Taxonomy (from Ancient Greek:  taxis “arrangement”and Ancient Greek: nomia  “method”) is “the science of

identifying and naming species, and arranging them into a classification. ”-Wikipedia. This systematic classification of organisms was originally based on their visible similarity—as observed in herbaria specimens. The weakness of this approach is that organisms that look very similar may not be closely related. For example one non-poisonous species of snake may mimic another poisonous species. Cladistics, also known as phylogenetics, is a more modern way of analysing taxonomic relationships using objective quantitative analysis of data usually from DNA and RNA sequencing. The information gained from these studies can then be used to tweak the existing taxonomic classifications. Put simply a clade is a group that genetic analysis suggests has a single common ancestor