Final answer:
A 'rooted' phylogenetic tree diagram includes a single ancestral lineage, often at the bottom or left of the diagram, from which all organisms on the tree have diverged, representing a common ancestor.
Step-by-step explanation:
The term "rooted" on a phylogenetic tree diagram means that the tree has a common ancestor designated as the starting point from which all organisms represented in the diagram diverged. This common ancestor is typically drawn at the bottom or the left of the tree. Rooted trees, like the ones showing the three domains of life—Bacteria, Archaea, and Eukarya—indicate a single ancestral lineage from which various species evolved.
A "rooted phylogenetic tree" contrasts with an "unrooted" tree, which does not specify a common ancestor but still shows relationships among species. In rooted trees, the pattern of branching reflects the sequence of events that have led to the spread and diversification of a group of organisms over time. This helps to understand how recent and minuscule certain groups, such as plants and animals, are compared to other life forms in our evolutionary history.