Level-1 Phylogenetic Network

The concept of a phylogenetic network extends the concept of a phylogenetic tree, permitting relationships among lineages to be described by a network structure rather than a tree structure. In a (rooted) level-1 phylogenetic network, terming a vertex formed by joining a pair of descendant lineages a reticulation node \(v\) and labeling the two immediate ancestors of \(v\) by \(u_1\) and \(u_2\), for each reticulation node \(v\), no reticulation nodes (other than \(v\)) exist in the pair of paths connecting \(v\) to the most recent shared ancestor of \(u_1\) and \(u_2\).