Identification key

Template:Short description In biology, an identification key, taxonomic key, or frequently just key, is a printed or computer-aided device that aids in the identification of biological organisms.

Historically, the most common type of identification key is the dichotomous key, a type of single-access key which offers a fixed sequence of identification steps, each with two alternatives. The earliest examples of identification keys originate in the seventeenth, but their conceptual history can be traced back to antiquity. Modern multi-access keys allow the user to freely choose the identification steps and any order. They were traditionally performed using punched cards but now almost exclusively take the form of computer programs.

HistoryEdit

File:Lamarck's key.png

Identification key published in Lamarck's Flore française, Volume 1.

The conceptual origins of the modern identification key can be traced back to antiquity. Theophrastus categorized organisms into "subdivisions" based on dichotomous characteristics. The seventeenth-century Chinese herbalist, Pao Shan, in his treatise Yeh-ts'ai Po-Iu, included a systematic categorization of plants based on their apparent characteristics specifically for the purposes of identification.<ref name=":2" />Template:Rp

Seventeenth-century naturalists, including John Ray, Rivinius, and Nehemiah Grew, published examples of bracketed tables. However, these examples were not strictly keys in the modern sense of an analytical device used to identify a single specimen, since they often did not lead to a single end point, and instead functioned more as synopses of classification schemes.<ref name=":2" />Template:Rp

The first analytical identification key is credited to Lamarck who included several in his 1778 book, Flore Françoise. Lamarck's key follows more or less the same design as the modern dichotomous, bracketed key.<ref name=":2" />Template:Rp

Alphonso Wood was the first American to use identification keys in 1845. Other early instances of keys are found in the works of Asa Gray and W. H. Evans.<ref name=":2" />Template:Rp

TerminologyEdit

Identification keys are known historically and contemporarily by many names, including analytical key, entomological key, artificial key,<ref name=":2" /> diagnostic key,<ref name=":3" /> determinator,<ref name=":0" /> and taxonomic key<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Within the biological literature, identification keys are referred to simply as keys.<ref>Template:Cite book</ref> They are also commonly referred to in general as dichotomous keys,<ref name=":5">Template:Cite book</ref> though this term strictly refers to a specific type of identification key (see Types of keys).

UseEdit

Identification keys are used in systematic biology and taxonomy to identify the genus or species of a specimen organism from a set of known taxa. They are commonly used in the fields of microbiology, plant taxonomy, and entomology, as groups of related taxa in these fields tend to be very large.<ref name=":0">Template:Cite book</ref> However, they have also been used to classify non-organisms, such as birds nests, and in non-biological sciences such as geology.<ref name=":2">Template:Cite journal</ref>Template:Rp Similar methods have also been used in computer science<ref>Template:Cite encyclopedia</ref>

A user of a key selects from a series of choices, representing mutually exclusive features of the specimen, with the aim to arrive at the sole remaining identity from the group of taxa.<ref name=":1">Template:Cite book</ref> Each step in the key employs a character: a distinguishing feature of an organism that is conveniently observable.<ref name=":0" />

Types of keysEdit

Identification keys are sometimes also referred to as artificial keys to differential them from other diagrams that visualize a classification schemes, often in the form of a key or tree structure. These diagrams are called natural keys or synopses and are not used for identifying specimens. In contrast, an artificial identification key is a tool that utilizes characters that are the easiest to observe and most practical for arriving at an identity.<ref name=":3" />Template:Rp<ref name=":5" />Template:Rp Identification keys can be divided into two main types.

Single-access keyEdit

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}

File:Screenshot from 2024-10-20 20-19-32.png

User interaction steps in a single-access key. The sequence of steps follow the data structure.

A single-access key (also called a sequential key or an analytical key), has a fixed structure and sequence. The user must begin at the first step of the key and proceed until the end. A single-access key has steps that consist of two mutually exclusive statements (leads) is called a dichotomous key. Most single-access keys are dichotomous.<ref name=":0" /> A single-access key with more than two leads per step is referred to as polytomous.<ref name=":4">Template:Cite book</ref>

Presentational variantsEdit

Dichotomous keys can be presented in two main styles: linked and nested. In the linked style (also referred to as open, parallel, linked, and juxtaposition<ref name=":4" />Template:Rp), each pair of leads (called a couplet) are printed together. In the nested style (also referred to as closed, yoked, and indented<ref name=":4" />Template:Rp), the subsequent steps after choosing a lead are printed directly underneath it, in succession. To follow the second lead of the couplet, the user must skip over the nested material that follows logically from the first lead of the couplet.<ref name=":3">Template:Cite book</ref> Nested keys are more commonly known as indented, but unfortunately this refers to an accidental (albeit frequent) rather than essential quality. Nested keys may be printed without indentation to preserve space (relying solely on corresponding lead symbols) and linked keys may be indented to enhance the visibility of the couplet structure.<ref name=":4" />Template:Rp

Multi-access keysEdit

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}

File:Multi-access key.png

User interaction steps in a multi-access key. The sequence of steps is determined by the user.

A multi-access key (free-access key,<ref name=":4" /> or polyclave<ref name=":1" />) allows a user to specify characters in any order. Therefore, a multi-access key can be thought of as "the set of all possible single-access keys that arise by permutating the order of characters."<ref name=":4" />Template:Rp While there are print versions of multi-access keys, they were historically created using punched card systems.<ref name=":1" /> Today, multi-access keys are computer-aided tools.<ref name=":4" />Template:Rp

Key constructionEdit

An early attempt to standardize the construction of keys was offered by E. B. Williamson in the June 1922 volume of Science.<ref>Template:Cite journal</ref> More recently, Richard Pankhurst published a guidelines and practical tips for key construction in a section of his 1978 book, Biological Identification.<ref name=":3" />Template:Rp

Identification errors may have serious consequences in both pure and applied disciplines, including ecology, medical diagnosis, pest control, forensics, etc.<ref>Template:Cite journal</ref>

Computer-aided key constructionEdit

The first computer programs for constructing identification keys were created in the early 1970s.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Since then, several popular programs have been developed, including DELTA, XPER, and LucID.<ref name=":0" />Template:Rp

Single-access keys, until recently, have been developed only rarely as computer-aided, interactive tools. Noteworthy developments in this area are the commercial LucID Phoenix application, the FRIDA/Dryades software, the KeyToNature Open Key Editor, and the open source WikiKeys and jKey application on biowikifarm.<ref name=":4" />Template:Rp

ReferencesEdit

Template:Reflist Template:Free-content attribution

External linksEdit

Template:Sister project Template:Wikiversity