he studied medicine in Berlin and Würzburg with Albert von Kölliker, Franz Leydig, Rudolf Virchow, with the anatomist-physiologist Johannes Peter Müller.
Together with Hermann Steudner he attended. In 1857 Haeckel attained a doctorate in medicine, afterwards he received the license to practice medicine; the occupation of physician appeared less worthwhile to Haeckel after contact with suffering patients. Haeckel studied under Karl Gegenbaur at the University of Jena for three years, earning a habilitation in comparative anatomy in 1861, before becoming a professor of zoology at Jena, where he remained for 47 years, from 1862 to 1909. Between 1859 and 1866 Haeckel worked on many phyla, such as radiolarians and annelids. During a trip to the Mediterranean, Haeckel named nearly 150 new species of radiolarians. From 1866 to 1867 Haeckel made an extended journey to the Canary Islands with Hermann Fol. During this period, he met with Thomas Huxley and Charles Lyell. In 1867 he married Agnes Huschke, their son Walter was born in 1868, their daughters Elizabeth in 1871 and Emma in 1873. In 1869 he traveled as a researcher to Norway, in 1871 to Croatia, in 1873 to Egypt and Greece.
In 1907 he had a museum built in Jena to teach the public about evolution. Haeckel retired from teaching in 1909, in 1910 he withdrew from the Evangelical Church of Prussia. On the occasion of his 80th birthday-celebration he was presented with a two-volume work entitled Was wir Ernst Haeckel verdanken, edited at the request of the German Monistenbund by Heinrich Schmidt of Jena. Haeckel's wife, died in 1915, he became frailer, breaking his leg and arm, he sold his "Villa Medusa" in Jena in 1918 to the Carl Zeiss foundation, which preserved his library. Haeckel died on 9 August 1919. Haeckel became the most famous proponent of Monism in Germany. Haeckel's affinity for the German Romantic movement, coupled with his acceptance of a form of Lamarckism, influenced his political beliefs. Rather than being a strict Darwinian, Haeckel believed that the characteristics of an organism were acquired through interactions with the environment and that ontogeny reflected phylogeny, he saw the social sciences as instances of "applied biology", that phrase was picked up and used for Nazi propaganda.
In 1906 Haeckel founded a group called the Monist League to promote his religious and political beliefs. This group lasted until 1933 and included such notable members as Wilhelm Ostwald, Georg von Arco, Helene Stöcker and Walter Arthur Berendsohn, he was the first person to use the term "first world war". Haeckel was a zoologist, an accomplished artist and illustrator, a professor of comparative anatomy. Although Haeckel's ideas are important to the history of evolutionary theory, although he was a competent invertebrate anatomist most famous for his work on radiolaria, many speculative concepts that he championed are now considered incorrect. For example, Haeckel described and named hypothetical ancestral microorganisms that have never been found, he was one of the first to consider psychology as a branch of physiology. He proposed the kingdom Protista in 1866, his chief interests lay in evolution and life development processes in general, including development of nonrandom form, which culminated in the beautifully illustrated Kunstformen der Natur.
Haeckel did not support natural selection. Haeckel advanced a version of the earlier recapitulation theory set out by Étienne Serres in the 1820s and supported by followers of Étienne Geoffroy Saint-Hilaire including Robert Edmond Grant, it proposed a link between ontogeny and phylogeny, summed up by Haeckel in the phrase "ontogeny recapitulates phylogeny". His concept of recapitulation has been refuted in the form he gave it, in favour of the ideas first advanced by Karl Ernst von Baer; the strong recapitulation hypothesis views ontogeny as repeating forms of adult ancestors, while weak recapitulation means that what is repeated is the ancestral embryonic development process. Haeckel supported the theory with embryo drawings that ha
Jean Léopold Nicolas Frédéric, Baron Cuvier, known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in natural sciences research in the early 19th century and was instrumental in establishing the fields of comparative anatomy and paleontology through his work in comparing living animals with fossils. Cuvier's work is considered the foundation of vertebrate paleontology, he expanded Linnaean taxonomy by grouping classes into phyla and incorporating both fossils and living species into the classification. Cuvier is known for establishing extinction as a fact—at the time, extinction was considered by many of Cuvier's contemporaries to be controversial speculation. In his Essay on the Theory of the Earth Cuvier proposed that now-extinct species had been wiped out by periodic catastrophic flooding events. In this way, Cuvier became the most influential proponent of catastrophism in geology in the early 19th century.
His study of the strata of the Paris basin with Alexandre Brongniart established the basic principles of biostratigraphy. Among his other accomplishments, Cuvier established that elephant-like bones found in the USA belonged to an extinct animal he would name as a mastodon, that a large skeleton dug up in Paraguay was of Megatherium, a giant, prehistoric ground sloth, he named the pterosaur Pterodactylus, described the aquatic reptile Mosasaurus, was one of the first people to suggest the earth had been dominated by reptiles, rather than mammals, in prehistoric times. Cuvier is remembered for opposing theories of evolution, which at the time were proposed by Jean-Baptiste de Lamarck and Geoffroy Saint-Hilaire. Cuvier believed there was no evidence for evolution, but rather evidence for cyclical creations and destructions of life forms by global extinction events such as deluges. In 1830, Cuvier and Geoffroy engaged in a famous debate, said to exemplify the two major deviations in biological thinking at the time – whether animal structure was due to function or morphology.
Cuvier rejected Lamarck's thinking. His most famous work is Le Règne Animal. In 1819, he was created a peer for life in honor of his scientific contributions. Thereafter, he was known as Baron Cuvier, he died in Paris during an epidemic of cholera. Some of Cuvier's most influential followers were Louis Agassiz on the continent and in the United States, Richard Owen in Britain, his name is one of the 72 names inscribed on the Eiffel Tower. Cuvier was born in Montbéliard, where his Protestant ancestors had lived since the time of the Reformation, his mother was Anne Clémence Chatel. At the time, the town, annexed to France on 10 October 1793, belonged to the Duchy of Württemberg, his mother, much younger than his father, tutored him diligently throughout his early years, so he surpassed the other children at school. During his gymnasium years, he had little trouble acquiring Latin and Greek, was always at the head of his class in mathematics and geography. According to Lee, "The history of mankind was, from the earliest period of his life, a subject of the most indefatigable application.
At the age of 10, soon after entering the gymnasium, he encountered a copy of Conrad Gessner's Historiae Animalium, the work that first sparked his interest in natural history. He began frequent visits to the home of a relative, where he could borrow volumes of the Comte de Buffon's massive Histoire Naturelle. All of these he read and reread, retaining so much of the information, that by the age of 12, "he was as familiar with quadrupeds and birds as a first-rate naturalist." He remained at the gymnasium for four years. Cuvier spent an additional four years at the Caroline Academy in Stuttgart, where he excelled in all of his coursework. Although he knew no German on his arrival, after only nine months of study, he managed to win the school prize for that language. Cuvier's German education exposed him to the work of the geologist Abraham Gottlob Werner, whose Neptunism and emphasis on the importance of rigorous, direct observation of three-dimensional, structural relationships of rock formations to geological understanding provided models for Cuvier's scientific theories and methods.
Upon graduation, he had no money on. So in July 1788, he took a job at Fiquainville chateau in Normandy as tutor to the only son of the Comte d'Héricy, a Protestant noble. There, during the early 1790s, he began his comparisons of fossils with extant forms. Cuvier attended meetings held at the nearby town of Valmont for the discussion of agricultural topics. There, he became acquainted with Henri Alexandre Tessier, he had been a physician and well-known agronomist, who had fled the Terror in Paris. After hearing Tessier speak on agricultural matters, Cuvier recognized him as the author of certain articles on agriculture in the Encyclopédie Méthodique and addressed him as M. Tessier. Tessier replied in dismay, "I am known and lost."—"Lost!" Replied M. Cuvier, "no, they soon became intimate and Tessier introduced Cuvier to his colleagues in Paris—"I have just found a pearl in the dungh
Plants are multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. Plants were treated as one of two kingdoms including all living things that were not animals, all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes. By one definition, plants form the clade Viridiplantae, a group that includes the flowering plants and other gymnosperms and their allies, liverworts and the green algae, but excludes the red and brown algae. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria, their chloroplasts contain b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is common.
There are about 320 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants. Green plants provide a substantial proportion of the world's molecular oxygen and are the basis of most of Earth's ecosystems on land. Plants that produce grain and vegetables form humankind's basic foods, have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs; the scientific study of plants is known as a branch of biology. All living things were traditionally placed into one of two groups and animals; this classification may date from Aristotle, who made the distincton between plants, which do not move, animals, which are mobile to catch their food. Much when Linnaeus created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia and Animalia. Since it has become clear that the plant kingdom as defined included several unrelated groups, the fungi and several groups of algae were removed to new kingdoms.
However, these organisms are still considered plants in popular contexts. The term "plant" implies the possession of the following traits multicellularity, possession of cell walls containing cellulose and the ability to carry out photosynthesis with primary chloroplasts; when the name Plantae or plant is applied to a specific group of organisms or taxon, it refers to one of four concepts. From least to most inclusive, these four groupings are: Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships; these are not yet settled, but one accepted relationship between the three groups described above is shown below. Those which have been called "plants" are in bold; the way in which the groups of green algae are combined and named varies between authors. Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom.
The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, they are no longer classified as plants as defined here; the Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common, they undergo closed mitosis without centrioles, have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. Two additional groups, the Rhodophyta and Glaucophyta have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour.
These groups differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event; this is the broadest modern definition of the term'plant'. In contrast, most other algae not only have different pigments but have chloroplasts with three or four surrounding membranes, they are not close relatives of the Archaeplastida having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in the broadest modern definition of the plant kingdom, although they were in the past; the green plants or Viridiplantae were traditionally divided into the green algae (including