In biology, a reticulation of a single-access identification key

Single-access key

A 'key' in Biology is a modeling method used for categorizing species using logical choices. A single-access key is a key where the sequence and structure of identification steps is fixed by the author of the key...

 connects different branches of the identification tree to improve error tolerance and identification success . In a reticulated key multiple paths lead to the same result; the tree data structure thus changes from a simple tree to a directed acyclic graph

Directed acyclic graph

In mathematics and computer science, a directed acyclic graph , is a directed graph with no directed cycles. That is, it is formed by a collection of vertices and directed edges, each edge connecting one vertex to another, such that there is no way to start at some vertex v and follow a sequence of...

.

Two forms of reticulation can be distinguished: Terminal reticulation and inner reticulation.

• In a terminal reticulation a single taxon or next-level-key is keyed out in several locations in the key. This type of reticulation is normally compatible with any printable presentation format of identification keys and normally does not require special precautions in software used for branching keys.
• In an inner reticulation a couplet with further leads can be reached through more than one path. Depending on the software or printable presentation format, this be more challenging. For the linked (= "parallel" or "bracketed") format, where each lead points to a numbered couplet, inner reticulations present no special challenge. However, for the nested (= "indented") presentation format, where all following couplets immediately follow their lead, a cross-connection to a different subtree in the key requires a special mechanisms.

Reticulations generally improve the usability of a key, but may also diminish the overall probability of correct identification averaged over all taxa .