Final answer:
Phylogenetic trees illustrate the evolutionary order of events rather than time, showing how species are related through common ancestors, and they can be 'rooted' with a single common ancestor or 'unrooted' displaying relationships without a common starting point.
Step-by-step explanation:
The special aspect of the order on a phylogenetic tree is that the branches indicate the order of evolutionary events, not the length of time. Phylogenetic trees can be rooted or unrooted. Rooted trees have a single lineage representing a common ancestor from which all organisms on the tree are descended. Unrooted trees do not signify a common ancestor but still illustrate the relationships among species. Each branch on a phylogenetic tree represents a point where a single lineage evolved into distinct new ones. Critical to understanding these trees is that they show an evolutionary path does not end for the original branch when a new one begins. Also, the physical length of branches on the phylogenetic tree is typically not proportional to time unless explicitly indicated.