A phylogenetic tree that illustrates relationships between the organisms or DNA sequences being studied, without providing information about the past evolutionary events that have occurred.

A cladogram for which the ancestor (= root) has not been hypothesized, and which thus does not specify the direction of evolutionary change among the character-states. An unrooted tree can be rooted on any of its branches, and so there are many rooted trees that can be derived from a single unrooted tree (cf. rooted tree).