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• A taxonomic Key is a most useful tool in taxonomy for the identification of an
• 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
• 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)
• 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
• 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
• 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.
• 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.
• Key that concentrate on making identification most convenient and reliable.
• May be designed for field work or laboratory work.
• 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
• 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
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
• Not useful in identification of all specimens.