Claim: Inferred evolutionary relationships are shown on a phylogenetic tree.

A phylogenetic tree or evolutionary tree is a branching diagram or `` tree '' showing the inferred evolutionary relationships among various biological species or other entities -- their phylogeny -- based upon similarities and differences in their physical or genetic characteristics . The taxa joined together in the tree are implied to have descended from a common ancestor . Phylogenetic trees are central to the field of phylogenetics .   In a phylogenetic tree , each node with descendants represents the inferred most recent common ancestor of the descendants , and the edge lengths in some trees may be interpreted as time estimates . Each node is called a taxonomic unit . Internal nodes are generally called hypothetical taxonomic units , as they can not be directly observed . Trees are useful in fields of biology such as bioinformatics , systematics , and phylogenetic comparative methods .   Unrooted trees illustrate only the relatedness of the leaf nodes and do not require the ancestral root to be known or inferred .