Which characteristic were considered while placing fungi in a separate kingdom?

Explanation

R.H. Whittaker, an American taxonomist proposed five Kingdom classification in the year 1969.
The classification is based on the complexity of cell structure and organization of thallus.
It is based on the mode of nutrition
Separation of fungi from plants
Fungi are ubiquitous , eukaryotic, achlorophyllous heterotrophic organisms. They exist in unicellular or multicellular forms.