Five kingdom system of classification : R.H. Whittaker, an American ecologist. He proposed five kingdom system of classification in 1969.
This system replaced the old, two-kingdom grouping of living organisms. As already discussed, a division of living world merely into plant and animal kingdoms is too simple. It does not take into account the gradual evolution of distinct plant and animal groups and it allows no place for those primitive organisms that even now are neither plants nor animals nor that are both. In this classification eukaryotes were assingned to only four of the five kingdom.
Five-kingdom classification is based on the following four criteria :
(i) Complexity of cell structure.
(ii) Complexity of organism's body.
(iii) Mode of obtaining nutrition.
(iv) Phylogenetic relationship.
The five kingdom are : Monera, Protista, Fungi, Plantae and Animalia.