Galled Tree

A galled tree is one of the simplest types of phylogenetic networks. In a galled tree, cycles or loops are permitted among the branches, but they cannot build upon other cycles or loops. Formally, in a galled tree, any biconnected component contains at most one reticulate node—where a biconnected component is a subgraph of the tree for which two disjoint paths exist between node pairs in the component, and a reticulate node is a node with in-degree at least 2. This Ceiba tree has a “gall” around the hole in its trunk.

Photo: Noah Rosenberg, October 9, 2020