Plant Systematic is the biological classification of plants. It closely allied to plant taxonomy and it deals with the identification and ranking of all plants. It includes classification and nomenclature, and enables the botanist to comprehend the broad range of plant diversity and evolution. It involves relationships between plants and their evolution, especially at the higher levels. Later, classification and description was driven by natural history and natural theology. Until the advent of the theory of evolution, nearly all classification was based on the scale of nature. Relationships are visualized as evolutionary trees (cladograms, phylogenetic trees, phylogenies). Phylogenies have two components, branching order and branch length.