A phylogenetic network is anygraph used to visualize evolutionary relationships between species or organisms. It is employed when reticulate events such as hybridization, horizontal gene transfer, recombination, or gene duplication and loss are believed to be involved. Phylogenetic trees are a subset of phylogenetic networks. Phylogenetic networks can be inferred and visualised with software such as SplitsTree.
Many kinds and subclasses of phylogenetic networks have been defined based on the biological phenomenon they represent or which data they are built from (hybridization networks, usually built from rooted trees, recombination networks from binary sequences, median networks from a set of splits, optimal realizations and reticulograms from a distance matrix), or restrictions to get computationally tractable problems (galled trees, and their generalizations level-k phylogenetic networks, tree-child or tree-sibling phylogenetic networks).
Makarenkov, V., Kevorkov, D. and Legendre, P. (2006),Phylogenetic Network Reconstruction Approaches, Applied Mycology and Biotechnology, International Elsevier Series, vol. 6. Bioinformatics, 61-97.
A tutorial that reviews the terminology used for phylogenetic networks and covers both split networks and reticulate networks, their definition and interpretation.
