Difference between Indented Key and Bracketed Key

Hola Taxonomists! Let’s get to know taxonomic keys better! Rapid identification of unknown plants is possible with the help of specialised tools called taxonomic keys. Significant taxonomic literature like flora, manuals, and monographs have taxonomic keys for taxonomists to conduct research effectively. The idea of taxonomic keys is based on reliable and stable characters. Two essential types of single access taxonomic keys are – Indented Key and Bracketed Key.

What are Single Access Keys?

To begin with, the single access or sequential keys are based on specific diagnostic characters. They have been divided into- Serial Key, Indented Key and Bracketed Key. Understanding the difference between indented key and bracketed key is particularly important for the field of taxonomy. They have pairs of contrasting choices and hence are called dichotomous keys.

In the construction of dichotomous keys, a list of reliable characters is prepared for the taxon for which the key is to be developed. For each character, two contrasting choices are determined ( Eg. Habit- Herbaceous or Woody). The two contrasting choices form a couplet and each choice is called a lead. Another key point is that for characters that have more than 2 available contrasting choices, characters are made dichotomous by the process of splitting.

Sequential keys were first introduced by J.P. Lamarck in Flore Francaise (1778).

Difference between Indented Key and Bracketed Key

Indented/ Yoked Key is a commonly used key in taxonomic literature. Following are the important features of this key are-

1. The leads and taxa are arranged in specialised visual groups called yokes. 
2. The subordinate couplets are intentionally indented below the first/ primary one at a particular distance from the margin.
3. It is highly useful in the case of shorter taxonomic keys.
4. In the case of longer keys, the key becomes extensively sloping and there is wastage of paper space.

For instance, this type of sequential key was used in Flora Europea for Genus Sonchus. 

Bracketed/ Parallel Key is another commonly used key in the field of plant systematics. Following are the important features of this key are-

1. The couplet with the contrasting choices called leads are always together.
2. The subordinate couplets are at the same distance from the margin.
3. Its arrangement is useful in the case of longer keys.
4. The leads of the couplet stay together nevertheless so there is no wastage of paper.

This type of sequential key has been used in larger floras like Flora USSR and Flora of  British Isles.

Guidelines for Dichotomous Keys

Both Indented Key and Bracketed Key are examples of dichotomous keys. Following are certain guidelines that should be followed while developing such keys are-

1. The keys should be strictly and solely dichotomous i.e. the couplets should have only 2 leads or contrasting choices.
2. Selection one lead should automatically lead to the rejection of the other contrasting one ie. the two leads of a couplet should be strictly mutually exclusive.
3. Moreover, the initial word of the two leads of a couplet should be common.
4. There should be no overlapping in the statements of the lead.
5. Vegetative and reproductive characteristics should be particularly be incorporated in separate keys for identification of trees.
6. Confusing and vague statements do not qualify as leads.
7. There is a need to prefix the leads with numbers or letters.
8. In case of dioecous plants, two separate keys are to be developed for male and female flowers.

Computer-stored Keys

Dichotomous keys like Intended Key and Bracketed Key can be fed in a computer system and run by the application of appropriate program. The computer system begins with the first couplet and enquires about the attribute in the plant for identification purpose. Based on the information entered and via relevant questions, identification can be achieved.

Computer-stored keys are a modern day technique in the field of plant systematics.

To summarize taxonomy forms the basis for all other fields of biology. So dear biologists, keep reading at MBD to master your fundamental concepts!

Team MBD

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For more information on Taxonomic Keys checkout Taxonomic Keys: Meaning, Suggestions and Types (biologydiscussion.com)