Plant identification-taxonomic keys

Plant identification-taxonomic keys:-

Plant identification:- It uses anatomical and morphological clues to compare known plants with unknown plants.

Taxonomic Keys:- It is a device used for identification of plants and animals consisting of a series of contrasting / contradictory statements or propositions requiring the identifier to make comparisons and decisions based on statements in the key as related to the material to be identified. These were first published by Jean Baptiste – Lamarck in 1778. Helps in quick identification of unknown plant. They are of 2 types:

1. Single Access key (Dichotomous keys)

2. Multi Access key (Poly clave keys)

1. Single Access Key (Dichotomous keys):- In phylogenetics a Single access key is an identification key where the sequence and structure of identification steps is fixed by the Author of the key.

> Single access keys are closely related to decision trees or self balancing binary search trees.

> Always a choice between two contradictory statements is provided.

> One is accepted and one is rejected.

> Each statement is called LEAD and single pair of lead is called couplet.

> Types of Single Access Keys:

a. Indented key/yoked key:- Indents the leads of the couplet a equal distance from the left margin.

The two choices are labelled 1 and1’ or 1a and 1b.

b. Bracketed key:- Both choices are given side by side. Choices are numbered/lettered.

Indented key on Rhododendron:-

Bracketed key on Rhododendron:-

2. Multi Access key (Poly clave keys):- 

> Another type of key, which is relatively a new alternative to dichotomous keys and becoming increasingly popular, especially because of the ease of computerizing them, is termed multiple access or poly clave or synoptic key. The advantage of these keys is that they allow the user to enter the key at any point.

> This key is based on the identification of organisms by a process of elimination. In a written poly clave key there is a series of characters and character states. Each state is followed by a number or code for the species that possess that feature.

> The user needs to select any character and then copy down the list of species that possess the feature. Then the user has to select another character and eliminate any species that is not common to both lists. This process has to be continued until the specimen is identified.

Construction of Keys:-

> Always use constant characters, not variables.

> Never use terms such as large/small, instead make correct measurements.

> Characters always available are to be used rather than seasonal characters.

> Always use positive terms. E.g. Stipule Is present - can be used but notstipule is not present.

> As far as possible both choices of a pair to be started with the same word. e.g. Seeds round, Seeds oblong.

> If possible different pairs of choices should start with different words. 

e.g. Flowers white, Sepals free 

                Flowers red, Sepals fused  

                        Corolla 1-2 mm long, Corolla 3-5 mm long

Proper Use of keys:-

> Appropriate keys to be selected from floras, manuals, handbook, monograph, revision etc.Cultivated plants- not usually given in floras. So for these- manuals treating such plants to be used.

> Introductory comments to be properly read first.

> Both leads should be read before making a choice. Sometimes the first lead may seem to be correct, the second lead may be more appropriate.

> The meaning of unknown terms should be checked using the glossary.

> When measurements are used such as the length of leaf, fruit etc. several materials/ specimens to be measured.

> No decision to be taken based on single observation.

> Results should be verified by reading a description, comparing the specimen with illustration or an authentic herbarium specimen.

Draw Backs of taxonomic keys:-

> The key may not include all potential variations in the sps.

> May rely on features not present in the season.

> May not include all sps of interest.

> One may misinterpret and make a mistake.