Tree-Child Network

Phylogenetic networks generalize the concept of a phylogenetic tree. The space of phylogenetic networks is large; it is sensible to define a variety of particular classes of network, so that analyses can be restricted to these classes.

A vertex \(v\) in a phylogenetic network is a reticulate vertex if it has in-degree 2 and out-degree 1. A vertex \(v\) is visible if there exists some leaf such that every path from the leaf to the root passes through \(v\). A network is tree-child if each of its vertices is visible. Each vertex is trivially visible in a phylogenetic tree; in the phylogenetic network produced by fusion of two branches of this coast live oak, the one reticulate vertex is visible, and the network is therefore a tree-child network.