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Taxonomic key

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S
SaharshanSalam

This document provides information about taxonomic keys, which are tools used in taxonomy to identify unknown organisms. It defines taxonomic keys and their purpose of using diagnostic characteristics to lead to the identification of a species or genus. It then describes different types of single access keys, including dichotomous, bracket, indented, serial, and grouped keys. It also discusses multi-access keys and styles of presenting keys, as well as advantages and disadvantages of using taxonomic keys.

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TAXONOMIC KEY Submitted by Saharshan P M IV Z
TAXONOMIC KEY • A taxonomic Key is a most useful tool in taxonomy for the identification of an unknown organism. • The object of the key is to separate and segregate diagnostic characters in such a way that it provide a safe road to identification. • The ultimate goal of taxonomic key is the identification of taxa ( species or genus). • It is a tabulation of diagnostic characters of a species in dichotomous couplets facilitating rapid identification for classification. • Taxonomic Key can be generally categorized into two; I. Single access Key II. Multi access Key
SINGLE ACCESS KEYS • Also known as sequential key, analytical key , pathway key. • Almost all single access keys are dichotomous(dividing into pairs) keys. • It consists of opposing statements(leads), each statements leading to another pair of choices(couplets),sequentially narrowing the user’s search down until a final statement identifies the organism. • These days different kinds of keys are used in taxonomic works. Most important ones are listed below.
1. Simple dichotomous Keys • Couplets are composed of alternatives for ready comparison. • Gives a slight inconvenience in tracing backward.
2. Simple Bracket Key • Almost similar to preceding one except that numbers of couplets showing the continuation in the key are shown after main numbers. • One can easily run through this key both forward and backward.
3. Indented Key • In this key couplets are indented from the left hand margin based on their importance. • Advantageous in that relationship of various divisions is quite apparent. • Disadvantage is that , the alternatives are widely separated.
4. Serial Key • Similar to indented key in having species arranged according to the number of key characters in common. • Here also , alternatives are widely separated
5. Grouped type Key • First member of primary couplet is set up, subsequent couplets are arranged beneath it and labelled 2,3,4..to the end of the first member of primary couplet. • Numbers may be little bit confusious.
6. Combination Key • Combination of both indented key and either simple dichotomous key/grouped type key.Advantageous in that it makes primary secondary and tertiary groups conspicuous
7.Pictorial Key • Keys provided with characters along with the figures in a comparative manner. • Specially meant for field workers and non-taxonomists
8. Branching Key • Meant for easy and quick separation of species. • Quite useful for field workers.
9.Circular Key • Designed for quick and immediate identification of commonly occurring species.
10.Box type Key • It is also meant for field workers and useful for quick identification.
DIAGNOSTIC KEY • Key that concentrate on making identification most convenient and reliable. • May be designed for field work or laboratory work.
SYNOPTIC KEY • Key which aims to reflect the scientific classification of an organism. It follows taxonomic classification as close as possible. • This may require instruments like hand lens, microscope etc.
TAXONOMIC KEY PRESENTATION Single access keys can be presented in different styles.Most frequently encountered styles are given. I. Nested Style: All couplets immediately followed the lead at the expense of separating the leads within a couplet. The most frequent sub-type of nested keys are called ‘indented key’. II. Linked Style: Leads within a couplet immediately follow each other making polytomous keys easy to archieve.
COMPUTER AIDED KEY • In recent years, computer technology has been used for constructing keys. • Figures , photographs etc can be fed into computer with the help of appropriate programmes. • It is much more easier and less time consuming to compare the characters of unknown taxa with known taxa. • Scanners of computer can observe and record the characters of undetermined taxa and compare these with those of already known • DELTA( Description Language for Taxonomy) is a useful system of programmes for recording taxonomic descriptions for processing by computer. • It generates conventional identification keys.
MERITS OF KEYS • Facilitates identification of specimen • Key is dichotomous offering two alternatives at any point. • Easy to apply • Provides best assurance for correct identification. • It provides tools for taxonomic analysis since in the preparation of key, one must select, evaluate and arrange taxonomic characters. • Key characters apply equally to all individuals of the population regardless of age and size.
DEMERITS OF KEYS • Construction of key is a time consuming task. • Key does not provide biological and phylogenetic characters. • It does not provide information of cytological and molecular characters of a specimen. • Not useful in identification of all specimens.
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Taxonomic key

  • 2. TAXONOMIC KEY • A taxonomic Key is a most useful tool in taxonomy for the identification of an unknown organism. • The object of the key is to separate and segregate diagnostic characters in such a way that it provide a safe road to identification. • The ultimate goal of taxonomic key is the identification of taxa ( species or genus). • It is a tabulation of diagnostic characters of a species in dichotomous couplets facilitating rapid identification for classification. • Taxonomic Key can be generally categorized into two; I. Single access Key II. Multi access Key
  • 3. SINGLE ACCESS KEYS • Also known as sequential key, analytical key , pathway key. • Almost all single access keys are dichotomous(dividing into pairs) keys. • It consists of opposing statements(leads), each statements leading to another pair of choices(couplets),sequentially narrowing the user’s search down until a final statement identifies the organism. • These days different kinds of keys are used in taxonomic works. Most important ones are listed below.
  • 4. 1. Simple dichotomous Keys • Couplets are composed of alternatives for ready comparison. • Gives a slight inconvenience in tracing backward.
  • 5. 2. Simple Bracket Key • Almost similar to preceding one except that numbers of couplets showing the continuation in the key are shown after main numbers. • One can easily run through this key both forward and backward.
  • 6. 3. Indented Key • In this key couplets are indented from the left hand margin based on their importance. • Advantageous in that relationship of various divisions is quite apparent. • Disadvantage is that , the alternatives are widely separated.
  • 7. 4. Serial Key • Similar to indented key in having species arranged according to the number of key characters in common. • Here also , alternatives are widely separated
  • 8. 5. Grouped type Key • First member of primary couplet is set up, subsequent couplets are arranged beneath it and labelled 2,3,4..to the end of the first member of primary couplet. • Numbers may be little bit confusious.
  • 9. 6. Combination Key • Combination of both indented key and either simple dichotomous key/grouped type key.Advantageous in that it makes primary secondary and tertiary groups conspicuous
  • 10. 7.Pictorial Key • Keys provided with characters along with the figures in a comparative manner. • Specially meant for field workers and non-taxonomists
  • 11. 8. Branching Key • Meant for easy and quick separation of species. • Quite useful for field workers.
  • 12. 9.Circular Key • Designed for quick and immediate identification of commonly occurring species.
  • 13. 10.Box type Key • It is also meant for field workers and useful for quick identification.
  • 14. DIAGNOSTIC KEY • Key that concentrate on making identification most convenient and reliable. • May be designed for field work or laboratory work.
  • 15. SYNOPTIC KEY • Key which aims to reflect the scientific classification of an organism. It follows taxonomic classification as close as possible. • This may require instruments like hand lens, microscope etc.
  • 16. TAXONOMIC KEY PRESENTATION Single access keys can be presented in different styles.Most frequently encountered styles are given. I. Nested Style: All couplets immediately followed the lead at the expense of separating the leads within a couplet. The most frequent sub-type of nested keys are called ‘indented key’. II. Linked Style: Leads within a couplet immediately follow each other making polytomous keys easy to archieve.
  • 17. COMPUTER AIDED KEY • In recent years, computer technology has been used for constructing keys. • Figures , photographs etc can be fed into computer with the help of appropriate programmes. • It is much more easier and less time consuming to compare the characters of unknown taxa with known taxa. • Scanners of computer can observe and record the characters of undetermined taxa and compare these with those of already known • DELTA( Description Language for Taxonomy) is a useful system of programmes for recording taxonomic descriptions for processing by computer. • It generates conventional identification keys.
  • 18. MERITS OF KEYS • Facilitates identification of specimen • Key is dichotomous offering two alternatives at any point. • Easy to apply • Provides best assurance for correct identification. • It provides tools for taxonomic analysis since in the preparation of key, one must select, evaluate and arrange taxonomic characters. • Key characters apply equally to all individuals of the population regardless of age and size.
  • 19. DEMERITS OF KEYS • Construction of key is a time consuming task. • Key does not provide biological and phylogenetic characters. • It does not provide information of cytological and molecular characters of a specimen. • Not useful in identification of all specimens.