The arrangement of plants into groups and sub-groups on the basis of similarities is called classification. The characters which are uses as basis of classification are called criteria of classificat ion.
The classification system based on one or two morphological characters for the identification of plants is called artificial system.
The classification system which is based on set of characteristics for grouping similar plants is called natural system of classification. Various plants are grouped purely on the basis of morphological similarities in this system.
The classification system which grouped plants on the basis of set of morphological characteristics and phylogenetic relations is called phylogenetic system of classification.