Classification and evolutionary trees: what is the difference?

In a rooted tree, follow the branches of selected objects towards their shared node. The order of labels along the edge does not determine relatedness: branches can rotate around a node without changing the relationships. Read the connections. A clade contains a common ancestor and all its descendants in the corresponding branch.

Check the scale separately. A line may represent evolutionary change, elapsed time or simply a layout choice. Without supplied lengths and units, the distance between labels on the screen is not a measurement. Likewise, a number beside a node cannot automatically be read as its probability of being correct. Identify the support measure and method first.

A large synthesis tree can combine published phylogenies with a taxonomic framework. The Open Tree synthesis paper describes this approach. Inspect the basis of the particular relationship you need: a study, a classification placement or an unresolved connection. A large number of tips does not mean every branch has the same kind of evidence.

Try the route

Try it. Select two available groups, locate their shared node and open the evidence for the connection. Save the source version. Check whether a scale is supplied. If dates are absent, “dating is not provided” is a valid result; estimating an age from the drawing is not.

Read the example

Check your understanding. The teaching examples `(A,(B,C))` and `((C,B),A)` express the same relationships: B and C share the nearer common node relative to A. These letters are fictional labels, not a biological result. A tree of BRCA2 protein sequences is not automatically the complete history of the represented species. Its interpretation requires the sequence selection, method and relationship between gene and species events.

Teaching tree

The labels have moved; the branch connections are unchanged. A teaching topology.

In the teaching tree on this page, B and C meet at a node before their branch joins A. Within this shown topology, B and C are sister lineages. Moving a drawn tip left or right changes its position on screen, not that relationship. Since the example supplies no time scale, you cannot calculate when the lineages separated.