Order (Latin:ordo) is one of the eight majorhierarchical taxonomic ranks inLinnaean taxonomy. It is classified betweenfamily and class. Inbiological classification, the order is ataxonomic rank used in the classification of organisms and recognized by thenomenclature codes. An immediately higher rank,superorder, is sometimes added directly above order, withsuborder directly beneath order. An order can also be defined as a group of related families.
What does and does not belong to each order is determined by ataxonomist, as is whether a particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognized only rarely.[1]
In their 1997 classification ofmammals,McKenna and Bell used two extra levels between superorder and order:grandorder andmirorder.[5] Michael Novacek (1986) inserted them at the same position.Michael Benton (2005) inserted them between superorder and magnorder instead.[6] This position was adopted bySystema Naturae 2000 and others.
Inbotany, the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order.[7] Any number of further ranks can be used as long as they are clearly defined.[7]
The superorder rank is commonly used, with the ending-anae that was initiated byArmen Takhtajan's publications from 1966 onwards.[8]
The order as a distinct rank of biological classification having its own distinctive name (and not just called ahigher genus (genus summum)) was first introduced by the German botanistAugustus Quirinus Rivinus in his classification of plants that appeared in a series of treatises in the 1690s.Carl Linnaeus was the first to apply it consistently to the division of all three kingdoms of nature (thenminerals,plants, andanimals) in hisSystema Naturae (1735, 1st. Ed.).
Title page of the 1758 edition of Linnaeus'sSystema Naturæ.[9]
For plants, Linnaeus' orders in theSystema Naturae and theSpecies Plantarum were strictly artificial, introduced to subdivide the artificial classes into more comprehensible smaller groups. When the wordordo was first consistently used for natural units of plants, in 19th-century works such as theProdromus Systematis Naturalis Regni Vegetabilis ofAugustin Pyramus de Candolle and theGenera Plantarum of Bentham & Hooker, it indicated taxa that are now given the rank of family (seeordo naturalis, 'natural order').
In French botanical publications, fromMichel Adanson'sFamilles naturelles des plantes (1763) and until the end of the 19th century, the wordfamille (plural:familles) was used as a French equivalent for this Latinordo. This equivalence was explicitly stated in theAlphonse Pyramus de Candolle'sLois de la nomenclature botanique (1868), the precursor of the currently usedInternational Code of Nomenclature for algae, fungi, and plants.
In the first internationalRules ofbotanical nomenclature from theInternational Botanical Congress of 1905, the wordfamily (familia) was assigned to the rank indicated by the Frenchfamille, while order (ordo) was reserved for a higher rank, for what in the 19th century had often been named a 'cohort' (cohors,[10] pluralcohortes).
Some of the plant families still retain the names of Linnaean "natural orders" or even the names of pre-Linnaean natural groups recognized by Linnaeus as orders in his natural classification (e.g.Palmae orLabiatae). Such names are known asdescriptive family names.
In the field ofzoology, the Linnaean orders were used more consistently. That is, the orders in the zoology part of theSystema Naturae refer to natural groups. Some of his ordinal names are still in use, e.g.Lepidoptera (moths and butterflies) andDiptera (flies, mosquitoes, midges, and gnats).[11]
From 1991 to 2017, order was the highest rank used toclassify viruses in a system that ranged from order to species. In 2018, theInternational Committee on Taxonomy of Viruses, which overseesvirus taxonomy, added ranks higher than order up to the highest taxonomic rank ofrealm. Virus orders are indicated by the suffix -virales.[12][13]
^Carl von Linné, translated byWilliam Turton (1806).Volume 2: Insects. A general system of nature: through the three grand kingdoms of animals, vegetables, and minerals, systematically divided into their several classes, orders, genera, species, and varieties. London: Lackington, Allen, and Co.
