A branching identification key within taxonomy (the practice and science of categorization or classification), is a presentation form of a single-access key where the structure of the decision tree is displayed graphically as a branching structure, involving lines between items.
[1] Depending on the number of branches at a single point, a branching key may be dichotomous or polytomous.
In a diagnostic key, the branching structure of the key should not be mistaken for a phylogenetic or cladistic branching pattern.
All single-access keys form a decision tree (or graph if reticulation exists), and thus all such keys have a branching structure.
"Branching key" may therefore occasionally be used as a synonym for single-access key.