Numerical taxonomy may be defined as “method of grouping of taxonomical units by numerical methods”.
Hey wood defined numerical taxonomy as “numerical evaluation of the similarities between groups of organism and ordering of these groups into higher ranking taxa on the basis of these similarities.
In numerical taxonomy selected characters are studied using large populations. High speed computers are used for the purpose of comparision.
The main objective of the numerical taxonomy is to “classify and illuatrate the degree of relationship or similarities in an objective and repeated manner”.
Steps involved in numerical taxonomy :
1. Choice of operational unit (OTU): the first task in numerical taxonomy is to divide the basic unit called operational taxonomic unit or OUT which may be individuals, species, genera or even higher ranked taxon. It helps to study intraspecific and inter specific variations.
2. Characters (attribute) selection:
ü Large number of characters are to be selected from operational units.
ü 50-100 characters are rtaken into consideration.
ü The value of comparision becomes more stable with the increase in the number of characters taken into consideration.
· Charecters should be choosen from all the parts of the plants and all the stages in the life cycle.
· The taxonomic characters may be grouped into morphological, bio-chemical or ecological category.
· Collected data are processed.
3. By applying statistics to processed data percentage of similarities and percentage of dissimilarities are estimated.
4. After comparing the characters phenogram is constructed, indicating the relative resemblances and differnces between various taxa.