Following are the disadvantages of Five system of classification :-
• It puts unicellular algae in kingdom Protista but multicellular algae in kingdom plantae. However, both the organisms must belong to the same group.
• Thus organisms showing similarities are placed quite apart. For example unicellular and multicellular algae.
• Many organisms with dissimilarities have been put together in kingdom Protista. This leads to diversity in kingdom Protista.
• Viruses are entirely excluded from the five kingdom classification system.
• All organisms other than moneran shows that they are a polyphyletic in origin. It is a great shortcoming of five system of classification.