Principles of identification

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Names are important
Butterflies from Schmidt’s Entomology Collection (Slovenian Museum of Natural History Ljubljana)
Author: Bob Press, Natural History Museum (London, UK)

Names are important. Once the name of an object is known, all kinds of information about it can be found. For an organism this can include facts such as whether it is edible or poisonous, or has economic value. A name can also be used to infer other information. For example, the presence of a particular species may indicate the quality of air or water at that location. A wrong name is misleading. Only with a correct name can information pertinent to the species be unlocked and to arrive at this name the species needs to be accurately identified.

Reliable identification of organisms is not only important to science but also throughout society (e.g. pathogens in health care, pests in agriculture, monitoring ecosystems, detecting invasive species, import/export regulation) and has an impact on all aspects of our lives.

How we identify an organism

All organisms have features or characteristics which consistently distinguish one species from another, and recognizing these features is the core of identification. The process involves comparing a specimen with reference data (which may include text descriptions, illustrations, sound, or other data such as DNA sequences). Specimens which do not match the description of any known species are new to science.

Comparing a specimen with the descriptions of every known species is a laborious and very inefficient method of identification, so a variety of tools - keys - are used to speed up the process.

How identificaton keys work

Computer-aided dichotomous identification key

Keys ask a series of questions, the answers to which lead to the most likely name of the correct species. The specimen can then be compared to the detailed description of that species to confirm the identification. The larger the taxonomic group that is keyed out, the longer the key and the greater the risk of making an error in the process. There are keys for most known groups of organisms. Users dealing with a potentially wide range of organisms need access to a library of keys, and a network of specialists to consult. So correct species identification is a precise process, for which expert knowledge is often needed.

Traditional keys are commonly dichotomous, guiding the user through the identification process by presenting a stepwise sequence of choices. Terminology and lack of illustrations often make these keys hard to use for non-experts.

Computer-aided keys make identifying species easier because the keys can be interactive, for example suggesting the best separating character to use for a quick identification. The latest method for identifying species, referred to as bar-coding, is based on genetic information. All species have a unique genetic pattern (the bar-code). By comparing the bar-code with a database of all other bar-codes, the species name is found. This method is discovering species which are not identifiable by other methods but the technology is very recent and scientists are still building up the database of authenticated bar-codes.

Why we use Latin (scientific) names

Carl Linne - Swedish botanist who laid the foundations for modern biological nomenclature

Names are labels, and how we apply them is just as important as what the names are. Aliases can be very confusing, so scientists follow strict rules about names. In addition, scientists use Latin names rather than those in the languages of different countries and regard these Latin names as the 'real' ones. There are good reasons for this, mostly relating to identification.

Local or common names vary from region to region. For example, the English name Cuckoo-flower (and direct translations) is widely used in the UK, Holland, Germany and other N. European regions for Cardamine pratensis, a member of the cabbage family which grows in damp meadows. This plant has at least 50 other common names in the UK alone. Cuckoo-flower is also frequently used for three other, entirely unrelated, plants - one of them a rare orchid, another bearing poisonous berries. Using this name easily leads to misidentification, with confusing and potentially disastrous results.

Latin or scientific names are universal, applying to the same organism wherever it occurs. They are binomials, that is they consist of two parts - the genus followed by the species - in the same way we have a surname and a forename (in that order). The full name always consists of both parts. Again, like our own names, they convey information about relationships and shared similarities. Some plants have no common name, so the scientific name is the only one which can be used.