Plant Kingdom: The Plant Kingdom is defined as a multicellular, eukaryotic living organism where the cell wall contains chlorophyll, imparting green color to the plants. Broadly, the plant kingdom is divided into two classifications:

1. Cryptogame: The plants without seeds
2. Phanerogamae: The plants that bear seeds

Whittaker classified the whole living organism into five kingdoms based on the complexity of cell structure  (Prokaryotic and Eukaryotic), the complexity of the body (unicellular and multicellular), and mode of nutrition  (autotrophs and heterotrophs). 

Classification of the Plant Kingdom

All the classification systems, starting from that of Aristotle to the 20thcentury, can be divided into three types: 

1. Artificial System: In this system, the classification is based on few morphological characters.  Theophrastus, Pliny, and Linnaeus used an artificial system of classification.                              

2. Natural System: In this system, the classification is based on all the important related characters. Both external and internal. Bentham and hooker, Adanson, Candolle used a natural system of classification. 

3. Phylogenetic System: Classification based on the evolutionary relationship of plants. The use of phylogeny for classification was done by Eichler, Blessy, Whittaker, Engler, and Prantl, Hutchinson. 

Characteristics of Plant Kingdom