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Terminology of phylogenetic trees. This is a bifurcating tree. The vertical lines, called branches, represent a lineage, and nodes are where they diverge, representing a speciation event from a common ancestor. The trunk at the base of the tree, is actually called the root. The root node represents the most recent common ancestor of all of the taxa represented on the tree. Time is also represented, proceeding from the oldest at the bottom to the most recent at the top. What this particular tree tells us is that taxon A and taxon B are more closely related to each other than either taxon is to taxon C.
A phylogenetic tree is the only figure in On the Origin of Species, evidence of the central importance of such trees to evolutionary biology. As discussed in Chapter 5, a phylogenetic tree is a graphical representation of the evolutionary relationships among entities that share a common ancestor.o represent such events on a phylogenetic tree, the gene phylogeny is embedded within a tree that shows the species phylogeny (Fig. 27.28). The phylogeny of the gene can be represented separately, as shown in Figure 27.28B.