A genus (/ˈdʒiːnəs/, pl. genera /ˈdʒɛnərə/) is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses,[1] in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.

E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera. Panthera is a genus within the family Felidae.

The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however,[2][3] including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:

  1. monophyly – all descendants of an ancestral taxon are grouped together (i.e. phylogenetic analysis should clearly demonstrate both monophyly and validity as a separate lineage[4]).
  2. reasonable compactness – a genus should not be expanded needlessly; and
  3. distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; DNA sequences are a consequence rather than a condition of diverging evolutionary lineages except in cases where they directly inhibit gene flow (e.g. postzygotic barriers).

Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.[4]

The hierarchy of biological classification's eight major taxonomic ranks. A family contains one or more genera. Intermediate minor rankings are not shown.


The term "genus" comes from the Latin genus ("origin, type, group, race"),[5][6] a noun form cognate with gignere ("to bear; to give birth to"). Linnaeus popularized its use in his 1753 Species Plantarum, but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera".[7]


The scientific name (or the scientific epithet) of a genus is also called the generic name; it is always capitalised. It plays a fundamental role in binomial nomenclature, the system of naming organisms, where it is combined with the scientific name of a species: see Specific name (botany) and Specific name (zoology).

Use in nomenclature

The rules for the scientific names of organisms are laid down in the Nomenclature Codes, which allow each species a single unique name that, for "animals" (including protists), "plants" (also including algae and fungi) and prokaryotes (Bacteria and Archaea), is Latin and binomial in form; this contrasts with common or vernacular names, which are non-standardized, can be non-unique, and typically also vary by country and language of usage.

Except for viruses, the standard format for a species name comprises the generic name, indicating the genus to which the species belongs, followed by the specific epithet, which (within that genus) is unique to the species. For example, the gray wolf's scientific name is Canis lupus, with Canis (Lat. "dog") being the generic name shared by the wolf's close relatives and lupus (Lat. "wolf") being the specific name particular to the wolf. A botanical example would be Hibiscus arnottianus, a particular species of the genus Hibiscus native to Hawaii. The specific name is written in lower-case and may be followed by subspecies names in zoology or a variety of infraspecific names in botany.

When the generic name is already known from context, it may be shortened to its initial letter, for example C. lupus in place of Canis lupus. Where species are further subdivided, the generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example Canis lupus familiaris for the domestic dog (when considered a subspecies of the gray wolf) in zoology, or as a botanical example, Hibiscus arnottianus ssp. immaculatus. Also, as visible in the above examples, the Latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in italics.

The scientific names of virus species are descriptive, not binomial in form, and may or may not incorporate an indication of their containing genus; for example the virus species "Salmonid herpesvirus 1", "Salmonid herpesvirus 2" and "Salmonid herpesvirus 3" are all within the genus Salmonivirus, however the genus to which the species with the formal names "Everglades virus" and "Ross River virus" are assigned is Alphavirus.

As with scientific names at other ranks, in all groups other than viruses, names of genera may be cited with their authorities, typically in the form "author, year" in zoology, and "standard abbreviated author name" in botany. Thus in the examples above, the genus Canis would be cited in full as "Canis Linnaeus, 1758" (zoological usage), while Hibiscus, also first established by Linnaeus but in 1753, is simply "Hibiscus L." (botanical usage).

The type concept

Each genus should have a designated type, although in practice there is a backlog of older names without one. In zoology, this is the type species and the generic name is permanently associated with the type specimen of its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes a junior synonym and the remaining taxa in the former genus need to be reassessed.

Categories of generic name

In zoological usage, taxonomic names, including those of genera, are classified as "available" or "unavailable". Available names are those published in accordance with the International Code of Zoological Nomenclature and not otherwise suppressed by subsequent decisions of the International Commission on Zoological Nomenclature (ICZN); the earliest such name for any taxon (for example, a genus) should then be selected as the "valid" (i.e., current or accepted) name for the taxon in question.

Consequently, there will be more available names than valid names at any point in time, which names are currently in use depending on the judgement of taxonomists in either either combining taxa described under multiple names, or splitting taxa which may bring available names previously treated as synonyms back into use. "Unavailable" names in zoology comprise names that either were not published according to the provisions of the ICZN Code, or have subsequently been suppressed, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated.[8]

In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a validly published name. An invalidly published name is a nomen invalidum or nom. inval.; a rejected name is a nomen rejiciendum or nom. rej.; a later homonym of a validly published name is a nomen illegitimum or nom. illeg.; for a full list refer the International Code of Nomenclature for algae, fungi, and plants (ICNafp) and the work cited above by Hawksworth, 2010.[8] In place of the "valid taxon" in zoology, the nearest equivalent in botany is "correct name" or "current name" which can, again, differ or change with alternative taxonomic treatments or new information that results in previously accepted genera being combined or split.

Prokaryote and virus Codes of Nomenclature also exist which serve as a reference for designating currently accepted genus names as opposed to others which may be either reduced to synonymy, or, in the case of prokaryotes, relegated to a status of "names without standing in prokaryotic nomenclature".

An available (zoological) or validly published (botanical) name that has been historically applied to a genus but is not regarded as the accepted (current/valid) name for the taxon is termed a synonym; some authors also include unavailable names in lists of synonyms as well as available names, such as misspellings, names previously published without fulfilling all of the requirements of the relevant nomenclatural Code, and rejected or suppressed names.

A particular genus name may have zero to many synonyms, the latter case generally if the genus has been known for a long time and redescribed as new by a range of subsequent workers, or if a range of genera previously considered separate taxa have subsequently been consolidated into one. For example, the World Register of Marine Species presently lists 8 genus-level synonyms for the sperm whale genus Physeter Linnaeus, 1758,[9] and 13 for the bivalve genus Pecten O.F. Müller, 1776.[10]

Identical names (homonyms)

Within the same kingdom, one generic name can apply to one genus only. However, many names have been assigned (usually unintentionally) to two or more different genera. For example, the platypus belongs to the genus Ornithorhynchus although George Shaw named it Platypus in 1799 (these two names are thus synonyms). However, the name Platypus had already been given to a group of ambrosia beetles by Johann Friedrich Wilhelm Herbst in 1793. A name that means two different things is a homonym. Since beetles and platypuses are both members of the kingdom Animalia, the name could not be used for both. Johann Friedrich Blumenbach published the replacement name Ornithorhynchus in 1800.

However, a genus in one kingdom is allowed to bear a scientific name that is in use as a generic name (or the name of a taxon in another rank) in a kingdom that is governed by a different nomenclature code. Names with the same form but applying to different taxa are called "homonyms". Although this is discouraged by both the International Code of Zoological Nomenclature and the International Code of Nomenclature for algae, fungi, and plants, there are some five thousand such names in use in more than one kingdom. For instance,

A list of generic homonyms (with their authorities), including both available (validly published) and selected unavailable names, has been compiled by the Interim Register of Marine and Nonmarine Genera (IRMNG).[11]

Use in higher classifications

The type genus forms the base for higher taxonomic ranks, such as the family name Canidae ("Canids") based on Canis. However, this does not typically ascend more than one or two levels: the order to which dogs and wolves belong is Carnivora ("Carnivores").

Numbers of accepted genera

The numbers of either accepted, or all published genus names is not known precisely although the latter value has been estimated by Rees et al., 2017[12] at approximately 510,000 as at end 2016, increasing at some 2,500 per year. "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses[1] and prokaryotes,[13] while for others there are compendia with no "official" standing such as Index Fungorum for Fungi,[14] Index Nominum Algarum[15] and AlgaeBase[16] for algae, Index Nominum Genericorum[17] and the International Plant Names Index[18] for plants in general, and ferns through angiosperms, respectively, and Nomenclator Zoologicus[19] and the Index to Organism Names[20] for zoological names.

A deduplicated list of genus names covering all taxonomic groups, compiled from resources such as the above as well as other literature sources, created as the "Interim Register of Marine and Nonmarine Genera" (IRMNG), is estimated to contain around 95% of all published names at generic level, and lists approximately 490,100 genus names in its March 2019 release;[11] of these, approx. 265,500 are presently flagged "accepted" (including both extant and fossil taxa), 127,500 as unaccepted for a range of reasons, and an additional 126,000 not yet assessed for taxonomic status. Included in the 265,500 accepted, extant plus fossil genus names in the March 2019 edition of IRMNG are 188,158 genera of animals (kingdom Animalia), 21,935 Plantae (land plants and non-Chromistan algae), 10,231 Fungi, 9,989 Chromista, 1,963 Protozoa, 3,387 Prokaryotes (3,247 Bacteria plus 140 Archaea) and 851 Viruses, although totals for some eukaryote groups will be an underestimate since the present "uncertain" (=unassessed) category (which contains largely animal and protozoan genus names) contains a mix of names that should ultimately be allocated either to "accepted" and "unaccepted" upon further investigation.

By comparison, the 2018 annual edition of the Catalogue of Life (estimated >90% complete, for extant species in the main) contains currently 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species,[21] also including genus names only (no species) for some groups.

Genus size

Number of reptile genera with a given number of species
Number of reptile genera with a given number of species. Most genera have only one or a few species but a few may have hundreds. Based on data from the Reptile Database (as of May 2015).

The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) reptiles, which have about 1180 genera, the most (>300) have only 1 species, ~360 have between 2 and 4 species, 260 have 5-10 species, ~200 have 11-50 species, and only 27 genera have more than 50 species (see figure).[22] However, some insect genera such as the bee genera Lasioglossum and Andrena have over 1000 species each. The largest flowering plant genus, Astragalus, contains over 3,000 species.[23]

Which species are assigned to a genus is somewhat arbitrary. Although all species within a genus are supposed to be "similar" there are no objective criteria for grouping species into genera. There is much debate among zoologists whether large, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance, the lizard genus Anolis has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets.[24]

See also


  1. ^ a b "ICTV Taxonomy". International Committee on Taxonomy of Viruses. 2017. Retrieved May 29, 2018.
  2. ^ Sigward, J. D.; Sutton, M. D.; Bennett, K. D. (2018). "How big is a genus? Towards a nomothetic systematics". Zoological Journal of the Linnean Society. 183 (2): 237–252. doi:10.1093/zoolinnean/zlx059.
  3. ^ Gill, F. B.; Slikas, B.; Sheldon, F. H. (2005). "Phylogeny of titmice (Paridae): II. Species relationships based on sequences of the mitochondrial cytochrome-b gene". Auk. 122 (1): 121–143. doi:10.1642/0004-8038(2005)122[0121:POTPIS]2.0.CO;2.
  4. ^ a b de la Maza-Benignos, Mauricio; Lozano-Vilano, Ma. de Lourdes; García-Ramírez, María Elena (December 2015). "Response paper: Morphometric article by Mejía et al. 2015 alluding genera Herichthys and Nosferatu displays serious inconsistencies". Neotropical Ichthyology. 13 (4): 673–676. doi:10.1590/1982-0224-20150066.
  5. ^ "Genus". Merriam-Webster Dictionary. Retrieved 2019-03-19.
  6. ^ Harper, Douglas. "genus". Online Etymology Dictionary.
  7. ^ Stuessy, T. F. (2009). Plant Taxonomy: The Systematic Evaluation of Comparative Data (2nd ed.). New York, New York, US: Columbia University Press. p. 42. ISBN 9780231147125.
  8. ^ a b D. L. Hawksworth (2010). Terms Used in Bionomenclature: The Naming of Organisms and Plant Communities : Including Terms Used in Botanical, Cultivated Plant, Phylogenetic, Phytosociological, Prokaryote (bacteriological), Virus, and Zoological Nomenclature. GBIF. pp. 1–215. ISBN 978-87-92020-09-3.
  9. ^ World Register of Marine Species: Physeter Linnaeus, 1758
  10. ^ World Register of Marine Species: Pecten O. F. Müller, 1776
  11. ^ a b "IRMNG: Interim Register of Marine and Nonmarine Genera". Retrieved 2016-11-17.
  12. ^ Rees, Tony; Vandepitte, Leen; Decock, Wim; Vanhoorne, Bart (2017). "IRMNG 2006–2016: 10 Years of a Global Taxonomic Database". Biodiversity Informatics. 12: 1–44. doi:10.17161/bi.v12i0.6522.
  13. ^ List of Prokaryotic names with Standing in Nomenclature
  14. ^ Index Fungorum
  15. ^ Index Nominum Algarum
  16. ^ AlgaeBase
  17. ^ Index Nominum Genericorum
  18. ^ The International Plant Names Index
  19. ^ Nomenclator Zoologicus
  20. ^ Index to Organism Names
  21. ^ Information: Catalogue of Life: 2018 Annual Checklist
  22. ^ The Reptile Database
  23. ^ Frodin, David G. (2004). "History and concepts of big plant genera". Taxon. 53 (3): 753–776. doi:10.2307/4135449. JSTOR 4135449.
  24. ^ Nicholson, K. E.; Crother, B. I.; Guyer, C.; Savage, J.M. (2012). "It is time for a new classification of anoles (Squamata: Dactyloidae)" (PDF). Zootaxa. 3477: 1–108.

External links


Anseriformes is an order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which includes over 170 species of waterfowl, among them the ducks, geese, and swans. Most modern species in the order are highly adapted for an aquatic existence at the water surface. With the exception of screamers, all have phalli, a trait that has been lost in the Neoaves. Due to their aquatic nature, most species are web-footed.


Australopithecus ( OS-trə-lo-PITH-i-kəs; from Latin australis, meaning 'southern', and Greek πίθηκος (pithekos), meaning 'ape', informal australopithecine or australopith (although the term australopithecine has a broader meaning as a member of the subtribe Australopithecina,  which includes this genus as well as the Paranthropus, Kenyanthropus, Ardipithecus, and Praeanthropus genera)  is a 'genus' of hominins.

From paleontological and archaeological evidence, the genus Australopithecus apparently evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct two million years ago. Australopithecus is not literally extinct (in the sense of having no living descendants) as the Kenyanthropus, Paranthropus and Homo genera probably emerged as sister of a late Australopithecus species such as A. Africanus and/or A. Sediba. During that time, a number of australopithecine species emerged, including Australopithecus afarensis, A. africanus, A. anamensis, A. bahrelghazali, A. deyiremeda (proposed), A. garhi, and A. sediba.

For some hominid species of this time – A. robustus, A. boisei and A. aethiopicus – some debate exists whether they truly constitute members of the genus Australopithecus. If so, they would be considered 'robust australopiths', while the others would be 'gracile australopiths'. However, if these more robust species do constitute their own genus, they would be under the genus name Paranthropus, a genus described by Robert Broom when the first discovery was made in 1938, which makes these species P. robustus, P. boisei and P. aethiopicus.

Australopithecus species played a significant part in human evolution, the genus Homo being derived from Australopithecus at some time after three million years ago.

In addition, they were the first hominids to possess certain genes, known as the duplicated SRGAP2, which increased the length and ability of neurons in the brain. One of the australopith species evolved into the genus Homo in Africa around two million years ago (e.g. Homo habilis), and eventually modern humans, H. sapiens sapiens.In January 2019, scientists reported that Australopithecus sediba is distinct from, but shares anatomical similarities to, both the older Australopithecus africanus, and the younger Homo habilis.

Binomial nomenclature

Binomial nomenclature ("two-term naming system"), also called binominal nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomial name (which may be shortened to just "binomial"), a binomen, binominal name or a scientific name; more informally it is also called a Latin name. The first part of the name – the generic name – identifies the genus to which the species belongs, while the second part – the specific name or specific epithet – identifies the species within the genus. For example, humans belong to the genus Homo and within this genus to the species Homo sapiens. Tyrannosaurus rex is probably the most widely known binomial. The formal introduction of this system of naming species is credited to Carl Linnaeus, effectively beginning with his work Species Plantarum in 1753. But Gaspard Bauhin, in as early as 1623, had introduced in his book Pinax theatri botanici (English, Illustrated exposition of plants) many names of genera that were later adopted by Linnaeus.The application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature (ICZN) for animals and the International Code of Nomenclature for algae, fungi, and plants (ICNafp). Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences, both in the terminology they use and in their precise rules.

In modern usage, the first letter of the first part of the name, the genus, is always capitalized in writing, while that of the second part is not, even when derived from a proper noun such as the name of a person or place. Similarly, both parts are italicized when a binomial name occurs in normal text (or underlined in handwriting). Thus the binomial name of the annual phlox (named after botanist Thomas Drummond) is now written as Phlox drummondii.

In scientific works, the authority for a binomial name is usually given, at least when it is first mentioned, and the date of publication may be specified.

In zoology

"Patella vulgata Linnaeus, 1758". The name "Linnaeus" tells the reader who it was that first published a description and name for this species of limpet; 1758 is the date of the publication in which the original description can be found (in this case the 10th edition of the book Systema Naturae).

"Passer domesticus (Linnaeus, 1758)". The original name given by Linnaeus was Fringilla domestica; the parentheses indicate that the species is now considered to belong in a different genus. The ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs usually include such information.

In botany

"Amaranthus retroflexus L." – "L." is the standard abbreviation used in botany for "Linnaeus".

"Hyacinthoides italica (L.) Rothm. – Linnaeus first named this bluebell species Scilla italica; Rothmaler transferred it to the genus Hyacinthoides; the ICNafp does not require that the dates of either publication be specified.


A booby is a seabird in the genus Sula, part of the Sulidae family. Boobies are closely related to the gannets (Morus), which were formerly included in Sula.

Botanical name

A botanical name is a formal scientific name conforming to the International Code of Nomenclature for algae, fungi, and plants (ICN) and, if it concerns a plant cultigen, the additional cultivar or Group epithets must conform to the International Code of Nomenclature for Cultivated Plants (ICNCP). The code of nomenclature covers "all organisms traditionally treated as algae, fungi, or plants, whether fossil or non-fossil, including blue-green algae (Cyanobacteria), chytrids, oomycetes, slime moulds and photosynthetic protists with their taxonomically related non-photosynthetic groups (but excluding Microsporidia)."The purpose of a formal name is to have a single name that is accepted and used worldwide for a particular plant or plant group. For example, the botanical name Bellis perennis denotes a plant species which is native to most of the countries of Europe and the Middle East, where it has accumulated various names in many languages. Later, the plant was introduced worldwide, bringing it into contact with more languages. English names for this plant species include: daisy, English daisy, and lawn daisy. The cultivar Bellis perennis 'Aucubifolia' is a golden-variegated horticultural selection of this species.


Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus Equus. Equidae belongs to the order Perissodactyla, which includes the extant tapirs and rhinoceros, and several extinct families.

The term equid refers to any member of this family, including any equine.


Euphorbia is a very large and diverse genus of flowering plants, commonly called spurge, in the spurge family (Euphorbiaceae). "Euphorbia" is sometimes used in ordinary English to collectively refer to all members of Euphorbiaceae (in deference to the type genus), not just to members of the genus. Some euphorbias are commercially widely available, such as poinsettias at Christmas. Some are commonly cultivated as ornamentals, or collected and highly valued for the aesthetic appearance of their unique floral structures, such as the crown of thorns plant (Euphorbia milii). Euphorbias from the deserts of Southern Africa and Madagascar have evolved physical characteristics and forms similar to cacti of North and South America, so they (along with various other kinds of plants) are often incorrectly referred to as cacti. Some are used as ornamentals in landscaping, because of beautiful or striking overall forms, and drought and heat tolerance.Euphorbias range from tiny annual plants to large and long-lived trees. The genus has over or about 2,000 members, making it one of the largest genera of flowering plants. It also has one of the largest ranges of chromosome counts, along with Rumex and Senecio. Euphorbia antiquorum is the type species for the genus Euphorbia. It was first described by Carl Linnaeus in 1753 in Species Plantarum.

The plants share the feature of having a poisonous, milky, white, latex-like sap, and unusual and unique floral structures. The genus may be described by properties of its members' gene sequences, or by the shape and form (morphology) of its heads of flowers. When viewed as a whole, the head of flowers looks like a single flower (a pseudanthium). It has a unique kind of pseudanthium, called a cyathium, where each flower in the head is reduced to its barest essential part needed for sexual reproduction. The individual flowers are either male or female, with the male flowers reduced to only the stamen, and the females to the pistil. These flowers have no sepals, petals, or other parts that are typical of flowers in other kinds of plants. Structures supporting the flower head and beneath have evolved to attract pollinators with nectar, and with shapes and colors that function the way petals and other flower parts do in other flowers. It is the only genus of plants that has all three kinds of photosynthesis, CAM, C3, and C4.The genus can be found all over the world. The forms range from annual plants lying on the ground, to well-developed tall trees. In deserts in Madagascar and southern Africa, convergent evolution has led to cactus-like forms where the plants occupy the same ecological niche as cacti do in deserts of North and South America. The genus is primarily found in the tropical and subtropical regions of Africa and the Americas, but also in temperate zones worldwide. Succulent species originate mostly from Africa, the Americas, and Madagascar. A wide range of insular species can be found.


Falcons () are birds of prey in the genus Falco, which includes about 40 species. Falcons are widely distributed on all continents of the world except Antarctica, though closely related raptors did occur there in the Eocene.Adult falcons have thin, tapered wings, which enable them to fly at high speed and change direction rapidly. Fledgling falcons, in their first year of flying, have longer flight feathers, which make their configuration more like that of a general-purpose bird such as a broad-wing. This makes flying easier while learning the exceptional skills required to be effective hunters as adults. There are many different types of falcon.

The falcons are the largest genus in the Falconinae subfamily of Falconidae, which itself also includes another subfamily comprising caracaras and a few other species. All these birds kill with their beaks, using a "tooth" on the side of their beaks—unlike the hawks, eagles, and other birds of prey in the Accipitridae, which use their feet.

The largest falcon is the gyrfalcon at up to 65 cm in length. The smallest falcons are the kestrels, of which the Seychelles kestrel measures just 25 cm. As with hawks and owls, falcons exhibit sexual dimorphism, with the females typically larger than the males, thus allowing a wider range of prey species.Some small falcons with long, narrow wings are called "hobbies" and some which hover while hunting are called "kestrels".As is the case with many birds of prey, falcons have exceptional powers of vision; the visual acuity of one species has been measured at 2.6 times that of a normal human. Peregrine falcons have been recorded diving at speeds of 200 miles per hour (320 km/h), making them the fastest-moving creatures on Earth. The fastest recorded dive for one is 390 km/h.


Fraxinus , English name ash, is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45–65 species of usually medium to large trees, mostly deciduous, though a few subtropical species are evergreen. The genus is widespread across much of Europe, Asia, and North America.The tree's common English name, "ash", traces back to the Old English æsc which relates to the Proto-Indo-European for the tree, while the generic name originated in Latin from a Proto-Indo-European word for birch. Both words are also used to mean "spear" in their respective languages as the wood is good for shafts. The leaves are opposite (rarely in whorls of three), and mostly pinnately compound, simple in a few species. The seeds, popularly known as "keys" or "helicopter seeds", are a type of fruit known as a samara. Most Fraxinus species are dioecious, having male and female flowers on separate plants but gender in ash is expressed as a continuum between male and female individuals, dominated by unisexual trees. With age, ash may change their sexual function from predominantly male and hermaphrodite towards femaleness; if grown as an ornamental and both sexes are present, ashes can cause a considerable litter problem with their seeds. Rowans or mountain ashes have leaves and buds superficially similar to those of true ashes, but belong to the unrelated genus Sorbus in the rose family.


Homo (Latin: homō, "human being") is the genus which emerged in the otherwise extinct Australopithecus genus that encompasses the extant species Homo sapiens (modern humans), plus several extinct species classified as either ancestral to or closely related to modern humans (depending on a species), most notably Homo erectus and Homo neanderthalensis.

The genus is taken to emerge with the appearance of Homo habilis, just over two million years ago. Genus Homo, together with the genus Paranthropus is probably sister to A. africanus in the genus Australopithecus, which itself had previously split from the lineage of Pan, the chimpanzees.Homo erectus appeared about two million years ago and, in several early migrations, it spread throughout Africa (where it is dubbed Homo ergaster) and Eurasia.

It was likely the first human species to live in a hunter-gatherer society and to control fire.

An adaptive and successful species, Homo erectus persisted for more than a million years, and gradually diverged into new species by around 500,000 years ago.Homo sapiens (anatomically modern humans) emerges close to 300,000 to 200,000 years ago, most likely in Africa, and Homo neanderthalensis emerged at around the same time in Europe and Western Asia.

H. sapiens dispersed from Africa in several waves, from possibly as early as 250,000 years ago, and certainly by 130,000 years ago, the so-called Southern Dispersal beginning about 70,000 years ago leading to the lasting colonisation of Eurasia and Oceania by 50,000 years ago.

Both in Africa and Eurasia, H. sapiens met with and interbred with archaic humans. Separate archaic (non-sapiens) human species are thought to have survived until around 40,000 years ago (Neanderthal extinction), with possible late survival of hybrid species as late as 12,000 years ago (Red Deer Cave people).


Iguana (, Spanish: [iˈɣwana]) is a genus of herbivorous lizards that are native to tropical areas of Mexico, Central America, South America, and the Caribbean. The genus was first described in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his book Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena. Two species are included in the genus Iguana: the green iguana, which is widespread throughout its range and a popular pet, and the Lesser Antillean iguana, which is native to the Lesser Antilles and endangered due to habitat destruction and hybridization with introduced green iguanas.

The word "iguana" is derived from the original Taino name for the species, iwana.In addition to the two species in the genus Iguana, several other related genera in the same family have common names of the species including the word "iguana".


The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (hares and rabbits) and the Ochotonidae (pikas). The name of the order is derived from the Ancient Greek lagos (λαγώς, "hare") + morphē (μορφή, "form"). There are about eighty-seven extant species of lagomorph, including about twenty-nine species of pika, twenty-eight species of rabbit and cottontail, and thirty species of hare.Lagomorphs share a common ancestor with rodents, together forming the clade Glires (Latin: "dormice"). Like the ancestors of most modern mammalian groups, this most recent common ancestor lived after the last great extinction event, the K–Pg extinction 66 million years ago that drove all dinosaurs except birds to extinction. Early lagomorphs arose perhaps in Asia and spread across the northern hemisphere. Later, rodents came to dominate more environmental niches, and lagomorphs seem to have been in decline.


Malus ( or ) is a genus of about 30–55 species of small deciduous trees or shrubs in the family Rosaceae, including the domesticated orchard apple (M. pumila syn. M. domestica ) – also known as the eating apple, cooking apple, or culinary apple. The other species are generally known as crabapples, crab apples, or wild apples.

The genus is native to the temperate zone of the Northern Hemisphere.


Acer is a genus of trees and shrubs commonly known as maple. The genus is placed in the family Sapindaceae. There are approximately 128 species, most of which are native to Asia, with a number also appearing in Europe, northern Africa, and North America. Only one species, Acer laurinum, extends to the Southern Hemisphere. The type species of the genus is the sycamore maple, Acer pseudoplatanus, the most common maple species in Europe. The maples have easily recognizable palmate leaves and distinctive winged fruits. The closest relatives of the maples are the horse chestnuts.

Monotypic taxon

In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon.A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispecific" or "monospecific" is sometimes preferred.

In botanical nomenclature, a monotypic genus is a genus in the special case where a genus and a single species are simultaneously described.In contrast an oligotypic taxon contains more than one but only a very few subordinate taxa.


A raven is one of several larger-bodied species of the genus Corvus. These species do not form a single taxonomic group within the genus.

There is no consistent distinction between "crows" and "ravens", and these appellations have been assigned to different species chiefly on the basis of their size, crows generally being smaller than ravens.

The largest raven species are the common raven and the thick-billed raven.

Taxonomic rank

In biological classification, taxonomic rank is the relative level of a group of organisms (a taxon) in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, order, class, phylum, kingdom, domain, etc.

A given rank subsumes under it less general categories, that is, more specific descriptions of life forms. Above it, each rank is classified within more general categories of organisms and groups of organisms related to each other through inheritance of traits or features from common ancestors. The rank of any species and the description of its genus is basic; which means that to identify a particular organism, it is usually not necessary to specify ranks other than these first two.Consider a particular species, the red fox, Vulpes vulpes: the next rank above, the genus Vulpes, comprises all the "true" foxes. Their closest relatives are in the immediately higher rank, the family Canidae, which includes dogs, wolves, jackals, and all foxes; the next higher rank, the order Carnivora, includes caniforms (bears, seals, weasels, skunks, raccoons and all those mentioned above), and feliforms (cats, civets, hyenas, mongooses). Carnivorans are one group of the hairy, warm-blooded, nursing members of the class Mammalia, which are classified among animals with backbones in the phylum Chordata, and with them among all animals in the kingdom Animalia. Finally, at the highest rank all of these are grouped together with all other organisms possessing cell nuclei in the domain Eukarya.

The International Code of Zoological Nomenclature defines rank as: "The level, for nomenclatural purposes, of a taxon in a taxonomic hierarchy (e.g. all families are for nomenclatural purposes at the same rank, which lies between superfamily and subfamily)."

Tube-dwelling anemone

Tube-dwelling anemones or ceriantharians look very similar to sea anemones but belong to an entirely different subclass of anthozoans. They are solitary, living buried in soft sediments. Tube anemones live inside and can withdraw into tubes, which are composed of a fibrous material made from secreted mucus and threads of nematocyst-like organelles known as ptychocysts. Ceriantharians were formerly classified in the taxon Ceriantipatharia along with the black corals but have since been moved to their own subclass, Ceriantharia.

Ceriantharians have a crown of tentacles that are composed of two whorls of distinctly different sized tentacles. The outer whorl consists of large tentacles that extend outwards. These tentacles taper to points and are mostly used in food capture and defence. The smaller inner tentacles are held more erect than the larger lateral tentacles and are used for food manipulation and ingestion.A few species such as Anactinia pelagica are pelagic and are not attached to the bottom; instead, they have a gas chamber within the pedal disc, allowing them to float upside down near the surface of the water.

Type species

In zoological nomenclature, a type species (species typica) is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen(s). A similar concept is used for suprageneric groups called a type genus.

In botanical nomenclature, these terms have no formal standing under the code of nomenclature, but are sometimes borrowed from zoological nomenclature. In botany, the type of a genus name is a specimen (or, rarely, an illustration) which is also the type of a species name. The species name that has that type can also be referred to as the type of the genus name. Names of genus and family ranks, the various subdivisions of those ranks, and some higher-rank names based on genus names, have such types.In bacteriology, a type species is assigned for each genus.Every named genus or subgenus in zoology, whether or not currently recognized as valid, is theoretically associated with a type species. In practice, however, there is a backlog of untypified names defined in older publications when it was not required to specify a type.

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