Linked from
The 22 pages that link to Incomplete lineage sorting, each with the reason it gives.
Species DelimitationRelated: It can make genetic markers disagree about where lineages split.
PhylogenomicsRelated: It produces discordant gene trees even when genes were inherited vertically.
SynapomorphyRelated: A gene variant shared by taxa may predate their common ancestor as a group.
CladeRelated: It can make the ancestry of closely spaced branches difficult to resolve.